As required by the Transportation Recall Enhancement, Accountability, and Documentation (TREAD) Act, the agency is requiring a Tire Pressure Monitoring System (TPMS) to be installed in all passenger cars, multipurpose passenger vehicles, trucks and buses that have a Gross Vehicle Weight Rating of 10,000 pounds or less. Four alternatives are examined in this assessment:
Alternative 1 would require that the driver be given a warning when tire pressure is 20 percent or more below the placard pressure for one to four tires.
Alternative 2 would require that the driver be given a warning when tire pressure is 25 percent or more below the placard pressure for one to three tires.
Alternative 3 would require that the driver be given a warning when tire pressure is 25 percent or more below the placard pressure for one to four tires.
Alternative 4 would require that the driver be given a warning when tire pressure is 30 percent or more below the placard pressure for one tire.
There are two basic types of TPMS, direct measurement systems that have a tire pressure sensor for each tire, and indirect measurement systems that determine tire inflation pressure from wheel speeds. We assume that a direct measurement system would be required to meet Alternative 1.
The indirect measurement systems are designed for use with the anti-lock brake system (ABS) and compare the relative wheel speed of one wheel to another. Wheel speed correlates to tire pressure since the diameter of a tire goes down slightly with low tire pressure. Since the indirect measurement system compares relative wheel speed, it cannot determine when all four tires lose air at about the same rate, thus Alternative 2 would require a warning when one to three tires lose pressure. Commenters to the docket indicated that current indirect measurement systems could not meet Alternative 2.
TRW stated that an indirect measurement system supplemented with direct tire pressure measurement in two wheels could meet Alternative 2. The agency believes such a “hybrid” system could also meet Alternative 3. For this alternative we assume that vehicles which currently have an ABS system would use a hybrid measurement system (indirect system with two direct tire pressure measurements) and vehicles without ABS would use a direct measurement system to meet Alternatives 2 and 3.
Alternative 4 could be met by an indirect measurement system. We assume a direct measurement system would be used by those vehicles that do not have a 4-wheel ABS system. The benefits of this analysis include those cases for which the current indirect system would provide a warning, even though a warning is not required by Alternative 4 for situations involving more than one tire.
The agency conducted a large study of tire pressure at 336 gasoline stations around the country and estimates that Alternative 1 would result in 38 percent of light vehicle operators being warned of low tire pressure, Alternative 2 would result in 24 percent of light vehicle operators being warned, Alternative 3 would result in 27.5 percent of light vehicle operators being warned, while Alternative 4 would result in 10 percent of light vehicle operators being warned when there is a problem.
Alternative 1 is examined under two assumptions. Alternative 1(a) assumes that manufacturers will supply either an interactive or continuous readout of individual tire pressures for direct systems, even though this type of system is not required. Alternative 1(b) assumes that manufacturers will supply just a warning light. The agency believes that some proportion of drivers that have an interactive or continuous readout of individual tire pressures will pay attention to this information and fill their tires with air more often than those that wait for a warning to be given. These drivers will attain higher benefits from their systems because of this capability.
Low tire pressure may have an influence on skidding and loss of control crashes, crashes resulting from flat tires and blowouts, and may influence any crash that involves braking, since low tire pressure can result in increased stopping distance. The quantified safety benefits are based on these three types of crashes. The following table shows the estimated benefits assuming that all vehicles in the fleet had a TPMS meeting that alternative.
Annual Full Fleet Benefits of TPMS
(All AIS levels)
|Alternative 1 (a)||10,611||145|
|Alternative 1 (b)||10,271||141|
There are non-quantified costs that include the extra time it takes to inflate tires more frequently. There are non-quantified benefits related to crashes caused by hydroplaning, the property damage savings from avoiding crashes or reducing delta V in non-preventable crashes, and the savings in time and congestion from avoiding crashes.
The estimated consumer cost increase for an average new vehicle would be $69.65 for Alternative 1(a), $65.84 for Alternative 1(b), $48.19 for Alternatives 2 and 3, and $33.34 for Alternative 4.
The net costs are estimated to be:
Net Costs per Vehicle
|Vehicle Costs*||Value of
|Present Value of Fuel Savings||Present Value of Tread Wear
|Alt. 1 (b)||$65.84||$40.91||$22.32||$6.90||$77.53|
* Vehicle costs could be reduced in the future as manufacturers learn how to make the systems more efficiently.
** Maintenance costs could be significantly reduced in the future if manufacturers can design a system that does not require batteries to be replaced.
*** These costs could be less in the future if manufacturers can find a way to make an indirect system meet the Alternative.
The net costs per equivalent life saved are estimated at the 7 percent discount rate to be:
Net Cost per Equivalent Life Saved
|Alternative 1 (a)||$5.1 million|
|Alternative 1 (b)||$5.3 million|
|Alternative 2||$5.8 million|
|Alternative 3||$4.3 million|
|Alternative 4||$5.8 million|
These estimates are derived from the following:
Total Annual Costs for 16 Million Vehicles
(Millions of 2001 Dollars)
|Vehicle Costs||Present Value of
|Present Value of Fuel Savings||Present Value of Tread Wear
|Alt. 1 (a)||$1,114||$655||$414||$127||$1,228|
|Alt. 1 (b)||$1,053||$655||$357||$110||$1,241|