VII.  The Final Rule


    A. Decision to Issue Two-Part Final Rule

    As noted above, NHTSA was required to submit a draft final rule to OMB for review. The agency submitted a draft final rule to OMB on December 18, 2001. During the review process, OMB raised questions about the available data and the conclusions the agency preliminarily drew from them. OMB also raised questions about the effect of the final rule on the installation of ABS and the possibility of obtaining braking safety benefits as well as tire safety benefits.

    To allow for the consideration of additional data regarding the requirements for vehicles manufactured after October 31, 2006, the agency has decided to divide the final rule into two parts. In this first part, the agency is establishing the requirements for vehicles manufactured from November 1, 2003 to October 31, 2006.

    The agency will leave the rulemaking docket open for the submission of new data and analyses. During this period, the agency requests that commenters address how the performance characteristics of particular types of TPMSs satisfy the statutory requirement that systems provide a warning "when a tire is significantly under-inflated."

    NHTSA is especially interested in data and information about TPMS, both the systems in the field as well as systems under development. Commenters are urged to provide substantiate their comments with data and information to the maximum extent possible. Unsubstantiated comments are less useful.

    The agency also will conduct a study comparing the tire pressures of vehicles without any TPMS to the pressures of vehicles with TPMSs, especially TPMSs that do not comply with the four-tire, 25 percent compliance option. Based on the record compiled to this date, the results of that study, and any other new information submitted to the agency, NHTSA will issue the second part of this rule. The second part will be issued by March 1, 2005, and will apply to vehicles that are manufactured after October 31, 2006.

    Based on the record now before the agency, NHTSA tentatively believes that the four-tire, 25 percent option would best meet the mandate in the TREAD Act. However, it is possible that the new information may be sufficient to justify a continuation of the requirements in the first part of this rule, or some other alternative.


    B. Part One of the Final Rule -- November 2003 through October 2006

    1. Summary

    The first part of this final rule establishes requirements for vehicles manufactured between November 1, 2003, and October 31, 2006, subject to a phase-in schedule. (52) The final rule requires passenger cars, multipurpose passenger vehicles, trucks, and buses with a GVWR of 4,536 kilograms (10,000 pounds) or less, except those vehicles with dual wheels on an axle, to be equipped with a TPMS to alert the driver that one or more of the vehicle's tires are significantly under-inflated.

    For these vehicles, the first part of the final rule provides two compliance options. (53) Under the first compliance option, a vehicle's TPMS must warn the driver when the pressure in one or more of the vehicle's tires, up to a total of four tires, is 25 percent or more below the vehicle manufacturer's recommended cold inflation pressure for the tires, or a minimum level of pressure specified in the standard, whichever pressure is higher. Under the second compliance option, a vehicle's TPMS must warn the driver when the pressure in any one of the vehicle's tires is 30 percent or more below the vehicle manufacturer's recommended cold inflation pressure for the tires, or a minimum level of pressure specified in the standard, whichever pressure is higher. (54)

    Vehicles certified to either compliance option will be required to provide written information in the owner's manual explaining the purpose of the low tire pressure warning telltale, the potential consequences of significantly under-inflated tires, the meaning of the telltale when it is illuminated, and what actions drivers should take when the telltale is illuminated. Vehicles certified to the one-tire, 30 percent option will be required to provide additional information on the inherent limitations of current indirect TPMSs.

    Under both compliance options, the TPMS must include a low tire pressure-warning telltale (yellow). Under the four-tire, 25 percent option, the telltale must remain illuminated as long as any of the vehicle's tires remains significantly under-inflated, and the key locking system is in the "On" ("Run") position. The telltale can be deactivated automatically only when all of the vehicle's tires cease to be significantly under-inflated, or manually in accordance with the vehicle manufacturer's instructions.

    The one-tire, 30 percent option requires that the telltale remain illuminated as long as one of the vehicle's tires remains significantly under-inflated, and the key locking system is in the "On" ("Run") position. The telltale can be deactivated automatically only when that tire ceases to be significantly under-inflated, or manually in accordance with the vehicle manufacturer's instructions. (55)

    Both compliance options require that the low tire pressure-warning telltale perform a bulb-check at vehicle start-up.

    Under both compliance options, each TPMS must be compatible with all replacement or optional tires (but not rims) of the size(s) recommended for use on the vehicle by the vehicle manufacturer. The TPMS is not required to monitor the spare tire, either when it is stowed or when it is installed on the vehicle. The TPMS also does not have to indicate a system malfunction.

    In response to comments regarding the need to manually reset indirect TPMSs after adding pressure to the tires, the agency is permitting the warning telltale to be deactivated manually, in accordance with the vehicle manufacturer's instructions.

    In response to comments regarding variations in rim designs, the agency is requiring TPMSs to be compatible with all replacement or optional tires, but not rims, of the size(s) recommended for use on the vehicle by the vehicle manufacturer.

    In response to BTS survey data indicating that 65 percent of people would be less concerned to either a great extent or a very great extent with routinely maintaining their tire pressure if their vehicle were equipped with a TPMS, the agency is requiring the low tire pressure warning telltale to perform a bulb-check during vehicle start-up.

    In response to comments, the agency is also making minor changes to the required written instructions, and requiring vehicles certified to the one-tire, 30 percent option to provide additional information on the inherent limitations of current indirect TPMSs.

    2. Congressional Intent

    Section 13 of the TREAD Act simply mandates "a rulemaking for a regulation to require a warning system in new motor vehicles to indicate to the operator when a tire is significantly under inflated." None of the sources of legislative history commonly recognized as being legally authoritative, such as the House and Senate Reports or the Congressional Record, shed any light on the type of TPMS that Congress intended to mandate with this amendment. (56)

    In the absence of any legally authoritative sources, the Alliance turned in its comments to statements made by Congressman Markey, the sponsor of the TPMS amendment, as quoted in an unofficial transcript of the House Committee on Energy and Commerce markup of the bill that became the TREAD Act. (57) In explaining and arguing for his amendment, Congressman Markey referred to a TPMS on an existing vehicle model. That TPMS was an indirect TPMS. Based on the Congressman's having mentioned an indirect TPMS in the course of his remarks, the Alliance argued that the Congressman must have intended that current indirect TPMSs be allowed under the rulemaking mandated by the TPMS amendment.

    While the Alliance's interpretation of Congressman Markey's statements during markup is not inconsistent with those statements, it goes well beyond anything that the Congressman directly said in them. Further, that interpretation is contrary to Congressman Markey's statements at the February 28, 2002 House Committee on Energy and Commerce hearing. In those later statements, Congressman Markey said that the intent of his TPMS amendment was to require TPMSs that provide warnings in all instances of under-inflation, thus suggesting a preference for direct TPMSs, which can provide such warnings, over current indirect TPMSs, which cannot. While those statements at the hearing likewise do not constitute any legally authoritative legislative history of the TREAD Act, they do suggest that the Alliance's interpretation of Congressman Markey's earlier statements is not persuasive.

    3. Vehicles Covered

    The final rule requires TPMSs on passenger cars, multipurpose passenger vehicles, trucks, and buses with a GVWR of 4,536 kilograms (10,000 pounds) or less, except those vehicles with dual wheels on an axle. It does not require TPMSs on motorcycles, trailers, low-speed vehicles, medium vehicles, or heavy vehicles.

    NHTSA is not requiring TPMSs on motorcycles because, unlike the types of vehicles that are subject to the final rule, some motorcycles still use tubed tires. In order for a direct TPMS to work with tubed tires, the pressure sensor would not only have to be inside the tire, but also inside the tube itself. The agency is not aware of any TPMSs that are made to work with tubed tires. The agency requested comments on this issue but received none.

    Advocates recommended that the agency open rulemaking to set regulatory requirements for retreaded and recapped medium (10,001 -- 26,000 pounds GVWR) and heavy (over 26,000 pounds) vehicle tires. Advocates stated that there is a "serious, pervasive problem of tire underinflation among medium and heavy vehicles, especially given the high percentage of trucks and buses above 10,000 pounds gross vehicle weight which use re-treaded tires." However, Advocates did not provide any data to support this statement.

    As discussed in the NPRM, NHTSA is not requiring TPMSs on medium (10,001 - 26,000 lbs. GVWR) and heavy (greater than 26,001 lbs. GVWR) vehicles at this time for two reasons. First, this rulemaking is required by the TREAD Act, which required a final rule to be issued in one year and was passed in response to problems with certain Firestone tires. Since those tires were used on light vehicles, and the time frame was so tight, the agency has limited its study of under-inflation to light vehicles.

    Second, the issues associated with under-inflated tires on medium and heavy vehicles are different from and more complex than the issues associated with under-inflated tires on light vehicles. For example, medium and heavy vehicles are equipped with tires that are much larger and have much higher pressure levels than the tires used on light vehicles. In addition, medium and heavy vehicles are generally equipped with more axles and tires than light vehicles. Since the TREAD Act imposed a one-year deadline on this rulemaking, the agency did not have the time to study and analyze those issues sufficiently.

    The Alliance recommended that the agency limit the applicability of the standard to vehicles having a GVWR of 3,856 kilograms (8,500 pounds or less). The Alliance stated that the majority of vehicles above 8,500 pounds GVWR are used commercially. The Alliance argued that such vehicles are maintained on a regular basis and do not need a TPMS to assist in maintaining proper inflation pressure in the vehicles' tires.

    NHTSA is aware of at least two non-commercial vehicle models -- the Chevrolet Suburban and Ford Excursion, both SUVs -- that have a GVWR between 8,500 and 10,000 pounds. In addition, 15-passenger vans are typically in this weight rating range. If the agency adopted the Alliance's recommendation, these vehicles would be excluded from the standard. These vehicles are as subject to under-inflated tires as other light SUVs and vans. Thus, the agency is not adopting the Alliance's suggestion.

    However, to address the Alliance's concern about the standard's applicability to commercial vehicles, the agency is excluding from the standard trucks, buses, and multipurpose passenger vehicles that have a GVWR under 10,000 pounds and dual wheels on an axle. This includes vehicles such as step vans, tow trucks, and some large pick-up trucks. The agency notes that these vehicles are normally used in a commercial capacity, and, as the Alliance argued, commercial vehicles normally undergo maintenance on a regular basis. Thus, these vehicles are less likely to experience significantly under-inflated tires. Moreover, since these vehicles have more wheels on an axle, they are less likely to experience the adverse effects on vehicle handling and other safety problems associated with significantly under-inflated tires.

    The Alliance also recommended that the agency explicitly exclude incomplete vehicles from the standard. (58) Normally, the first-stage vehicle manufacturer is responsible for certifying that all vehicle systems that are not directly modified by subsequent-stage manufacturers meet all Federal motor vehicle safety standards. The Alliance stated that, in the case of direct TPMSs, the first-stage manufacturer will be unable to guarantee that, even if physically undisturbed, a non-defective TPMS will function as required after vehicle modifications (such as adding metal hardware to the vehicle or lengthening its wheelbase) are made by subsequent-stage manufacturers.

    The agency notes that many incomplete vehicles are manufactured into custom vans and recreational vehicles. The agency believes that these vehicles should be equipped with the same or similar safety systems as passenger cars, multipurpose passenger vehicles, trucks, and buses. In particular, the agency believes that these types of vehicles should be equipped with a TPMS, as they are just as likely to experience significantly under-inflated tires as other light vehicles. In addition, the agency notes that if subsequent-stage manufacturers modify the TPMS on a vehicle, they will be responsible for certifying that the vehicle meets the standard. Therefore, the agency is not adopting the Alliance's suggested exclusion of incomplete vehicles.

    4. Phase-In Options and Requirements

    a. Alternatives Considered

    For purposes of this first part of the final rule, the agency considered four alternatives, three of which are discussed above in section V.A., "Alternative Long-Term Requirements Analyzed in Making Preliminary Determination." The fourth alternative considered by the agency is the one-tire, 30 percent alternative suggested by OMB. This alternative would require a vehicle's TPMS to warn the driver when the pressure in any one of the vehicle's tires is 30 percent or more below the placard pressure, or a minimum level of pressure specified in the standard, whichever pressure is higher. The benefits and costs of the one-tire, 30 percent alternative are discussed above in section VI.C. "Analysis of a Fourth Alternative Long-Term Requirement: One-Tire, 30 Percent Under-Inflation Detection."

    While the agency ultimately considered four alternatives, in the NPRM the agency proposed only two alternative versions of a standard for TPMSs and requested comments on them. The two alternatives were the four-tire, 20 percent alternative and the three-tire, 25 percent alternative.

    To simplify the agency's analysis and discussion of the comments, NHTSA is separately addressing below the two most significant aspects of these two alternatives, i.e., the definition of the term "significantly under-inflated" and the number of tires the TPMS should monitor.

    In the NPRM, the agency provided two alternate definitions of the term "significantly under-inflated," and then used that term in specifying performance requirements for the low tire pressure warning telltale, while not specifying any performance requirements for the TPMS itself. After reviewing this approach to drafting and organizing the regulatory text, the agency decided to adopt a simpler, more direct approach. Instead of defining the term "significantly under-inflated" in the final rule, the agency is specifying performance requirements, including the threshold level of under-inflation that must trigger a warning, for two compliance options: the four-tire, 25 percent option and the one-tire, 30 percent option.

    i. Threshold Level of Under-Inflation

    As explained above in section II.D, "Summary of Public Comments on Notice," RMA recommended that the agency define "significantly under-inflated" as any inflation pressure that is less than the pressure needed to carry the actual vehicle load on the tire per tire industry standards (or any pressure required to carry the maximum vehicle load on the tire if the actual load is unknown), or the minimum activation pressure specified in the standard, whichever is higher. RMA also recommended that the agency change the minimum activation pressures for P-metric standard load tires from 20 to 22 psi and for P-metric extra load tires from 23 to 22 psi. RMA also recommended that the agency change the "Maximum Pressure" heading in Table 1 to "Maximum or Rated Pressure" because light truck tires are not subject to maximum permissible inflation pressure labeling requirements. RMA recommended that the agency change the rated pressure for Load Range E tires from 87 to 80 psi. Finally, RMA, supported by RIGAC, recommended that the agency adopt a requirement in the agency's separate rulemaking to upgrade Standard No. 109, "New Pneumatic Tires," that "a tire for a particular vehicle must have sufficient inflation and load reserve, such that an inflation pressure 20 or 25 percent less than the vehicle manufacturer's recommended inflation pressure is sufficient for the vehicle maximum load on the tire, as defined by FMVSS-110." (59)

    The ITRA recommended that the agency consider only direct TPMSs. The ITRA stated that indirect TPMSs have too many limitations, including the inability to detect when all four of a vehicle's tires are significantly under-inflated. The ITRA claimed that although direct TPMSs are more expensive than indirect TPMSs, their benefits outweigh their costs.

    The Alliance recommended that the agency define "significantly under-inflated" as any inflation pressure 20 percent below a tire's load carrying limit, as determined by a tire industry standardizing body (such as the Tire and Rim Association) or the minimum activation pressure specified in the standard, whichever is higher. The Alliance agreed with the agency's minimum activation pressure of 20 psi for P-metric standard load tires.

    The Alliance also stated that a 25 percent differential from placard pressure would be inadequate to allow the use of indirect TPMSs. The Alliance claimed that a minimum of 30 percent differential is necessary to ensure accuracy with an indirect TPMS and avoid excessive nuisance warnings.

    The AIAM recommended that the agency define "significantly under-inflated" as any pressure more than 30 percent below the placard pressure. Alternatively, the AIAM suggested that the agency use the load carrying limit of the tire as defined by a tire industry standardizing body as the baseline for determining the warning threshold.

    TRW stated that indirect TPMSs that are currently on the market could be improved to detect a 25 percent differential in inflation pressure. TRW stated this could be accomplished by adding the equivalent of two direct pressure sensors and a receiver to an indirect TPMS.

    Advocates supported the definition of "significantly under-inflated" contained in the first alternative, i.e., any pressure 20 percent or more below the placard pressure, or the minimum activation pressure specified in the standard, whichever is higher.

    The agency notes that both RMA and the Alliance recommend that the agency tie the definition of "significantly under-inflated" to the load carrying capacity of the tire rather than the placard pressure. NHTSA declines to adopt this recommendation for two reasons.

    First, the placard pressure provided by the vehicle manufacturer assumes loading at GVWR and also takes into consideration ride, handling, and other factors for safe vehicle operation. Some manufacturers also include a certain amount of reserve load capacity in the event that the tire is overloaded. Therefore, when tire pressure is down to 25 percent below the placard pressure, it is not necessarily below the pressure that is needed to safely carry the weight of the vehicle. Moreover, the agency notes that the calculations in the Tire and Rim Association (T&RA) tables are based on the volume of air in the tire, and do not consider differing performance capabilities of different tire materials or manufacturing quality. (60)

    Second, consumers are currently not familiar with using the T&RA tables to determine the correct tire inflation pressure for their vehicles. However, they do have some familiarity with using the vehicle's placard pressure to maintain proper inflation pressures. It would be counter-productive to introduce a new frame of reference for consumers to use at this time unless there are compelling reasons to do so.

    The agency agrees with the Alliance's statement that most current indirect TPMSs are not able to detect a 25 percent differential from placard pressure. Of the indirect TPMSs evaluated by the VRTC, only one was capable of activating the warning telltale at pressures at least 25 percent below the placard pressure. (61)

    The agency believes that, as the technology matures, manufacturers will be able to improve the performance of indirect TPMSs. TRW, which manufactures both direct and indirect TPMSs, stated that the indirect TPMSs currently on the market could be improved to detect a 25 percent differential from placard pressure. However, TRW was not certain that these improvements could be developed and implemented by the 2003 effective date of the final rule. Sumitomo's comments indicated that indirect TPMSs would be able to detect a 25 percent differential in inflation pressure. Toyota stated that its next generation of indirect TPMSs would be able to detect a 20 percent differential in tire pressure by monitoring the resonance frequency as well as the dynamic radius changes of the tires. Again, however, Toyota did not have a timetable for the introduction of this next generation of indirect TPMSs.

    Nevertheless, the fact remains that current indirect TPMSs are not capable of meeting a four-tire, 25 percent requirement. Accordingly, the agency is providing two compliance options in the first part of the final rule. (62)

    These options will permit manufacturers to continue to use current indirect TPMSs while they continue to improve those systems. The agency notes that, for vehicles already equipped with ABS, the installation of a current indirect TPMS is the least expensive way of complying with the TPMS standard. Consumers will benefit from the resulting cost savings. The choice of compliance options will also give manufacturers the flexibility needed to innovate and improve the performance of the indirect TPMSs.

    NHTSA notes that in some cases, 30 percent below placard pressure will be less than 20 psi, the minimum activation pressure specified for P-metric tires in Table 1. For example, if a tire's placard pressure were 27 psi, 30 percent below that would be about 19 psi. This final rule requires the TPMS to activate the low tire pressure telltale at 20 psi, not 19 psi. The agency has established the minimum activation pressures for the reasons given below. This final rule requires the telltale to be activated at the higher of the pressure that is 30 (or 25) percent below the placard pressure or the minimum activation pressure in Table 1, whichever pressure is higher. Thus, if a vehicle's tires have a placard pressure below 28 psi, and the manufacturer chooses to comply with the one-tire, 30 percent option, the telltale must be activated at 20 psi.

    The agency is not adopting RMA's suggestion to change the minimum activation pressures for P-metric standard load tires from 20 to 22 psi and for P-metric extra load tires from 23 to 22 psi. As noted in the NPRM, the agency recently tested a variety of Standard Load P-metric tires at 20 psi with 100 percent load at 75 mph for 90 minutes on a dynamometer. None of the tires failed. This leads the agency to believe that warnings provided at or above that level will give drivers sufficient time to check and re-inflate their vehicles' tires before the tires fail. Moreover, in a different TREAD Act rulemaking, the agency proposed to upgrade its tire standard. (63) Part of this upgrade would require tires to be tested at 20 psi under load and speed conditions. All tires would be required to pass this test after completing the proposed endurance test. The agency believes these proposed tests would ensure that tires are capable of operating safely for at least 90 minutes at the minimum activation pressures specified in Table 1 of this final rule. Finally, RMA provided no reason for this change. The agency notes that until 2001, the T&RA tables listed 20 psi as the minimum acceptable pressure for Standard Load P-metric tires. The agency does not know why this minimum pressure was changed to 22 psi in the 2001 T&RA tables.

    The agency is adopting RMA's suggestion to change the "Maximum Pressure" heading in Table 1 to "Maximum or Rated Pressure" because light truck tires do not have maximum permissible inflation pressure labeling requirements. The agency is also adopting RMA's suggestion to change the rated pressure for Load Range E tires from 87 to 80 psi. The agency is also changing the corresponding kPa value from 600 to 550, and the corresponding minimum activation pressure from 350 to 320 kPa (51 to 46 psi).

    The minimum activation pressures are set forth in the following table: (64)


Table 1 - Low Tire Pressure Warning Telltale - Minimum Activation Pressure

Tire Type Maximum or Rated Inflation Pressure Minimum Activation Pressure
(kPa) (psi) (kPa) (psi)
P-metric -- Standard Load 240,
300, or
350
35,
44, or
51
140
140
140
20
20
20
P-metric - Extra Load 280 or
340
41 or
49
160
160
23
23
Load Range C 350 51 200 29
Load Range D 450 65 260 38
Load Range E 550 80 320 46


    Moreover, as noted above, part of the Standard No. 109 upgrade would require tires to be tested at 20 psi under load and speed conditions. All tires would be required to pass this test after completing the proposed endurance test. The agency believes these proposed tests, in effect, would require tires to have a reserve load.

    ii. Number of Tires Monitored

    As noted above, in the NPRM the agency proposed two alternatives: the four-tire, 20 percent alternative and the three-tire, 25 percent alternative. The agency specified only three tires in the three-tire, 25 percent alternative because currently available indirect TPMSs are not able to detect when all four of a vehicle's tires became significantly under-inflated.

    Advocates, ITRA, and RMA recommended that the agency require TPMSs to detect when all four of a vehicle's tires become significantly under-inflated. RMA argued that it is very likely that all four tires will lose air pressure at a similar rate and become significantly under-inflated within a six-month period. (65) RMA stated that drivers would rely heavily on TPMSs for tire pressure maintenance, which will make this scenario even more likely.

    The Alliance and AIAM recommended that the agency require TPMSs to detect significant under-inflation in only one of a vehicle's tires. The Alliance argued that TPMSs are not meant to replace the normal tire maintenance that would detect pressure losses due to natural leakage and permeation. Rather, TPMSs are designed to detect a relatively slow leak due to a serviceable condition, such as a nail through the tread or a leaky valve stem. Since such leaks rarely affect more than one tire simultaneously, the Alliance argued, it is sufficient to require TPMSs to detect only one significantly under-inflated tire.

    The Alliance also claimed that if the agency required that more than one significantly under-inflated tire be detected simultaneously, manufacturers would not be able to use an indirect TPMS. The Alliance stated that indirect TPMSs look at wheel speed to calculate relative differences in the size of the rolling radii of the four wheels. However, due to load variances, steering effects, and variations in tire characteristics, differences in wheel speed must be compared between tires on opposite sides of the vehicle for the algorithm to reliably identify a relative pressure difference.

    TRW stated that current indirect TPMSs could be improved to be able to detect more than one significantly under-inflated tire. TRW stated that this could be accomplished by adding a direct sensor to two wheels, one on each side of the vehicle.

    NHTSA agrees with the Alliance's comment that TPMSs should not replace normal tire maintenance. The agency also accepts the Alliance's comment that most current indirect TPMSs would have difficulty detecting when more than one of a vehicle's tires is significantly under-inflated. As noted above, while the VRTC found that indirect TPMSs did warn the driver when one tire, two tires located diagonally from each other, and three tires were significantly under-inflated, the indirect TPMSs did not warn the driver when all four of a vehicle's tires, or two tires on the same axle or the same side of the vehicle, were significantly under-inflated.

    However, the agency also believes that TPMSs should do more than detect a relatively slow leak due to a serviceable condition. There are other reasonably foreseeable circumstances in which significant under-inflation may occur. Further, the agency believes that many drivers will rely on the TPMS to prompt them to do inflation pressure maintenance. As noted above, data from the July 2001 BTS omnibus survey indicated that 65 percent of drivers would be less concerned with routinely maintaining their tire pressure if their vehicle were equipped with a TPMS.

    The agency has data indicating that tires typically lose about 1 psi per month due to natural leakage and permeation. Although all four of a vehicle's tires probably will not lose pressure at exactly the same rate, they will lose some pressure. Thus, it is likely that all four of a vehicle's tires will be somewhat under-inflated at any time.

    According to data from the February 2001 NCSA survey detailed above, 12 percent of passenger cars and 15.3 percent of light trucks with P-metric tires had at least two tires under-inflated by at least 25 percent; 5 percent of passenger cars and 7.2 percent of light trucks had at least three tires under-inflated by at least 25 percent; and 2.8 percent of passenger cars and 3.9 percent of light trucks had at least four tires under-inflated by at least 25 percent. If the agency adopted the Alliance's one-tire, 30 percent recommendation permanently, drivers of some vehicles, e.g., those equipped with current indirect TPMSs, would not be alerted to some of these potentially dangerous conditions. While these percentages are small, when applied to the entire light vehicle fleet (over 200,000,000 vehicles), these percentages translate into about 7,000,000 vehicles having all four tires significantly under-inflated at any time.

    If the agency adopted the Alliance's recommendation permanently, TPMSs would only be required to detect when one of a vehicle's tires became under-inflated by 30 percent or more below placard pressure. As a result, TPMSs would not be required to detect many situations involving significant under-inflation in the real world. Consequently, the agency tentatively believes that, in the long-term, the four-tire, 25 percent option would best meet the mandate in the TREAD Act and best serve the American public.

    However, as noted above in section VII.B.4.a.i., "Threshold Level of Under-Inflation," the agency wants to allow vehicle manufacturers to use current indirect TPMS in the short run, i.e., during the first part of this final rule, and to give them additional time to improve indirect TPMSs or develop hybrid TPMSs. The comments from TRW, Sumitomo, and Toyota indicate that current indirect TPMSs can be improved (whether by monitoring the resonance frequency of tires or by creating hybrid systems) to detect more than one significantly under-inflated tire.

    To reconcile the limitations of current indirect TPMSs with the agency's belief that such systems can and should be improved to enhance safety, NHTSA has decided to give manufacturers two compliance options during the first part of this final rule period, i.e., from November 1, 2003 through October 31, 2006. (66)

    b. Option One: Four Tires, 25 Percent Under-Inflation

    Under the first compliance option, a vehicle's TPMS must warn the driver when the pressure in one or more of the vehicle's tires, up to a total of four tires, is 25 percent or more below the vehicle manufacturer's recommended cold inflation pressure for the tires, or a minimum level of pressure specified in the standard, whichever pressure is higher. Vehicles certified to this compliance option also will have to comply with the remainder of the performance requirements, discussed below in section VII.B.5., "Other Requirements," with the exception of the special written instructions for vehicles certified to the one-tire, 30 percent compliance option.

    This compliance option is limited to light vehicles manufactured between November 1, 2003, and October 31, 2006. Light vehicles manufactured after October 31, 2006 will be subject to the requirements of the second part of this final rule, which the agency will publish by March 1, 2005. The remainder of the performance requirements, except for the special written instructions required for vehicles certified to the one-tire, 30 percent compliance option, will apply to light vehicles manufactured on or after November 1, 2003.

    c. Option Two: One Tire, 30 Percent Under-Inflation

    Under the second compliance option, a vehicle's TPMS must warn the driver when the pressure in any one of the vehicle's tires is 30 percent or more below the vehicle manufacturer's recommended cold inflation pressure for the tires, or a minimum level of pressure specified in the standard, whichever pressure is higher. (67) Vehicles certified to this compliance option also will have to comply with the remainder of the performance requirements, discussed below in section VII.B.5. "Other Requirements," including the special written instructions for vehicles certified to the one-tire, 30 percent compliance option.

    This compliance option also is limited to light vehicles manufactured between November 1, 2003, and October 31, 2006. Light vehicles manufactured after October 31, 2006 will be subject to the requirements of the second part of this final rule, which the agency will publish by March 1, 2005. The remainder of the performance requirements, except for the special written instructions requirement, will apply to light vehicles manufactured on or after November 1, 2003.

    d. Special Written Instructions for Option Two TPMSs

    In the NPRM, the agency proposed that the vehicle owner's manual provide an image of the TPMS warning telltale and the following information, in English:

    When the TPMS warning light is lit, one of your tires is significantly under-inflated. You should stop and check your tires as soon as possible, and inflate them to the proper pressure as indicated on the vehicle's tire inflation placard. Driving on an under-inflated tire causes the tire to overheat and can eventually lead to tire failure. Under-inflation also reduces fuel efficiency and tire tread life, and may affect the vehicle's handling and stopping ability.

    The agency also proposed to allow each vehicle manufacturer, at its discretion, to provide additional information about the significance of the low tire pressure warning telltale and description of corrective action that should be undertaken.

    The Alliance stated that it was not opposed to the language the agency proposed. However, the Alliance recommended that the agency include additional language addressing inherent system limitations, owner/driver responsibility, and replacement tires and rims. The Alliance did not recommend any specific language.

    NHTSA is accepting this Alliance comment. The agency notes that indirect TPMSs have several limitations, including the inability to detect when all four tires, and other combinations of tires, are significantly under-inflated. In addition, the agency notes that data from the July 2001 BTS omnibus survey indicate that 65 percent of drivers would be less concerned to a great extent or a very great extent with routinely maintaining their tire pressure if their vehicle were equipped with a TPMS. This substantial shift in reliance from routine maintenance to TPMS concerns the agency, given the performance limitations of indirect TPMSs. To avoid the creation of a false sense of security, therefore, the agency is requiring vehicle manufacturers to provide additional information on the inherent limitations of TPMSs, if the vehicle is certified to the one-tire, 30 percent option. The additional information must immediately follow the general written instructions for all TPMSs, specified below, and read, in English, as follows:

    Note: The TPMS on your vehicle will warn you when one of your tires is significantly under-inflated and when some combinations of your tires are significantly under-inflated. However, there are other combinations of significantly under-inflated tires for which your TPMS may not warn you. These other combinations are relatively common, accounting for approximately half the instances in which vehicles have significantly under-inflated tires. For example, your system may not warn you when both tires on the same side or on the same axle of your vehicle are significantly under-inflated. It is particularly important, therefore, for you to check the tire pressure in all of your tires regularly and maintain proper pressure.

    5. Other Requirements

    a. Time Frame for Telltale Illumination

    NHTSA notes that in the NPRM the agency included this performance requirement in the requirements for the low tire pressure warning telltale. After reviewing this arrangement, however, the agency has decided that it was confusing. Thus, in the regulatory text of this final rule, the agency has shifted this performance requirement to the section of the regulatory text that specifies requirements for TPMSs.

    In the NPRM, the agency proposed that the warning telltale illuminate not more than ten minutes after a tire becomes significantly under-inflated.

    Advocates supported a much briefer time period, but did not specify a time period. Advocates stated that the agency had given no reason for a ten-minute time period. RMA stated that the earlier the driver is warned the better, but also did not specify a time period.

    The Alliance stated that a detection window of ten minutes likely would be problematical for indirect TPMSs, which require different detection times at different speeds. The Alliance recommended that the detection requirement be changed to a driving interval of ten miles (16 kilometers) instead of ten minutes to accommodate indirect TPMSs.

    According to data from the tire industry, 85 percent of tire pressure losses are slow pressure losses, in which it takes anywhere from several minutes to several weeks for a tire to become significantly under-inflated. The other 15 percent of tire pressure losses are rapid pressure losses, which typically result from a tire being punctured (without the puncturing object becoming embedded in the tire) or ruptured. TPMSs are designed to alert the driver to slow pressure losses, not rapid pressure losses. In addition, as noted above, all of the tires that the agency tested for endurance at 20 psi for 90 minutes passed. Thus, the agency believes that ten minutes between the time that a tire becomes significantly under-inflated and the time that the TPMS illuminates the low tire pressure warning telltale will provide the driver ample time to take corrective action and avoid the possibility of serious tire degradation. Accordingly, the agency is not adopting Advocates' suggestion that the agency shorten the time frame for telltale activation.

    The agency notes that the test procedures proposed in the NPRM specified a test speed of 50 to 100 km/h. That means it would take a vehicle about 10 to 20 minutes to travel the 16 kilometers proposed by the Alliance. The agency also notes that in its survey of TPMSs, NHTSA's VRTC found that direct TPMSs could illuminate the warning telltale in less than one minute after a tire became significantly under-inflated (by 50 percent under placard pressure). The VRTC also found that indirect TPMSs took from less than a minute to over eight minutes. This leads the agency to believe that ten minutes is ample time for both direct and indirect TPMSs.

    Thus, the agency is not adopting the Alliance's suggestion that the agency change the detection requirement to a driving interval of ten miles instead of ten minutes.

    Accordingly, for the four-tire, 25 percent option, this final rule requires that the TPMS illuminate the low tire pressure warning telltale not more than ten minutes after the inflation pressure in one or more tires, up to total of four tires, is 25 percent or more below the placard pressure, or a minimum level of pressure specified in the standard, whichever pressure is higher. For the one-tire, 30 percent option, this final rule requires that the TPMS illuminate the low tire pressure warning telltale not more than ten minutes after the pressure in one tire is 30 percent or more below the placard pressure, or a minimum level of pressure specified in the standard, whichever pressure is higher. (68)

    b. Duration of Warning

    NHTSA notes that in the NPRM the agency included this performance requirement in the requirements for the low tire pressure warning telltale. After reviewing this arrangement, however, the agency has decided that it was confusing. Thus, in the regulatory text of this final rule, the agency has shifted this performance requirement to the requirements for TPMSs.

    In the NPRM, the agency proposed to require that the warning telltale be illuminated as long as any of the vehicle's tires remains significantly under-inflated, and the ignition switch is in the "On" ("Run") position, whether or not the engine is running. The agency also proposed that the telltale be deactivatable, manually or automatically, only when all of the vehicle's tires cease to be significantly under-inflated.

    Advocates and RMA supported this proposal. Advocates stated that if manual disengagement of the illuminated telltale were permitted, a driver could indefinitely defer inspecting and correcting a significantly under-inflated tire simply by manually disengaging the telltale.

    Johnson Controls, Inc. (JCI), a manufacturer of both direct and indirect TPMSs, was concerned that a strict reading of NHTSA's proposals may preclude a driver's ability to access other information when the significant under-inflation telltale is activated within a multi-functional console display. JCI argued that the agency should allow sufficient flexibility to permit the vehicle occupant to check other information on a multi-functional display even in a significant under-inflation situation. According to JCI, with current center displays in vehicles that incorporate a TPMS feature, the owner is allowed to toggle between features on the display. For example, on certain current tire and non-tire specific displays located in center consoles, the low pressure display will persist until the vehicle occupant chooses to view another display (e.g., a miles to empty display). In that circumstance, the new display will remain active for a period of 60 seconds and then the pressure warning will be redisplayed. In some instances, the redisplay will be accompanied by an audible warning. JCI argued that as long as alternative displays are selected by the vehicle occupant as a matter of conscious choice and are of sufficiently short duration, the cautionary function of the display will be preserved. Accordingly, JCI recommended amending Section 4.2.1(e) to read as follows:

    S4.2.1(e) Can be deactivated, manually or automatically, only when all of the vehicle's tires cease to be significantly under-inflated, or when the vehicle occupant chooses to view another feature on the same display provided that the pressure cautionary message is automatically redisplayed not more than 60 seconds after the display is toggled to another feature.

    The Alliance stated that the requirement that the warning telltale be deactivated, manually or automatically, only when all of the vehicle's tires cease to be significantly under-inflated requires the vehicle to "know" that all the tires have ceased to be significantly under-inflated. This would prohibit the use of indirect TPMSs, which do not measure actual inflation pressure, and are therefore incapable of "knowing" when the tires are no longer significantly under-inflated. This is the reason indirect TPMSs come with a manual re-calibration capability -- because all indirect TPMSs must be "told" that repair, rotation, replacement, or re-inflation has occurred.

    The Alliance also noted that some vehicles have different placard pressures for the front and rear tires. For these vehicles, the TPMS warning cannot be fully automated. The driver or service agent must manually recalibrate the TPMS after rotating or correctly inflating the tires. For these reasons, the Alliance recommended amending Section 4.2.1(d) to read as follows:

    S4.2.1(d) Remains activated (continuously or periodically) until automatically deactivated when all of the vehicle's tires cease to be significantly under-inflated or until manually deactivated in accordance with manufacturer's instructions.

    NHTSA is not adopting JCI's suggestion because the agency does not believe the driver should be able to temporarily deactivate the warning telltale, even if the deactivation can only last for 60 seconds. The agency does not normally allow warning telltales to be temporarily deactivated by the driver. The agency also believes that the warning telltale should be separate from a reconfigurable display.

    However, NHTSA is adopting the Alliance's suggestion that the agency allow the warning telltale to be manually extinguished in accordance with the vehicle manufacturer's instructions. The agency agrees with the Alliance's arguments. An indirect TPMS cannot "know" when a tire is no longer significantly under-inflated because it does not actually measure inflation pressure. An indirect TPMS must be told that the significantly under-inflated tire has been re-inflated. This is done with a manual reset button.

    The agency noted in the NPRM that a reset button may invite human error. For example, a driver may accidentally press the reset button when one or more of the vehicle's tires are under-inflated, but not significantly under-inflated. This would re-calibrate the system so that the under-inflated condition would be accepted as a normal variable. The indirect TPMS then would not be able to detect a significantly under-inflated tire until one or more tires were 25 percent lower than it already was. This could also occur as a result of misuse, i.e., if the driver simply pressed the reset button when the warning telltale illuminated. The telltale would be extinguished without the driver having taken any corrective action.

    While NHTSA is concerned by these potential problems, the agency notes that indirect TPMSs must have a reset button. Moreover, direct TPMSs need a reset button under certain circumstances. For example, some vehicle manufacturers specify more than one placard pressure for a vehicle's tires -- one applicable when the vehicle is lightly loaded and another when the vehicle is at maximum load. If a manual reset were not allowed, then the direct system would not know that the applicable recommended inflation pressure had changed.

    In addition, these human error problems are no different from the driver simply ignoring the warning telltale if it is illuminated. The agency can attempt to prevent these problems only through driver education. Thus, the agency will allow the warning telltale to be deactivated manually in accordance with the vehicle manufacturer's instructions.

    Accordingly, the agency is adding paragraph S4.2.1(b) to the requirements for the four-tire, 25 percent option, to read as follows:

    (b) Continue to illuminate the low tire pressure warning telltale as long as the pressure in any of the vehicle's tires is equal to or less than the pressure specified in (a), and the key locking system is in the "On" ("Run") position, whether or not the engine is running, or until manually reset in accordance with the vehicle manufacturer's instructions.

    The requirement for the one-tire, 30 percent option is slightly different because under that option the TPMS only has to be able to detect when one tire is 30 percent or more below the placard pressure. Accordingly, the agency is adding paragraph S4.2.2(b) to the requirements for the one-tire, 30 percent option, to read as follows:

    (b) Continue to illuminate the low tire pressure warning telltale as long as the pressure in that tire is equal to or less than the pressure specified in (a), and the key locking system is in the "On" ("Run") position, whether or not the engine is running, or until manually reset in accordance with the vehicle manufacturer's instructions.

    c. Temporary Disablement

    The Alliance noted that TPMSs might be disabled, deliberately or by default, under certain conditions. For example, TPMSs could be disabled on four-wheel-drive applications whenever the vehicle is operated in "4WD Lo" mode, typically during off-road use, or under very poor road conditions. The Alliance noted that most manufacturers of four-wheel-drive vehicles recommend that the tires be deflated to a lower pressure during certain conditions of off-road use. A TPMS calibrated to a threshold appropriate for on-road use would otherwise provide an unnecessary warning under this special condition. The Alliance also stated that certain types of all-wheel-drive vehicles that selectively lock the differential under specific operating conditions typically disable the TPMS under these conditions. The Alliance concluded that such selective disablement is inconsequential to safety, as vehicles operating under such conditions are generally moving at relatively slow speeds where low tire pressure is not a significant safety concern.

    The Alliance also stated that TPMSs may be temporarily disabled or reduced in detection sensitivity by default due to technical limits on system capability. For example, indirect TPMSs are not capable of operating normally on rough roads, or at very high speeds (i.e., above 75 mph) where the high centrifugal force prevents accurate detection of differences in rolling radius. Direct TPMSs are not capable of operating when radio frequency interference disrupts the transmission of sensor signals between the wheel sensors and the receiver, or when a tire without a sensor (such as a temporary spare) is installed on the vehicle.

    NHTSA has decided to prohibit any control that automatically disables the TPMS under any condition. The agency normally does not allow safety systems to be disabled, and the Alliance has provided no good reason for allowing the TPMS to be disabled. If drivers lower their tire pressure before off-road driving, and the low tire pressure warning telltale illuminates, it will serve as a reminder to the drivers to re-inflate their tires before returning to the road. The agency does not believe that drivers will be inconvenienced if the telltale illuminates while they are driving off-road. Moreover, the Alliance indicated that drivers may also shift into "4WD-Lo" while driving on very poor road conditions. Since tire under-inflation plays a role in vehicle handling and stability, the agency believes that it is especially important that the TPMS be functioning when the vehicle is being driven on poor road conditions.

    Finally, the agency notes that all technology has limitations, and there may be situations in which the TPMS may not function properly. The agency considered those situations in specifying the test conditions and procedures in this standard. The agency will not perform compliance tests under any conditions or procedures that would prevent TPMSs from functioning properly.

    d. System Calibration

    In the NPRM, the agency noted that most indirect TPMSs need time to calibrate the system, i.e., to "learn" the variables associated with distinct tire types under varying driving conditions. In its survey of current TPMSs, the VRTC found that the four indirect TPMSs it evaluated took anywhere from several minutes to several hours to calibrate. This calibration is necessary when a vehicle is driven for the first time (i.e., when it is new), when the pressure in a tire is changed, and when the tires are rotated or replaced. During the calibration mode, an indirect TPMS's ability to monitor tire pressure is severely limited. Thus, if one or more tires became significantly under-inflated while the system was calibrating, the driver might not be alerted.

    The agency did not propose in the NPRM that the TPMS indicate to the driver that the system is in calibration mode. However, in the proposed test procedures, the agency specified that the vehicle be driven for 20 minutes to allow for system calibration. Thus, in effect, the agency required that TPMSs be able to calibrate within 20 minutes of driving.

    The Alliance recommended that the agency allow manufacturers to provide, but not require, a calibration notification feature. The Alliance stated that recalibration generally takes place after the driver inflates the tires to the correct pressure. The driver then would be aware that calibration was taking place. The Alliance also argued that the likelihood of another significantly under-inflated tire occurring during the recalibration time frame is extremely low.

    TRW recommended that the agency not require indirect TPMSs to indicate that they are in calibration mode. TRW stated that this feature would not be necessary with direct TPMSs because they do not require calibration.

    The agency has decided not to require that the TPMS indicate when it is in calibration mode. The agency notes that calibration is necessary only for indirect TPMSs, and then it is necessary only when a vehicle is driven for the first time, when the pressure in a tire is changed, and when the tires are rotated or replaced. These are all times when significant under-inflation due to a slow leak should not be a problem. At these times, the tires either will be new or will have been checked. In addition, the agency notes that the driver is not able to take any action when given an indication of system calibration. For these reasons, the agency does not believe that a calibration indication feature would provide any safety benefits. However, if manufacturers wish to provide a calibration notification feature, they are free to do so. The agency is not prohibiting such a feature.

    e. Replacement Tires

    In the NPRM, the agency proposed to require that each TPMS be able to function properly when any of the vehicle's original tires or rims are replaced with any optional or replacement tire or rim of the size(s) recommended for use on the vehicle by the vehicle manufacturer.

    RMA supported the agency's proposal. Advocates recommended that the agency require TPMSs to function properly with all replacement tires and rims, regardless of size.

    The Alliance recommended that the agency require TPMSs to function properly only with those tires and rims offered as original or optional equipment by the vehicle manufacturer. The Alliance stated that there are a large number of replacement brands and types of tires and rims with different dynamic rolling radii, size variations, load variations, and temperature characteristics. The Alliance argued that since vehicle manufacturers do not control tire compliance for aftermarket tires and rims, they cannot guarantee that the TPMS will work, or will work with the same level of precision, in all cases.

    JCI requested that the agency clarify that it was not requiring TPMSs to function when custom tires and rims not recommended by the vehicle manufacturer are installed on the vehicle. JCI stated that both indirect TPMSs (because of tire diameter changes and different tire pressure thresholds) and direct TPMSs (because of the potential inability to install and operate the transmitter) are compromised by such installations.

    The Specialty Equipment Market Association (SEMA) claimed that the proposed rule would have a major effect on business that sell aftermarket tires and rims. SEMA was concerned that the rule could: (1) disallow aftermarket equipment that does not match the vehicle manufacturer's recommendations; (2) fail to require manufacturers to implement the TPMS in a manner that allows reprogramming by aftermarket installers; (3) fail to require that vehicle manufacturers design tire pressure sensors to be compatible with aftermarket tire and wheel combinations and standardized communication protocols to ensure that aftermarket sensors are compatible with OEM systems; (4) fail to direct consumers to inflate the tire to the pressure for the specific wheel and tire combination in use; and (5) render servicing by independent repair facilities more difficult.

    In this final rule, the agency is requiring that each TPMS meet the requirements of the standard when any of the vehicle's original tires are replaced with any optional or replacement tire of the size(s) recommended for use on the vehicle by the vehicle manufacturer and installed on the original rims. This requirement is the same for TPMSs complying with the four-tire, 25 percent option or the one-tire, 30 percent option.

    The agency is not requiring that TPMSs meet the requirements of the standard when any of the vehicle's original rims are replaced with any optional or replacement rim of the size recommended for use on the vehicle by the vehicle manufacturer. The agency notes that since most direct TPMS sensors are mounted on the rim, the rim must be of a design that will accommodate the sensor. Some aftermarket rims may be the same size as the original rim, but have a design that will not accommodate a TPMS sensor. Thus, the agency does not believe that requiring TPMSs to work with all replacement rims of the same size recommended for use by the vehicle manufacturer is feasible.

    However, the agency does believe that requiring TPMSs to work with all replacement tires of the same size recommended by the vehicle manufacturer is feasible. The agency notes that while tires may have different designs, they are basically designed to meet tire industry standards. The agency also notes that aftermarket direct TPMSs currently are available on the market. These TPMSs necessarily must be able to function regardless of the brand of tire. Moreover, RMA supported the agency's proposal to require TPMSs to work with all replacement tires of the same size or size recommended by the vehicle manufacturer. RMA did not state that this would be impossible due to differences in tire brands.

    The agency emphasizes that this requirement only applies to replacement tires that are of a size recommended for use on the vehicle by the vehicle manufacturer. It does not apply to any tires of a size not recommended for use on the vehicle by the vehicle manufacturer. If a tire retailer or repair business installs these tires on a vehicle, neither this final rule nor the statute under which it is issued requires the vehicle's TPMS to continue to meet the requirements of the final rule.

    NHTSA notes that 49 U.S.C. 30122 prohibits manufacturers, distributors, dealers, and motor vehicle repair businesses from knowingly making inoperative any part of a device or element of design installed on or in a motor vehicle or motor vehicle equipment in compliance with an applicable Federal motor vehicle safety standard. The agency has determined that if such a business installed on a vehicle aftermarket rims that are not identical to the original rims, or tires that are not of the same size recommended for use on the vehicle by the vehicle manufacturer, the business would not violate the make inoperative provision. However, if such a business knowingly renders a vehicle's TPMS inoperative while rotating the vehicle's tires or installing tires that are of the same size recommended for use on the vehicle by the vehicle manufacturer, and does not repair the TPMS, the business has violated the make inoperative provision.

    f. Monitoring of Spare Tire

    In the NPRM, the agency did not propose that the TPMS be required to monitor the pressure in the spare tire because NHTSA does not require vehicles to be equipped with a spare tire.

    Advocates and RMA recommended that the agency require TPMSs to monitor a vehicle's spare tire. RMA argued that the spare tire should be monitored to ensure its functionality, if and when it is needed. Advocates stated, "Vehicle owners chronically neglect to maintain minimal air pressure in spare tires." However, Advocates did not provide any evidence to support its position.

    The Alliance recommended that the agency require TPMSs to monitor only matching, full-size spare tires, and only when they are installed on the vehicle (i.e., not while they are stowed). The Alliance stated that temporary-use spare tires, including full-size, non-matching and compact spare tires, are not intended to be part of the normal tire rotation cycle for the vehicle. Because these temporary-use spare tires degrade the esthetic appearance or have speed and distance limitations, vehicle owners normally replace them quickly. Thus, the Alliance recommended that the agency not require TPMSs to monitor temporary-use tires, whether stowed or installed on the vehicle. However, the Alliance recommended that the agency require the TPMS to monitor a matching, full-size spare tire when it is installed on the vehicle.

    The agency has decided not to require TPMS to monitor the spare tire, either when the tire is stowed or when it is installed on the vehicle, for several reasons.

    First, temporary-use tires are not intended to be used on the road for long periods of time. The agency also notes that compact spare tires pose problems for both direct and indirect TPMSs. A compact spare requires much a higher inflation pressure and a different warning threshold. A compact spare is also much smaller, and thus has a smaller rolling radius, than original tires. This could cause an indirect TPMS to give a false warning.

    Second, drivers know when a temporary-use spare tire has been installed on the vehicle, and they know that the tire is intended for temporary-use only. The agency believes that most, if not all, drivers will have such spare tires replaced as quickly as possible. For these reasons, the agency is not requiring the TPMS to monitor temporary-use spare tires, including compact spares and non-matching, full-size temporary tires.

    Notwithstanding the Alliance's comment, the agency does not believe that matching, full-size spare tires need be monitored, even though such tires may be used in the tire rotation. The agency has no data indicating how many vehicles are provided with a matching, full-size spare tire. In addition, the agency is concerned that requiring the TPMS to monitor the spare tire would add to the cost of the rule significantly because vehicle manufacturers would have to provide an additional pressure sensor (in the case of a direct TPMS) and a matching rim, with little, if any, safety benefit. Finally, the agency is concerned that requiring this would provide a disincentive to vehicle manufacturers to provide vehicles with matching, full-size spare tires.

    g. Temperature Compensation

    In the NPRM, the agency noted that when a vehicle is being driven, the temperature in its tires increases. The increased temperature causes increases in the inflation pressure of the tires. (69) This phenomenon could impact the ability of a TPMS to measure or calculate the cold inflation pressure in a tire accurately. A temperature compensation feature in a TPMS compensates for the increased inflation due to temperature increases.

    It is possible that, without temperature compensation, the low tire pressure warning telltale could be extinguished due to the increase in tire pressure experienced during normal driving. For instance, if a vehicle's tires became significantly under-inflated overnight, while the vehicle's tires were cold, the low tire pressure warning telltale would be illuminated. However, if the driver did not re-inflate the vehicle's tires, the temperature of the tires, and thus the inflation pressure, would increase during normal driving. This could cause the telltale to be extinguished.

    In addition, large fluctuations in the ambient temperature could result in the low tire pressure warning telltale's being activated on vehicles during ignition, and then automatically de-activated, if the vehicle has that capability, after the vehicle has been driven for a while and the temperature (and thus the pressure) in a tire increases.

    NHTSA did not propose that TPMSs have a temperature compensation feature. The agency believed that such a feature would add to the cost of the proposed standard and that indirect TPMSs would not be able to meet such a requirement. NHTSA did, however, request comments on whether such a feature should be required.

    The Alliance commented that indirect TPMSs do not require temperature compensation because temperature variances are accounted for naturally in the rolling radii of the tires. Moreover, increases in temperature, and thus in pressure, affect all of a vehicle's tires equally. Thus, the pressure in all four tires increases similarly and does not affect an indirect TPMS's calculation of tire pressure.

    The Alliance also stated that direct TPMSs may employ temperature compensation to prevent nuisance warnings. The Alliance recommended that the agency not require temperature compensation because good engineering practices and concern for customer satisfaction (i.e., by preventing nuisance warnings) will compel this feature where needed, regardless of regulation.

    Advocates and the EC recommended that the agency require temperature compensation. Advocates stated that temperature compensation is crucial not only to reliable operation of TPMSs in providing accurate detection and notification of low pressure conditions in tires, but also to ensure that TPMSs provide positive feedback and confidence among vehicle operators as meaningful indicators of incipient safety problems which require rapid attention. Advocates expressed concerned that without temperature compensation, the low tire pressure warning telltale would activate and de-activate with temperature, and corresponding pressure, increases. Advocates believed this would encourage drivers to ignore the warning telltale. The EC suggested that temperature compensation might be necessary to ensure the reliability and accuracy of TPMSs.

    NHTSA has decided not to address this in this new standard. As noted in the Alliance comments, indirect TPMSs do not need temperature compensation. For direct TPMSs, the agency believes that it is appropriate to allow flexibility to address issues like these, particularly in the early stages of a technology like TPMS. If real-world experience shows that the public is getting nuisance warnings, the agency will revisit this issue.

    h. Low Tire Pressure Warning Telltale

    The performance requirements for the low tire pressure warning telltale discussed below are the same for both the four-tire, 25 percent option and the one-tire, 30 percent option.

    i. Color

    In the NPRM, the agency proposed to require that the color of the warning telltale be yellow. The agency received several comments on this issue.

    Advocates recommended that the agency require the color to be red. Advocates stated that a number of current lighted warning telltales providing status information to driver of vehicle operating systems (e.g., brake systems and engine oil) use red lamps. Advocates argued that, in most cases, an imminent safety hazard is not present when these warning lamps are illuminated, yet their color is red. Advocates also argued that the low tire pressure warning telltale would alert drivers about the existence of a potentially dangerous situation that needs rapid correction. Advocates stated that a red lamp would convey this urgency to drivers better than a yellow lamp.

    The Alliance agreed that yellow is the appropriate color for the warning telltale. However, the Alliance recommended that if a manufacturer chooses to imbed the warning telltale in a reconfigurable display, the telltale be excluded from the yellow color requirement. The Alliance argued that the changing appearance of the display would serve the purpose of drawing the driver's attention to the warning, which is otherwise accomplished by lighting a lamp.

    The agency is not adopting Advocates' suggestion. The use of the color red for telltales is usually reserved for telltales warning of an imminent safety hazard. The brake systems warning telltale is required to be red because a failure in a vehicle's brake system results in an imminent safety hazard that requires immediate attention. The agency does not believe that a significantly under-inflated tire represents an imminent safety hazard. As noted above, the agency has tested a variety of tires at 20 psi, the minimum activation pressure for the warning telltale, for 90 minutes. None of the tires failed. In addition, as noted above, the agency will propose to test all Standard Load P-metric tires at 20 psi under load and speed conditions for 90 minutes after they undergo a stringent endurance test. This proposal was included in the agency's NPRM to upgrade its tire standard. (70) The agency believes that these tests will ensure that tires will be able to operate safely for at least 90 minutes at the minimum activation pressures specified in this standard. Moreover, the agency notes that since most Standard Load P-metric tires have a placard pressure of at least 30 psi, the warning telltale will have to illuminate at a pressure above the minimum activation pressure. Accordingly, the agency concludes that yellow is the appropriate color because it conveys the message that the driver can continue driving, but should check and adjust the tire pressure at the earliest opportunity.

    NHTSA is also not adopting the Alliance's suggestion. The agency notes that reconfigurable displays can be reconfigured by the driver. The driver might reconfigure the display to not show the tire pressure for hours, days, or weeks at a time. Thus, if the low tire pressure warning telltale were imbedded in the reconfigurable display, the driver might not be alerted to the existence of a significantly under-inflated tire. The agency has no objection if manufacturers wish to use a reconfigurable display to display individual tire pressure. However, the agency does not believe the telltale itself should be imbedded in a reconfigurable display. (71) Thus, the agency is not adopting the Alliance's suggestion that the agency exclude reconfigurable displays from the color requirement.

    ii. Symbol

    In the NPRM, the agency proposed three symbols for the low tire pressure warning telltale. The first was an image of the vehicle with lamps located at the image's tires to indicate which tire is significantly under-inflated. The agency noted that such an image, with lamps around the image that illuminate when there is a problem (e.g., an incompletely closed door) in that area, is already built into the dashboard of some vehicles. Thus, the agency proposed that this image, with lamps at the image's tires to indicate which tire is significantly under-inflated, be required if a vehicle manufacturer provides a display that identifies which tire is significantly under-inflated.

    The agency received no comments opposing the use of this image. Thus, the final rule requires the use of this image, with lamps at the image's tires to indicate which tire is significantly under-inflated, if a vehicle manufacturer provides a display that identifies which tire is significantly under-inflated.

    In addition to the vehicle image, the agency proposed a choice between two symbols for TPMSs that do not inform the driver which tire is significantly under-inflated. The first was developed by the International Organization for Standardization (ISO). It is used to identify tire malfunctioning and is currently used in some vehicles with TPMSs. The second was a symbol of a low tire developed by the agency. All three symbols are set out below:



ISO Symbol

ISO Symbol



NHTSA Low Tire Symbol

NHTSA Low Tire Symbol



Vehicle Symbol Indicating Which Tire Is Significantly Under-Inflated

Vehicle Symbol Indicating Which Tire Is Significantly Under-Inflated



    Prior to issuing the NPRM, the agency conducted symbol comprehension tests to aid the agency in determining which symbol best conveyed a tire pressure problem to drivers. The agency asked 120 people to look at 15 symbols, including the ISO symbol and the low tire symbol developed by the agency, and fill in the blank in the following statement: "This image has just appeared on your vehicle's dashboard. It is a warning for _____."

    Results of this test indicated that the ISO symbol was the least understood among the 15 symbols, with a comprehension rate of only 38 percent. The low tire symbol developed by the agency had a comprehension rate of 100 percent.

    The agency received several comments on this issue. Advocates and ITRA recommended that NHTSA require the low tire symbol developed by the agency because it had high recognition value, while the ISO symbol had low recognition value.

    The Alliance recommended that the agency require the ISO symbol for several reasons. First, the Alliance argued that while the agency-developed low tire symbol is easier to recognize than the ISO symbol on paper, it is not easier to recognize when reduced to the size, and placed in the medium, that would be used for a dashboard display. (72) The Alliance claimed that on a dashboard display, the resolution of the low tire symbol would not allow for the flat portion of the tire to be seen. The ISO symbol, according to the Alliance, remains visible and recognizable, even when reduced and placed in a dashboard.

    Second, the Alliance argued that the low tire symbol falsely indicates that a tire is flat, rather than that pressure is low. The ISO symbol does not provide this misleading information.

    Third, the Alliance argued that while the ISO symbol initially may not be recognized as a low tire warning, the near-universal requirement for TPMSs will rapidly lead to widespread recognition of whatever symbol NHTSA ultimately decides to require.

    Finally, the Alliance argued that the ISO symbol has already been adopted as a voluntary standard and is in widespread use among those manufacturers currently offering TPMSs. Were NHTSA to require a unique symbol for the U.S. market, manufacturers who already use the ISO symbol would be required to re-tool their instrument clusters to accommodate the unique symbol. According to the Alliance, this would be expensive and time-consuming.

    ITRA recommended that the agency require an audible warning as well as a warning lamp. ITRA stated that many drivers ignore a warning lamp, especially on bright days.

    The agency agrees with the Alliance's arguments. Although the NHTSA-developed low tire symbol had a high recognition rate on paper, its level of detail, and thus its recognition rate, might not be retained when reduced in size and translated from paper to a dashboard display. Moreover, the agency believes that when TPMSs are first introduced, no matter what symbol the agency requires, drivers will consult their owner's manual to determine exactly what the symbol means and what they should do when the telltale illuminates. Drivers then will associate that telltale with a significantly under-inflated tire. Finally, the agency is interested in harmonizing its standards when it can do so consistent with the interests of safety. Since the ISO symbol is currently being used by manufacturers in Europe and the U.S., and since it will likely be readily learned, the agency can easily harmonize this requirement. For these reasons, the agency is requiring the ISO symbol. The agency also has decided to allow the use of the words "Low Tire" with the ISO symbol so that drivers will become familiar with the low tire pressure warning telltale more rapidly.

    The agency is not requiring an audible warning in addition to the telltale lamp. The agency notes that although ITRA stated that many drivers ignore a warning lamp, it provided no such evidence. The agency believes that requiring an audible warning would increase the cost of TPMSs without providing any additional benefits.

    iii. Self-Check

    In the NPRM, the agency did not propose that the TPMS conduct a self-check or a bulb-check at vehicle start-up. However, it did request comments on the desirability of requiring such a check.

    Advocates strongly supported both a system-check and a bulb-check. Advocates stated that vehicle systems regularly provide a system readiness check or a bulb-check to provide an initial indication to the driver that the system is operational. Advocates recommended a system- and bulb-check which provides several seconds of separate notification to the driver after the vehicle is started instead of the fleeting notification which is usually supplied only when the ignition is first engaged.

    RMA also supported both a system-check and a bulb-check. RMA argued that, with the broad installation of TPMSs, much of the motoring public will rely heavily on the systems for tire inflation maintenance. The frequency of routinely checking tire pressure is expected to drop significantly. Accordingly, RMA recommended that TPMSs go through a self-diagnostic check, including a bulb-check, with each vehicle start-up to indicate to the driver that the system is operational.

    TRW stated that both direct and indirect TPMSs could perform a bulb-check and a self-check. TRW stated that with direct TPMSs, each tire pressure sensor can be set to periodically transmit an indication that it is functioning. If a sensor is not transmitting, or a sensor's battery is low, the receiver can send a system-malfunction message to the vehicle's body control module and illuminate the TPMS telltale. If the telltale is not illuminated, the driver is being told that the TPMS is functioning properly and no tire is significantly under-inflated. TRW stated that, for indirect TPMSs, the ABS system already performs a system malfunction monitoring process. This includes both static and dynamic checks that are handled in a continuous monitoring process.

    The Alliance recommended that the agency not require either a bulb-check or a self-check. The Alliance stated that vehicle manufacturers include serviceability provisions as a matter of normal design practice and do not need regulatory requirements in this regard.

    After considering all the comments on this issue, the agency has decided to require a bulb-check, but not a self-check, at vehicle start-up. The agency believes that a bulb-check will add little, if any, cost to the TPMS and provide drivers with useful information, i.e., that the warning telltale bulb is functional. (73) Accordingly, the agency is adding a new section S4.3.3 as follows:

    S4.3.3 (a) Except as provided in paragraph (b) of this section, each low tire pressure warning telltale must be activated as a check of lamp function either when the key locking system is turned to the "On" ("Run") position when the engine is not running, or when the key locking system is in a position between "On" ("Run") and "Start" that is designated by the manufacturer as a check position.
    (b) The low tire pressure warning telltale need not be activated when a starter interlock is in operation.

    The agency has decided not to require that the TPMS perform a self-check. The agency agrees with RMA's comment that drivers will rely on the TPMS for tire inflation maintenance and check their tire pressure less often. However, NHTSA only requires a self-check for air bag and brake systems, i.e., major safety systems. Moreover, the agency is uncertain of the costs and benefits of requiring a self-check. (74) According to TPMS manufacturer comments, the TPMSs in service to date have shown outstanding reliability, so there appears to be little need for a requirement in this area.

    i. General Written Instructions for All TPMSs

    In the NPRM, the agency proposed that the vehicle owner's manual provide an image of the TPMS warning telltale and the following information, in English:

    When the TPMS warning light is lit, one of your tires is significantly under-inflated. You should stop and check your tires as soon as possible, and inflate them to the proper pressure as indicated on the vehicle's tire inflation placard. Driving on an under-inflated tire causes the tire to overheat and can eventually lead to tire failure. Under-inflation also reduces fuel efficiency and tire tread life, and may affect the vehicle's handling and stopping ability.

    The agency also proposed to allow each vehicle manufacturer, at its discretion, to provide additional information about the significance of the low tire pressure warning telltale and description of corrective action that should be undertaken.

    The Alliance stated that it was not opposed to the language the agency proposed. However, the Alliance recommended that the agency include additional language addressing inherent system limitations, owner/driver responsibility, and replacement tires and rims. The Alliance did not recommend any specific language.

    Advocates recommended that the agency change the first sentence to read: "When the TPMS warning light is lit, one or more of your tires are seriously under-inflated." Advocates also recommended that the agency remove the word "eventually" from the third sentence to encourage drivers to take immediate action.

    RMA recommended that the written instructions be revised to read as follows:

    When the TPMS warning light is lit, one of your tires is significantly under-inflated. You should stop and check your tires as soon as possible, and inflate them to the proper pressure as indicated on the vehicle's tire inflation placard. If checking air pressure when the tire is hot from driving, never "bleed" or reduce air pressure, as it is normal for pressures to increase above recommended cold pressures. Driving on a significantly under-inflated tire causes the tire to overheat and can eventually lead to tire failure. Under-inflation also reduces fuel efficiency and tire tread life, and may affect the vehicle's handling and stopping ability. Each tire, including the spare, should be checked monthly when cold and set to the recommended inflation pressure as specified on the vehicle placard and owner's manual.

    The agency is accepting Advocates' recommendation to add the words "or more" to the first sentence and remove the word "eventually" from the third sentence. The agency notes that activation of the low tire pressure warning telltale could signify that more than one tire is significantly under-inflated. The agency also notes that the word "eventually" could lead drivers to believe that a significantly under-inflated tire is not a potentially dangerous condition.

    The agency also is accepting the last sentence of RMA's recommended instructions. The agency has no objection to this information being added and believes it may be useful in encouraging drivers to check their tire pressure more often.

    The agency is not adopting Advocates' recommendation to change the word "significantly" in the first sentence to "seriously." The standard does not define either term. However, Section 13 of the TREAD Act refers to "significant" rather than "serious" under-inflation. Moreover, in the NPRM the agency discussed "significant" rather than "serious" under-inflation. For the sake of consistency, the agency believes the phrase "significantly under-inflated" should be used in the written instructions. The agency also is not adopting the third sentence of RMA's recommended language. The agency notes that if the low tire pressure warning telltale is lit, then one or more of the vehicle's tires is significantly under-inflated. The agency does not believe that drivers will respond to the warning telltale by reducing air pressure. Thus, that sentence is unnecessary.

    As noted above, the agency is accepting the Alliance's recommendation to add language concerning the inherent limitations of TPMSs. The agency specified the additional information vehicles certified to the one-tire, 30 percent compliance option must include in the owner's manual. That information must follow the general written instructions specified below.

    As for the Alliance's recommendation for additional language on driver responsibility and replacement tires, the agency is allowing manufacturers, at their discretion, to add additional information regarding the particular TPMS installed in the vehicle. This should allow manufacturers to add information concerning the limitations of the particular TPMS, driver responsibility, replacement tires, whether the TPMS works with the vehicle's spare tire, and how to use the reset button, if one is provided. However, any additional language should be placed after the written instructions the agency is requiring. The written instructions specified by the agency should be placed in the owner's manual, in English, as specified below:

    When the TPMS warning light is lit, one or more of your tires is significantly under-inflated. You should stop and check your tires as soon as possible, and inflate them to the proper pressure as indicated on the vehicle's tire information placard. Driving on a significantly under-inflated tire causes the tire to overheat and can lead to tire failure. Under-inflation also reduces fuel efficiency and tire tread life, and may affect the vehicle's handling and stopping ability. Each tire, including the spare, should be checked monthly when cold and set to the recommended inflation pressure as specified in the vehicle placard and owner's manual.

    j. Test Conditions

    In the NPRM, the agency proposed that each vehicle be tested at its GVWR and its lightly loaded vehicle weight (LLVW), defined as unloaded vehicle weight plus up to 400 pounds (including test driver and instrumentation). The ambient temperature would be between 0 degrees C (32 degrees F) and 40 degrees C (104 degrees F). The test road surface would be dry and smooth. The vehicle would be tested at speeds between 50 km/h (31.1 mph) and 100 km/h (62.2 mph).

    Advocates supported these proposed test conditions. RMA recommended that vehicles be tested at speeds up to 120 km/h (75 mph) to reflect real-world driving conditions. RMA argued that drivers typically travel on interstate highways at speeds of 75 mph and higher for extended periods of time. Thus, TPMSs should be tested to ensure that they function properly at highway speeds.

    The Alliance recommended several changes to the proposed test conditions. The Alliance recommended separate test conditions for direct and indirect TPMSs as follows:

    Test Conditions for Indirect TPMS:

    S5.1 Ambient temperature. The ambient temperature is between 0 C (32 F) and 40 C (104 F). The ambient temperature during the test procedure must not change more than +/- 1.5C (+/- 2.5 F).

    S5.2 Road test surface.

    S5.2.1 Test Surface Description. Tests are conducted on a dry, smooth level roadway.

    S5.2.2 Radius of Curvature. Minimum radius of curvature of 1600 mm.

    S5.2.3 Longitudinal Acceleration. Maximum longitudinal acceleration generated +/- 0.05 g at the test speeds indicated.

    S5.2.4 Gradient. The test surface has no more than a 1% gradient in the direction of testing and no more than a 2% gradient perpendicular to the direction of testing.

    S5.2.5 Pavement Friction. The road test surface produces a peak friction of coefficient of 0.9 when measured using an American Society of Testing Materials (ASTM) E1136 standard reference test tire, in accordance with ASTM Method E 1337-90, at a speed of 64.4 km/h (40 mph), without water delivery.

    S5.3 Altitude. Tests are conducted at an altitude between 0 to 500 m (0 to 1640 ft) above sea level.

    S5.4 Vehicle conditions.

    S5.4.1 Test weight. The vehicle is tested at its lightly loaded vehicle weight and at its gross vehicle weight rating without exceeding any of its gross axle weight ratings. The weights should also be evenly distributed between the left and right sides. The difference between the left and right side static corner weights should be less than 3% of the total vehicle weight.

    S5.4.2 Vehicle speed. The vehicle is tested at a speed between 50 km/h (31.1 mph) and 100 km/h (62.2 mph).

    Test Conditions for Direct TPMSs:

    The Alliance's recommended test conditions for direct TPMSs are the same as those for indirect TPMSs, with the following additions:

    S5.4 Barometric Pressure. Barometric Pressure will be recorded and the measured significantly under-inflated tire pressure threshold will be corrected using the following equation: P (adjusted threshold) = P (significantly under-inflated) = 1 Atmosphere -- Barometric Pressure. Note: 1 atmosphere = 101.3kpa (14.7 psi).

    NHTSA is not adopting the additional conditions recommended by the Alliance. The agency notes that specifications regarding radius of curvature, longitudinal acceleration, gradient, and pavement friction are useful in braking tests, but have little relevance to the testing of TPMSs. The agency also notes that changes in altitude and barometric pressure should make little difference, if any, in the outcome of these tests. The agency also does not see the need to specify that the vehicle weights should be evenly distributed and that the difference between the left and right side static corner should be less than 3 percent of the total vehicle weight. NHTSA does not specify this for braking or any other tests that need a high degree of precision and specificity.

    NHTSA also is not adopting RMA's recommended test speed. While passenger vehicles are regularly driven on interstate highways at speeds of 75 mph, those vehicles are also regularly driven at even higher speeds. The point of the test speeds is not to test the speed capability of the vehicle. Instead, the test speeds must cover a sufficient variety of driving speeds to reflect real-world usage. The agency believes that the proposed test speeds do that.

    NHTSA has decided to revise the definition of "lightly loaded vehicle weight" to make it consistent with Standard No. 135, "Passenger car brake systems." The definition now reads as follows:

    Lightly loaded vehicle weight means unloaded vehicle weight plus the weight of a mass of 180 kg (396 pounds), including test driver and instrumentation.

    These test conditions are the same for both the four-tire, 25 percent and one-tire, 30 percent compliance options.

    k. Test Procedures

    In the NPRM, the agency proposed that the vehicle's tires be inflated to the placard pressure. Then the vehicle would be driven between 50 km/h (31.1 mph) and 100 km/h (62.2 mph) for up to 20 minutes. While driving at that speed, any combination of tires (from one to four for the first alternative and from one to three for the second) would be deflated until it was significantly under-inflated. Then the elapsed time between the time that the vehicle's tire or combination of tires became significantly under-inflated and the time the low tire pressure warning telltale was illuminated would be recorded. After the telltale illuminates, pressure would be added to the tire or combination of tires that was deflated such that the tire or each of the tires was one psi below the level of significant under-inflation. Then the warning telltale would be checked to see if it remained illuminated. If the telltale remained illuminated, a manual reset would be attempted. These test procedures were to be repeated for each tire and rim combination recommended for the vehicle by the vehicle manufacturer.

    The Alliance claimed that the proposed test procedures would not allow for fair and adequate assessments of both direct and indirect TPMS performance. The Alliance recommended separate test procedures for indirect and direct TPMSs as follows:

    Test Procedures for Indirect TPMSs:

    Test Procedures for Direct TPMSs:

    NHTSA is not adopting the Alliance's recommended test procedures. The agency believes that the test procedures contained in this final rule adequately test both direct and indirect TPMSs under conditions similar to real-world conditions. The test procedures are as follows:

    S6. Test procedures.

    The test procedures recommended by the Alliance are similar to the procedures the agency is specifying in this final rule. The agency notes that separate test procedures for the two compliance options are necessary because the performance requirements are different for each option. For example, the agency must be able to test multiple combinations of under-inflated tires, including all four tires, when testing vehicles that are certified to the four-tire, 25 percent option.

    6. Lead Time

    In the NPRM, the agency noted that the TREAD Act requires that the agency publish this final rule by November 1, 2001, and that the final rule take effect not more than two years after the final rule. The agency was concerned that TPMS manufacturers would not have the production capacity to supply TPMSs to equip 16 million vehicles annually, and that vehicle manufacturers would not have adequate time to develop TPMSs for all their vehicle applications. Thus, the agency indicated that it would consider a phase-in with a compliance schedule of 35 percent for the first year (2003), 65 percent the second year, and 100 percent in the third year.

    No commenter opposed a phase-in of the TPMS requirements for light vehicles.

    The Alliance stated that the phase-in proposed by the agency is too aggressive to allow for orderly and cost-effective implementation of the requirements. The Alliance stated that the agency phase-in would jeopardize vehicle development programs, which allow for sufficient "prove-out" and implementation of new technology. The Alliance argued that TPMS technology is still relatively new and needs to be properly proved-out to avoid customer complaints and/or recalls.

    For these reasons, the Alliance recommended a four-year phase-in as follows: 15 percent of a manufacturer's affected products to be equipped with a semi- or fully-compliant TPMS in the first year; 35 percent in the second year; and 70 percent in the third year; and, in the final year, 100 percent of a manufacturer's affected products to be equipped with a fully-compliant TPMS. The Alliance noted that a semi-compliant TPMS is one that meets all but specified interface requirements, and would only be allowed during the phase-in period but not in the final year of the phase-in. The Alliance claimed that allowing semi-compliant TPMSs during the phase-in would reduce the cost of compliance considerably, as cluster and display alterations are very expensive and require a long lead time to implement. Delaying these interface requirements would allow manufacturers who have already designed and/or implemented TPMSs to receive credit for those systems before and during the phase-in.

    The agency agrees with the Alliance's comments about the pace of the phase-in. TPMS technology is still relatively new. While it has been used on a few high-end models for several years, it has not been widely implemented. Moreover, the agency remains concerned that TPMS manufacturers will not be able to produce enough systems and parts to supply 16 million vehicles annually.

    Accordingly, the agency is implementing a four-year phase-in period as follows: 10 percent of a vehicle manufacturer's affected vehicles must be equipped with a TPMS that complies with either the four-tire, 25 percent or the one-tire, 30 percent option in the first year (i.e., November 1, 2003 to October 31, 2004); 35 percent in the second year (i.e., November 1, 2004 to October 31, 2005); 65 percent in the third year (i.e., November 1, 2005 to October 31, 2006). After October 31, 2006, 100 percent of a vehicle manufacturer's affected vehicles must be equipped with a TPMS that complies with the requirements set forth in the second part of this final rule. As noted above, the agency will publish the second part of this final rule by March 1, 2005, in order to give manufacturers sufficient lead time.

    The agency believes this phase-in period allows for a sufficient prove-out of TPMS technology before widespread implementation in the first two years, followed by the last two years of aggressive implementation. The agency notes that the final rule requires fewer vehicles to comply in the first year of the phase-in (10 percent) than the Alliance recommended (15 percent). NHTSA is lowering the number of vehicles that will have to comply because the agency was unable to meet the statutory deadline of November 1, 2001.

    NHTSA also notes that since the agency is permitting manufacturers to comply with the one-tire, 30 percent option until at least October 31, 2006, manufacturers will be able to comply with current indirect TPMSs while working to improve the performance of indirect TPMSs.

    The agency is allowing carry-forward credits, but only for vehicles that are manufactured during the phase-in and comply with the four-tire, 25 percent option of the first part of this final rule. Vehicles that comply with the one-tire, 30 percent option cannot be counted for purposes of carry-forward credits.

    While the agency is not adopting the Alliance's particular recommendation to allow semi-compliant TPMSs during the phase-in, it has decided to allow compliance with an alternative set of requirements during that period. The agency believes the addition of the one-tire, 30 percent option to the first part of this final rule will provide ample time for manufacturers to complete any development needed to enable them to install either direct, improved indirect, or hybrid TPMSs in their vehicles by the time the second part of this final rule takes effect on November 1, 2006.

    The agency is adopting VSC's suggestion that the agency give small volume manufacturers until the end of the phase-in period to comply with the TPMS requirements. The agency has done this in the past when implementing a major rule.

    As with previous phase-ins, NHTSA is adopting reporting requirements to monitor the implementation of the phase-in. The agency is including the reporting requirements in 49 CFR Part 590, which currently specifies back door latch, hinge, and lock phase-in reporting requirements. Since the phase-in currently addressed by Part 590 was completed December 31, 1999, the agency is replacing the existing language with regulatory text addressing the phase-in of Standard No. 138's requirements for TPMS.


    C. Study of Effects of TPMSs That Do Not Meet a Four-Tire, 25 Percent Under-Inflation Requirement

    To help provide additional data on the performance and effectiveness of TPMSs, NHTSA plans to conduct a study comparing the tire pressures of vehicles without a TPMS to the tire pressures of vehicles equipped with a TPMS that does not meet a four-tire, 25 percent compliance option. The agency will arrange for a peer review of the study methodology and of the study results, including the safety significance of any differences in tire pressure between the two groups of vehicles. If sufficient data are available, the agency also will assess the performance and effectiveness of TPMSs that do meet a four-tire, 25 percent option. The study, which will be completed by March 1, 2004, has the following two purposes.

    1. Effect on Tire Pressure

    The study will give the agency additional information regarding the extent to which vehicles equipped with a TPMS that does not meet a four-tire, 25 percent option have tire pressures closer to the vehicle's manufacturer's recommended inflation pressure than vehicles without a TPMS.

    2.Effect on Number of Significantly Under-Inflated Tires

    The study also will give the agency additional information regarding the extent to which vehicles equipped with a TPMS that does not meet a four-tire, 25 percent option have fewer significantly under-inflated tires than vehicles without a TPMS.


    D. Part Two of the Final Rule -- November 2006 and Thereafter

    Based on the record compiled to this date, the results of the study, and any other new information (including, for example, information on the overall safety benefits of ABS) submitted to the agency, NHTSA will issue the second part of this final rule. The second part will be issued by March 1, 2005, to ensure vehicle manufacturers have sufficient lead time before November 1, 2006, when all new light vehicles must be equipped with a TPMS.

    Based on the record now before the agency, NHTSA tentatively believes that a four-tire, 25 percent requirement would best meet the TPMS mandate in the TREAD Act. Nevertheless, it is possible that the new information may be sufficient to justify a continuation of the requirements in the first part of this final rule, or even some other alternative.




    52 Under the phase-in, 10 percent of a manufacturer's affected vehicles will have to comply with one of the two compliance options the first year (vehicles manufactured between November 1, 2003 and October 31, 2004); 35 percent will have to comply the second year (between November 1, 2004 and October 21, 2005); and 65 percent will have to comply the third year (between November 1, 2005 and October 31, 2006).

    53 The agency is requiring manufacturers to irrevocably select the option to which they will certify each vehicle.

    54 As noted above, the minimum levels of pressure are the same for both compliance options.

    55 Since indirect TPMSs do not actually monitor tire pressure, they must be told when the vehicle's tires have been re-inflated. Thus, indirect TPMSs require the driver to push a reset button after re-inflating the vehicle's tires.

    56 The agency also notes that the issue of direct vs. indirect TPMSs was not before Congress when the bill that became the TREAD Act was being considered.

    57 This sort of legislative history is not entitled to much, if any, weight.

    58 49 CFR Part 568.3 defines "incomplete vehicle" as "an assemblage consisting, as a minimum, of frame and chassis structure, power train, steering system, suspension system, and braking system, to the extent that those systems are to be part of the completed vehicle, that requires further manufacturing operations, other than the addition of readily attachable components, such as mirrors or tire and rim assemblies, or minor finishing operations such as painting, to become a completed vehicle."

    59 Standard No. 110 specifies requirements for tire selection to prevent tire overloading.

    60 These tables, contained in the T&RA yearbook, establish the load carrying capacity of a tire at a specific inflation pressure.

    61 The indirect TPMS is manufactured by Continental Teves for the BMW M3. In the testing, it was able to detect when one, two (only if diagonally opposite each other) or three tires were significantly under-inflated.

    62 As noted above, the first part of this final rule covers vehicles manufactured from November 1, 2003 to October 31, 2006. During this period, the rule's requirements will be phased in according to the following schedule: 10 percent of a manufacturer's affected vehicles the first year, 35 percent the second year, and 65 percent the third year. Beginning November 1, 2006, all affected vehicles will have to be equipped with a TPMS. These vehicles will have to comply with the requirements in the second part of this final rule. The agency will issue the second part of this final rule by March 1, 2005.

    63 Docket No. NHTSA-2000-8011. The NPRM was published at 67 FR 10049, March 5, 2002.

    64 NHTSA notes that 1 psi equals 6.9 kPa. The agency has rounded the English conversions to the nearest psi.

    65 RMA states that normal air pressure loss is approximately 1 to 2 psi per month.

    66 The agency is requiring manufacturers to irrevocably select the option to which they will certify their vehicles.

    67 As noted above, the minimum levels of pressure are the same for both compliance options.

    68 As noted above, the minimum levels of pressure are the same for both options.

    69. 69 The actual tire pressure increase due to heat appears to depend on several factors, including whether the tire is under-inflated to start with, the load on the tire, and how much braking has occurred recently. The agency believes that the maximum increase in tire pressure due to increased temperature is 4 psi.

    70 Docket No. NHTSA-2000-8011. The NPRM was published at 67 FR 10049, March 5, 2002.

    71 To prevent the telltale from being installed in a reconfigurable display, the agency is requiring that the telltale, once illuminated, remain illuminated until automatically extinguished when all of the vehicle's tires cease to be significantly under-inflated or until manually extinguished in accordance with the vehicle manufacturer's instructions.

    72 In the symbol comprehension tests, the symbols were presented on paper as 18x18 mm images. The telltales in vehicle dashboards average about 8x8 mm.

    73 The agency did not quantify the cost of a bulb-check, but the agency notes that most of the TPMSs tested by the VRTC performed a bulb-check. Since the agency used these systems in estimating the costs of this rulemaking, the cost of a bulb-check likely was already included, e.g., in the cost of the control module.

    74 The cost of a self-check for air bag and brake systems was included in the cost of the electronic control units for those systems. The agency was unable to separately estimate the cost of a self-check for those systems. Similarly, in its tear-down study of TPMSs to estimate their costs, the agency was unable to separately estimate the cost of a self-check for TPMSs.

    75 Upon stopping the vehicle, the agency may deflate the tire(s) immediately or wait until the tire(s) cool to the ambient temperature, or any time in between, e.g., when the tire(s) reach their original cold inflation pressure. The agency recognizes that deflating the tires while they are still hot would be a less stringent test than if the tires were allowed to cool down before being deflated. All vehicles must comply when the tires are warm or cold.