Executive Summary

As required by the Transportation Recall Enhancement, Accountability, and Documentation (TREAD) Act, the agency is proposing to require a Tire Pressure Monitoring System (TPMS) 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, effective in November 2003. Two 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.

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. We assume that vehicles which currently have an ABS system would use an indirect measurement system and vehicles without ABS would use a direct measurement system to meet Alternative 2.

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, while Alternative 2 would result in 24 percent of light vehicle operators being warned.

Low tire pressure may have an influence on any crash that involves braking, since low tire pressure can result in reduced stopping distance. The quantified benefits, based on reduced stopping distance, have been estimated using two sets of data. One set of data indicates that benefits would be zero or insignificant. The second set of data indicates that there would be significant benefits from reduced stopping distance. Mid-point estimates from these two sets of data are:

Annual Full Fleet Benefits of TPMS

There are unquantified benefits related to crashes caused by blowouts, stopped vehicles with flat tires, handling characteristics, and hydroplaning. An estimated 23,000 crashes and 535 fatal crashes annually involve blowouts or flat tires. Since the agency does not collect tire pressure during its crash investigations, the agency cannot estimate how many crashes are caused by the influence that low tire inflation has on blowouts, vehicle handling, and hydroplaning. Theory and limited testing show that low tire pressure has a significant impact on all of these.

There are non-quantified costs and benefits that include the extra time it takes to inflate tires more frequently, the cost to replace batteries in some direct measurement systems, potential maintenance costs of TPMS, 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 $66.33 for Alternative 1 and $30.54 for Alternative 2.

The net costs are estimated to be:

Net Costs per Vehicle (2001 Dollars)

The net costs per equivalent life saved are estimated at the 7 percent discount rate to be:

Net Cost per Equivalent Life Saved

These estimates are derived from the following:

Total Annual Costs for 16 Million Vehicles
(Millions of 2001 Dollars)

Present Discounted Value of Benefits