Search Interpretations



    Air Brake Systems, Inc.
    c/o David M. Lick, Esq.
    Loomis, Ewert, Parsley, Davis and Gotting
    232 South Capitol Avenue
    Suite 1000
    Lansing, MI 48933

    Dear Mr. Lick:

    This letter provides an interpretation of Federal Motor Vehicle Safety Standard (FMVSS) No. 121, Air Brake Systems (49 CFR 571.121) with regard to a device sold by Air Brake Systems, Inc. (ABS, Inc.) known as the MSQR-5000. It is issued pursuant to orders in Air Brake Systems, Inc. v. Mineta (E.D. Mich. No. 01-10038).


    On June 4, 2001, we sent to Mr. James Arnold of MAC Trailer Manufacturing Inc. an interpretation of Federal Motor Vehicle Safety Standard (FMVSS or Standard) No. 121, Air Brake Systems (49 CFR 571.121). MAC Trailer, a small business manufacturing semi-trailers, asked if the MSQR-5000, manufactured by ABS, Inc., could be used to satisfy the antilock brake system (ABS) requirements of FMVSS No. 121 for trailers.

    Our letter to MAC trailer explained that MAC Trailer, if it manufactured a vehicle equipped with the MSQR-5000, would be responsible for ensuring that the vehicle met all applicable standards, including Standard 121. We further stated that installation of the MSQR-5000 as an ABS would not allow a vehicle to meet the requirements of Standard 121.

    ABS, Inc. challenged the conclusions of our June 4, 2001 interpretation, and requested further consideration. ABS, Inc. has submitted additional materials to the agency for its consideration. NHTSA has considered these materials and additional information it has obtained. This letter supercedes our June 4, 2001 interpretation.

    ABS systems and the requirements of Standard 121.

    Standard 121 establishes requirements for braking systems on vehicles equipped with air brake systems. The ABS requirements of FMVSS No. 121 were incorporated into the standard by a final rule published in the Federal Register on March 10, 1995 (60 Fed. Reg. 13216). In the preamble to the final rule, the agency noted that 10 to 15 percent of heavy combination vehicle crashes involve braking-induced instability or loss of control. These crashes result in significant property damage, injury and loss of life. In order to address the safety consequences of braking related instability, NHTSA amended FMVSS No. 121 to require antilock braking systems.

    One of the primary considerations in developing the new requirements was what, at a minimum, an antilock braking system must do in order to prevent or reduce crashes. The agency determined that due to the wide range of surfaces a vehicle may encounter in normal use, an ABS system must have the ability to determine if and when a braked wheel is momentarily locked as it passes from high to low traction conditions. Because of such varying conditions, the agency determined that any ABS must be a "closed loop" system - i.e., a system that continuously monitors the rate of wheel rotation, adjusts wheel rotation when needed and reacts to ongoing changes in rotation caused by the operation of the system, by changed road surfaces, or both (60 Fed. Reg. 13217). NHTSA also determined that warning light requirements that establish a minimum level of safety are also important for reducing crashes, deaths and injuries. The warning light requirements would inform operators of an ABS malfunction and both facilitate and encourage repairs of faulty ABS systems (60 FR 13244).

    We now turn to the terms of Standard 121.

    Warning light.

    An ABS malfunction warning light is required by Sections and of Standard 121. As noted in the preamble to the final rule, for an ABS that does not require electrical power for operation, the only mandatory electrical requirement is for malfunction indicator lamps used to signal a problem in the ABS (60 FR 13227).


    An antilock brake system is defined in S4 of Standard 121 as follows:

      Antilock brake system or ABS means a portion of a service brake system that automatically controls the degree of rotational wheel slip during braking by:

      (1) Sensing the rate of angular rotation of the wheels;

      (2) Transmitting signals regarding the rate of wheel angular rotation to one or more controlling devices which interpret those signals and generate responsive controlling output signals; and

      (3) Transmitting those controlling signals to one or more modulators which adjust brake actuating forces in response to those signals.

    The opening clause of the definition states: "Antilock brake system or ABS means a portion of a service brake system that automatically controls the degree of rotational wheel slip during braking [by]:" As noted in the preamble to the final rule adopting the definition of an ABS, the agency's definition of ABS incorporated the terms set forth in Society of Automotive Engineers (SAE) publications and European regulations to reflect the attributes of antilock systems as commonly understood by the automotive industry. (60 FR 13224).

    As background, a document that addresses the topic of antilock braking systems from the standpoint of the industry as a whole is "Antilock Brake System Review" SAE J2246 (June 1992). As explained therein, "ABS is a feedback control system that attempts to maintain controlled braking under all operating conditions. This is accomplished by controlling the slip at each wheel so as to obtain optimum forces within the limits of the tire-road combination." (emphasis added). Ibid Sec 5.3 (now renumbered as 7.3). The SAE document reiterated that ABS attempts to regulate the tire-road forces during braking to follow the driver's steering and braking commands within the constraints of the tire-road traction capability. This is accomplished by controlling the wheel slip. Ibid Sec. 5.4.4 (now renumbered as 7.4.4). "If the braking capability of the tire and road is exceeded, the wheels tend to lock. It is at this time that the antilock brake system's control logic takes over the pressure regulation at the wheel in order to obtain optimum braking." (emphasis added) Ibid Sec. 5.4.5 (now renumbered as 7.4.5).

    We first address the terms in the introductory clause of the definition of ABS. "Automatically controls" means that the ABS, rather than the driver, must regulate the degree of rotational wheel slip. This is based on the meaning of the words "automatic" and "control", and is consistent with the discussion in the preamble to the rule (60 FR 13225). As the agency noted, automatic control is necessary since the driver cannot control lockup in an emergency situation. (Id.)

    Next, the "degree of rotational wheel slip" includes several terms. To begin, the term "wheel slip" is both fundamental and well established. In the context of antilock braking systems, wheel slip refers to the proportional amount of wheel/tire skidding relative to the forward motion (velocity) of the vehicle (60 FR 13225 at n. 27); for a mathematical definition see 60 FR 13261. Zero wheel slip occurs when a wheel is unbraked and free rolling. As defined in S4 of FMVSS 121, wheel lockup means 100 percent wheel slip.

    As explained in the preamble to the rule, a rolling tire generates braking and stabilizing forces. As the brakes are applied with increasing amounts of force, braking generally improves. However, at some point, the forces in the brakes exceed the grip of the tire on the road. The tire then begins to slide and the wheel rapidly goes into full lockup. The braking force at which this occurs is not fixed; it is dependent, among other things, on the characteristics of both the tire and the road. A sliding tire loses its grip in all directions. Thus, locked wheels make a vehicle unstable and lead to loss of control (See 60 FR 13261; 13278).

    To continue, in order to minimize lockup and maximize braking, an ABS must control the degree of rotational wheel slip. To control wheel slip, an ABS system automatically reduces the amount of brake application pressure (in air braked vehicles, conventionally this is done by venting air in the brake chambers to the atmosphere) to prevent or abate excessive wheel slip - including prolonged lockup. When there is wheel slip, the level of which is assessed by the ABS from the actual and recent rates of rotation of the vehicle's wheels, the brake pressure is adjusted if the amount of wheel slip is not within an acceptable range (See 60 FR 13262). An antilock system reduces, holds and reapplies, i.e. modulates, brake pressure to each controlled wheel. As a wheel approaches lockup, the control unit sends signals to the modulator device to hold or reduce the build-up of wheel brake pressure. The brake pressure must then be increased again to ensure that the wheel is not underbraked for the road surface conditions. Through these cycles, which may require reducing or applying air pressure by as much as 60 pounds per square inch or more, the degree of wheel slip is controlled. (1)

    Finally, "during braking" means during all phases of braking when antilock braking would be called upon, including incipient wheel lock and wheel lock up. In order to meet this portion of the definition, an ABS must therefore act when wheels are about to lock, when they have locked and after they have locked.

    Therefore, the introductory clause of the definition of ABS contained in Standard 121 requires that an ABS system act automatically - without any action on the part of the driver. When functioning on its own, the system must exercise control over the degree of rotational wheel slip, including 100 percent wheel slip or full lockup. Finally, a qualifying system must act during braking, including those periods where lock up is about to occur, and where full lockup has occurred.

    The definition also sets forth the means by which these requirements are to be met. I now turn to the numbered elements of the regulatory definition quoted above.

    The first numbered element of the definition is "sensing the rate of angular rotation of the wheels." This requires sensing the rate of angular wheel rotation (emphasis added). The ability to sense the rate of angular wheel rotation, not simply whether the wheel is rotating or not, is critical to meeting the requirements of the overarching introductory clause of the definition. Information about the rate of wheel rotation, relative to the forward motion of the vehicle, enables an ABS to determine if a wheel is about to lockup or has locked up. It also enables the ABS to then control (release/hold) brake pressure to enable the wheel to begin rotating again, at an appropriate level of rotational wheel slip.

    Second, with regard to the next portion of the definition, "transmitting signals regarding the rate of wheel angular rotation to one or more controlling devices which interpret those signals and generate responsive controlling output signals," we note that the preamble stated that this is necessary to ensure that lockup will be prevented or controlled for all road surfaces and under all load conditions, and also to ensure that stability is not provided at the expense of stopping distance (60 FR 13225). The amount of braking air pressure that causes lockup varies dramatically depending on road surface, vehicle loading and other factors (60 FR 13261-62). At a given time, the rate of wheel rotation is the product of all these factors; also, wheel slip can be determined from it (60 FR 13225). The remainder of the second element - that rate information be transmitted for interpretation by a control unit - is necessary to ensure that an ABS uses the rate of wheel rotation to control wheel slip and prevent lockup. Ibid.

    The third numbered element in the definition, "transmitting those controlling signals to one or more modulators which adjust brake actuating forces in response to those signals," completes the definition of a qualifying system. In order to prevent/control lockup and ensure good stopping distances under all road surface and load conditions, such a system must modulate brake pressure in response to the rate of angular rotation of the wheels relative to the vehicle's forward motion. During automatic brake control, wheel speed is constantly monitored so that the maximum braking force for the conditions can be achieved by a succession of pressure reduction, pressure-holding and pressure-reapplication phases (60 FR 13226-28).

    All of the elements of this definition are necessary to ensure that an ABS system provides the minimum level of performance required by Standard 121 for safe braking. As discussed in the preamble and appendix to the rule, an antilock system must be capable of reducing, holding and reapplying brake pressure to each controlled wheel. The wheel speed sensor monitors the rotational speed of the wheel. When a monitored wheel approaches a lockup condition, there is a sharp deceleration of the wheel and rise in wheel slip. If this exceeds threshold levels, the control unit sends signals to the modulator device to hold or reduce the build-up of wheel brake pressure until the danger of wheel lockup has passed. The brake pressure must then be increased again to ensure that the wheel is not underbraked for the road surface conditions. During automatic brake control, wheel speed is constantly monitored so that the maximum braking force is achieved (60 FR 13226). The preamble noted that all ABSs currently marketed in the United States are electronic in nature, but other systems are not precluded.

    Following issuance of the rule on March 10, 1995, William Washington, now president of ABS, Inc., challenged the rule on the grounds that the rule reflected a deliberate attempt to exclude all but electronic ABS designs, impermissibly conflicted with operational standards for commercial motor carriers, and improperly imposed design specifications rather than performance criteria. The petitioner also claimed that NHTSA failed to evaluate and disclose information regarding petitioner's mechanical alternative to electronic ABS and published false data. The petition was denied. Washington v. Department of Transportation, 84 F.3d 1222 (10th Cir. 1996).

    The MSQR-5000 and why we initially concluded that it appeared to lack one or more features that an ABS must have to meet FMVSS No. 121's definition of ABS

    The MSQR-5000, is patented as a Differential Pressure Regulator Quick Release Valve, but not as an antilock brake system or portion thereof. (2) The device is essentially a diaphragm, backed by a piston and dampened by a rubber spring, which is acted on by the air pressure in the brake lines to the brake cylinders. As promoted, the MSQR-5000 operates on the theory that wheel lockup and other unwanted conditions occurring during braking are the result of pressure spikes and pressure differentials inside the braking system caused by out-of-round brake drums and warped rotors. It does not have a warning light. A decade ago, NHTSA tested similar devices for hydraulic brake systems on passenger cars and light trucks; NHTSA observed, and the Federal Trade Commission ruled, that they did not function as an ABS. (3)

    On January 8, 1992, William Washington, president of the corporation then manufacturing the MSQR-5000, petitioned NHTSA to amend Standard 121 to require "differential pressure regulating systems." In its review of the petition, the agency reviewed a variety of materials including test reports of vehicle testing performed at the Aberdeen Proving Ground and Southwest Research Institute (SWRI). The Aberdeen Proving Ground tests, in which a variation on the MSQR-5000 (the BX-100) was tested in comparison to other devices claimed to improve brake performance, did not verify that the device produced the claimed safety benefits. (4) Similarly, tests performed at SWRI of the MSQR-5000 indicated that the phenomenon of differential pressure between brake chambers on the same axle did not exist. Based on its finding that the requested rulemaking would not produce any safety benefits and would entail significant cost, NHTSA denied the petition on July 2, 1992 (57 FR 29459).

    The agency's recent experience with the MSQR-5000 arose shortly after particular types of vehicles were required to have ABS under Standard 121. ABS, Inc., the current manufacturer of the MSQR-5000, was marketing the device as an antilock brake system that purportedly complied with the requirements of Standard 121, according to the Federal Motor Carrier Safety Administration (FMCSA). Review of ABS, Inc.'s website revealed that the device was being marketed as an ABS complying with Standard 121 and as being "excluded" from meeting the warning light requirements due to the decision rendered in Washington v. DOT - Mr. Washington's prior challenge to Standard 121.

    In January 2001, as NHTSA began to receive inquiries from vehicle manufacturers about the MSQR-5000, a consultant retained by ABS, Inc. requested a meeting that was held on February 13, 2001. At this meeting, William Washington, President of ABS, Inc., explained the operational theory of the MSQR-5000 and presented some test data. NHTSA personnel present asked for evidence of the existence of pressure pulses caused by brake drums as previous NHTSA testing on air brake systems did not reveal the existence of such pressure pulses, questioned the ability of a device that had no means to vent air pressure from the brake lines in response to a lockup situation, and indicated to Mr. Washington that ABS, Inc. should conduct proper tests on the device using qualified test facilities.

    On February 1, 2001, MAC Trailer, a small entity within the meaning of the Small Business Regulatory Enforcement Fairness Act, in the business of manufacturing semi-trailers, requested that NHTSA provide it with an opinion of whether the MSQR-5000 met the requirements of Standard 121 as represented by ABS, Inc. MAC trailer forwarded information provided to it by ABS, Inc. about the device, including a "certification" of compliance and a decal to be applied to new vehicles documenting the warning light "exclusion." The agency responded to MAC Trailer on June 4, 2001 (at which time we had not received information from ABS, Inc.). NHTSA stated that it is NHTSA's view that the installation of an MSQR-500 alone would not allow a vehicle to meet FMVSS 121's ABS requirements. NHTSA observed that the MSQR-5000 did not have the required ABS malfunction warning light and was not, as represented by ABS, Inc. "excluded" from the warning light requirement by the decision in Washington v. DOT. The agency further indicated that it did not appear that the device had one or more features required by the definition of ABS. NHTSA based its decision on promotional literature by ABS, Inc., statements by ABS, Inc. at the meeting in February 2001, NHTSA's experiences with the MSQR-5000 and similar products, its knowledge of ABS systems and the requirements of the definition in Standard No. 121.

    NHTSA's Position on Reconsideration

    NHTSA has reconsidered its interpretation in light of materials received or obtained since June 4, as well as those that we had previously obtained. We reiterate that, as Standard 121 is a vehicle standard, the vehicle manufacturer is responsible for ensuring that the ABS requirements are met. Overall, our interpretation remains that the installation of the MSQR-5000 alone would not allow a vehicle to meet FMVSS 121's ABS requirements.

    Warning Light Requirements

    Since the issuance of the MAC trailer letter, ABS, Inc. has apparently conceded the correctness of the agency's position regarding the warning light requirement. There is no dispute that the MSQR-5000 lacks a warning light. Rather than maintaining that it is "excluded" from the warning light requirement, ABS Inc. has alternatively argued that it should not be subjected to the warning light requirement and requested that NHTSA grant it an exemption. As we explained in our June 4, 2001 letter, Standard 121 applies to vehicles and not items of equipment. Therefore, NHTSA could only grant such an exemption to the manufacturer of a complete vehicle employing the MSQR-5000.

    ABS, Inc. now claims that applying FMVSS No. 121's ABS malfunction signal/indicator requirements to the MSQR-5000 is an attempt to "place a round peg in a square hole." It is ABS, Inc.'s position that these requirements are unnecessary for the MSQR-5000, since it operates solely on air pressure and does not have any electrical or electronic components. ABS argues that if the MSQR-5000 were to fail, this failure would be evidenced by the existing gauge and low pressure warning required by S5.14 and S5.15 of FMVSS No. 121.

    This is not an argument that can be entertained in an interpretation letter such as this. An interpretation applies our laws or regulations in the context of the facts in the interpretation. It is not a vehicle for granting exceptions to our rules.

    If we were to entertain ABS, Inc.'s argument, we would not adopt it. ABS, Inc. claims that "it is clear that the warning signal requirements of FMVSS 121 were drafted with electronic ABS in mind" and that "(i)n the final rule, it is clear that NHTSA contemplated use of such warning signals for electronic ABS systems." The statement that the warning signal requirements of FMVSS No. 121 were drafted with electronic ABS in mind is simply incorrect. During the rulemaking establishing the ABS requirements, the agency expressly considered whether the malfunction signal/indicator requirements should apply to vehicles equipped with non-electrical ABS. In the preamble to the final rule, NHTSA explained that a mechanical ABS would have to comply with the malfunction indicator requirements (60 FR 13246).

    ABS, Inc. also suggests that the language of S5.2.3.3(d) indicates that NHTSA contemplated that ABS systems must be electronic. The language in question specifies that a trailer's external antilock malfunction indicator lamp illuminate whenever power is supplied to the antilock brake system and there is a malfunction in the trailer's antilock system. Your understanding is incorrect. Trailers receive power from the towing vehicle, and the antilock malfunction indicator lamp is part of the trailer's antilock brake system. The requirement that a light illuminate when the trailer receives power is not a requirement that an ABS be electronic.

    ABS, Inc. also contends that an air-operated device like the MSQR-5000 does not need any malfunction warning device other than the existing low air pressure warnings. This argument assumes that the MSQR-5000, by itself, cannot fail or be incapacitated by damage. We will not assume that a mechanical device cannot fail. Indeed, as the affidavit of William Washington attests, the MSQR-5000 may be damaged in use. (Washington para. 6(g)). Moreover, failures, or malfunction caused by damage to the unit would not necessarily result in loss of vehicle brake system pressure to the point where the vehicle's low pressure warning system would activate.

    Nonetheless, as we have explained to you before, if ABS, Inc., wishes the agency to modify the ABS malfunction signal/indicator requirements of FMVSS No. 121, it may submit a petition for rulemaking under 49 CFR Part 552 seeking modification of the standard.

    Definition of ABS

    Several arguments are offered by ABS, Inc., in support of its contention that the MSQR-5000 is an ABS system for the purposes of Standard No. 121. First, ABS, Inc., contends that the affidavits it has submitted have established that the MSQR-5000 meets the definition of an ABS contained in Standard 121. Second, ABS, Inc. contends that through testing, it has established that the MSQR-5000 meets the performance requirements of Standard 121.

    In considering the contention that the MSQR-5000 meets the requirements of Standard No. 121, we note, as we have before, that Standard 121 applies to vehicles and not to equipment. Therefore, any claim made by ABS, Inc. (or any other manufacturer of equipment as opposed to vehicles) that the device meets Standard 121 is improper.

    Definitional issues

    Through affidavits, ABS, Inc. seeks to establish that the MSQR-5000 meets the definition of ABS contained in Standard 121. We note at the outset that these affidavits, as well as the arguments contained in correspondence with NHTSA, do not address the entire definition as set forth in the Standard. As observed above, the introductory clause of the definition establishes overarching characteristics of an ABS - the automatic control of the degree of rotational wheel slip during braking. The materials submitted by ABS, Inc. do not address, much less establish that the device automatically controls rotational wheel slip during braking.

    For example, Standard 121 applies to braking, including periods of incipient lockup and full lock up (100% wheel slip). ABS, Inc. has submitted materials advancing a theory that the device would satisfy parts of the definition, based on pressure pulses produced when a braked wheel is rotating. (5) ABS, Inc.'s affidavits do not address the performance of the MSQR-5000 once full wheel lockup -- 100% wheel slip -- has occurred. At lock up, the wheel, which is attached to the brake drum, does not rotate. Since the generation of the claimed pressure pulses is dependent on a rotating wheel and drum, if the wheels stop rotating due to lockup, no more "pressure pulse" signals would be produced. As a result, the device would not function. An alternative mode of operation once the "pressure pulses" have stopped is not presented or explained. (6)

    In regard to the first numbered element of the definition - sensing the rate of angular rotation of the wheels - ABS, Inc.'s affidavits indicate that the MSQR-5000 senses the rate of angular rotation of the wheels through the pressure pulses described above. The generation of these pulses depends on irregularities in brake drums, such as occur with wear. Assuming that there are such pulses, there are still questions that must be answered before this portion of the definition would be satisfied. One is whether the device would function as an ABS on a vehicle with new brake drums. New brake drums are essentially round ("out of round" by less than five-thousandths of an inch). The test data and affidavits do not address the performance of the MSQR-5000 on a vehicle with new brake drums. An ABS, Inc. consultant, Mr. Perazzola, noted that in one test of the MSQR-5000, elimination of lockup was not demonstrated due to the use of new brake shoes and drums (Perazzola II, para. 25). No further data or explanation is given. It is not shown, therefore, that new drums would provide the signal needed by the MSQR-5000.

    Second, to satisfy the definition, the rate of angular rotation must be sensed. The materials submitted by ABS, Inc. do not establish a standard number of irregularities per wheel. Thus, the input in terms of pressure pulses would not be meaningful. For the sake of discussion, consider a wheel with four irregularities per rotation and one with one irregularity per rotation. The MSQR-5000 would not sense a difference between a wheel with four pressure pulses per rotation at a given speed and another wheel with one irregularity turning at four times the given speed. Because the number of events is not known and is not the same from wheel to wheel, the device is incapable of quantifying the rate of angular wheel rotation or wheel slip. Other than Mr. Foss' analysis - which assumes without support 10 irregularities per revolution (Foss para. 20), ABS, Inc. has not provided any information on how many pulses will be available for the device to sense changes in the rate of angular wheel rotation. Without these data, it has not been shown that the device can actually sense the rate of angular rotation of the wheels.

    The second and third numbered elements of Standard 121's definition of ABS require that an ABS automatically control the degree of rotational wheel slip by:

      (2) Transmitting signals regarding the rate of wheel angular rotation to one or more controlling devices which interpret those signals and generate responsive controlling output signals; and

      (3) Transmitting those controlling signals to one or more modulators which adjust brake actuating forces in response to those signals.

    ABS, Inc submitted materials asserting that the MSQR-5000 "interprets" the "pressure pulses" it receives through the deformation of the rubber diaphragm incorporated in the device, and the subsequent movement of the piston and rubber shock absorber behind the diaphragm. This deformation is described in the affidavits and other documents as "interpretation" of the "pressure pulses." The required responsive controlling output signals are explained as being found in the waves that are produced when the piston and rubber shock absorber diaphragm rebound and create a "compensating" pressure wave. This "compensating" pressure wave purportedly travels back to the brake cylinder, which modulates brake application.

    We need not address this in detail. We observe that ABS, Inc.'s pressure wave analysis is disputed on the ground that it does not account for the physical realities of the fluid mechanics in an actual air brake system. Furthermore, it is uncorroborated by data showing the existence of the pressure wave posited. However, even under ABS, Inc.'s theory, the MSQR-5000 would not produce controlling output signals during lockup, as required. This is so because operation of the device is dependent on pulses traveling to it in order for it to create reflected pressure wave output signals. As described above, there are no such inputs and therefore no output at lock up. Second, modulators would have to adjust brake forces to control lockup. Assume that a vehicle travels from a dry concrete surface that momentarily becomes an icy surface; assume that the brake application on the concrete involves significant amounts of brake pressure. Without ABS, the wheels would lock (due to excess brake pressure on an icy surface) and stay locked until the driver reacted. The task of the ABS system is to relieve the excess brake pressure conditions and modulate the pressure application whenever the actuation level is too high, whether the excess is 1 psi or 100 psi. As a matter of standard practice, ABS in air-braked vehicles releases the excess pressure by venting air into the atmosphere. If the MSQR-5000 reacts to incipient lockup as described in the affidavit of Mr. Foss, the offsetting pressure wave would be on the order of magnitude of 2 psi. Nothing that ABS, Inc., has submitted indicates that a 2 psi pressure differential would prevent or relieve lockup in a conventionally air braked vehicle. ABS, Inc., has not provided data showing that the MSQR-5000 device would relieve significant over-pressure conditions that occur during braking data. The materials also do not provide any information indicating if outgoing "control" pulses are affected by incoming "data" pulses, when both travel in the same brake lines.

    Vehicle Testing

    Our analysis must proceed on the assumption that the vehicle tests submitted by ABS, Inc. are intended to be the equivalent of tests performed by vehicle manufacturers to establish ABS functioning and compliance . In so doing, we note that the information on January 9 and February 13, 2001 tests provided by ABS, Inc. represents only segments of the performance tests required to establish compliance with Standard 121 and would not, by themselves, constitute sufficient documentation of compliance. Moreover, the test reports that have been provided are inadequate and incomplete.

    Three test reports have been provided to NHTSA. Even though they were submitted to show the effectiveness of the MSQR-5000, none of them compares the performance of the test vehicle with the MSQR-5000 device disabled to performance of a vehicle with the device enabled. Each reveals that they were performed without any observance of Standard 121's test procedures or accepted industry protocols in the case of the split coefficient test. (7) We have prepared charts, placed in the record, outlining the requirements of Standard 121, the Standard 121 test procedure, and SAE J46, an industry standard for split coefficient tests, with the three tests submitted by ABS, Inc. In addition, the attached Affidavits of Alfred Beier, Duane Perrin, Robert Ervin and Jeffrey Woods address the performance and value of these tests.

    The first of the tests is a stopping distance test. This January 9, 2001 test contains a number of omissions. We note first that the unbraked control trailer required by S6.1.10 of Standard 121 was not used. Instead, a standard highway van trailer was used. The report is not complete. It is not known if the trailer brakes were employed. The brakes themselves were old, unburnished, and their temperature unknown. No information on vehicle loads is given although vehicle loading is critical to evaluating brake and ABS performance. Speed data were collected through the use of an observer in the cab monitoring the speedometer - an unreliable method of measuring speed.

    The February 13, 2001 braking in a curve test contains similar omissions. In braking in curve tests, which are designed to evaluate ABS performance on low friction surfaces, establishing the characteristics of the test surface is critical. Standard 121 S5.3.6.1 specifies that the test must be performed on a curved wet roadway with a peak coefficient of friction of 0.5 as determined by use of an ASTM E1136 standard reference tire in accordance with ASTM measurement method E1337-90 at a speed of 40 mph. The test report states that the approximate coefficient of friction used was 0.5, apparently derived through use of E1337-90 tires. No record of the speed during these measurements is recorded. To simulate a panic stop, Standard 121 requires that this test be run with a full treadle brake application - an application in which, according to the definition in Standard 121, within 0.2 seconds after brake application is initiated, at least 85 psi is reached in the treadle valve's output circuits or maximum pedal travel is reached. (8) The test report indicates simply that "maximum peddle effort" was used without providing any data on the rate of application or the pressure of the application. The Standard 121 test procedure requires that this full treadle brake application be initiated 60 feet after the test vehicle enters the curved test lane. Braking was initiated in the February 13 test when approximately 28 feet into the test lane. The test report is silent in regards to the loading of the vehicle, while Standard 121 requires that the test be performed in a loaded and unloaded condition. Finally, the condition of the test vehicle's brakes and braking system are not noted. If the brakes were impaired to the point where braking force was reduced, non-compliant vehicle could successfully complete the test.

    Although the Standard 121 test procedures do not specify a split coefficient test, an examination of an industry standard test protocol, SAE J46, provides guidance on testing to produce the requisite data. SAE J46 requires split coefficient tests to be performed on a test surface where the "high" coefficient surface has twice the friction of the low surface, requires that test runs be made with the ABS activated and deactivated, requires the test course to be run in two directions, and sets minimum requirements for brake condition to ensure that braking effort is sufficient to adequately test the ABS. The SAE protocol also requires that all brake applications in all test runs be made as rapidly as possible.

    The July 9, 2001 split coefficient tests provide very little information. No data are presented on the condition of the vehicle's brakes. No measurements were made of the coefficient of friction of the high or low coefficient portions of the test surface. No data are presented comparing vehicle test runs with the MSQR-5000 enabled and disabled to show disparities in performance. It is not shown if the vehicle was run through the course in different directions. No record is presented regarding the rate of brake applications for the test stops other than a notation that in one stop, the driver "slammed" on the brakes in a simulated panic stop where the brake pressure was 40 psi. As most air braked vehicles are capable of producing brake pressures of 80 to 120 psi in a simulated panic stop, data on the particular configuration of the test vehicle is needed.

    The test data and information provided by ABS, Inc. do not establish that the MSQR-5000 device, if installed in a new vehicle, would allow that vehicle to meet the requirements of Standard 121. The device does not have, or accommodate, an ABS warning light when it is required to do so. Data presented to NHTSA to date, do not establish that a new vehicle with the MSQR-5000 would be in compliance with Standard 121, including the definition of ABS contained in the Standard. This letter does not address use of the MSQR-5000 for purposes other than as an ABS.


    John Womack
    Acting Chief Counsel

    James Arnold


    1For example, a braking vehicle may move from a high friction surface, like dry pavement, to a very low friction surface such as an icy road or a wet steel plate. In such an instance, an ABS would sense the different surfaces through changes in the rate of wheel rotation, reduce brake air line pressure by significant amounts on the low friction surface and restore it when a high friction surface is reached.

    2 NHTSA has been given an affidavit by John Cepican, a patent attorney, stating that the MSQR-5000 is an ABS under Standard 121. In our view and as indicated by the letter from the U.S. Patent Office, which is in the record, the grant of a patent for the MSQR-5000 does not establish that a device complies with regulatory requirements for an ABS.

    3The Brake-Guard, which responded to "fluctuations" caused by irregularities in drums and rotors, allegedly prevented premature wheel lock by "metering" surges and allowing brake shoes to move "reciprocally" as needed. It had been patented. Finding that the devices were not ABS systems, the FTC issued orders forbidding representations of ABS function against the manufacturers of the Brake-Guard device, In re Brake Guard Products, Inc., Docket No. 9277, 1998 FTC Lexis 184, January 23, 1998, and the manufacturers of the ABS-Traxx device, In re Automotive Breakthrough Sciences, Inc. Docket No. 9275, Federal Trade Commission, 1998 FTC Lexis 112, January 23, 1998.

    4The Aberdeen tests included both wet and dry test stops in which vehicles with the BX-100, which is identical to the MSQR-5000 except the quick release valve is mounted externally, experienced lockup at brake application pressures within the range of pressures that would be experienced in highway use.

    5As described by ABS, Inc. and its affiants, the device depends on air pressure pulses generated by irregularities in brake drums as a wheel turns for the production of signals about the rate of angular wheel rotation. Despite NHTSA requests for data documenting the existence of these pulses, they are simply said to exist or, in theory, are the inevitable product of the operation of fluid dynamics. As we have indicated before, NHTSA itself, despite extensive testing of vehicles and brakes, does not have any data indicating the pressure pulses exist. However, it is not the function of an interpretive letter to adjudicate factual issues such as this.

    6 Also, we note that mathematically, wheel slip may be expressed as the ratio of the difference between the velocity of the wheel center and the velocity of a point on the tread of the tire that is not in contact with the road, to the velocity of the wheel center. 60 FR 13260. There is nothing in ABS, Inc.'s affidavits to show that the MSQR-5000 receives or generates information about the forward velocity of the vehicle wheel center. There is nothing to show that it controls the degree of rotational wheel slip during braking.

    7 Split coefficient means that the roadway is "split" down the middle, longitudinally, and the coefficient of friction (roughly, a measure of friction or slipperiness) is different from side to side; the left-side and right-side wheels are on different surfaces. Wheels on different surfaces would reach lock up at different braking levels (see 60 FR 13278) unless controlled by an ABS.

    8 The treadle valve is linked to the driver's brake pedal. The valve sends compressed air to the brakes in proportion to the driver's input.