VIII.   Benefits


    Following is a summary of the benefits associated with this final rule. For a more detailed analysis, see the agency's Final Economic Assessment (FEA). A copy of the FEA has been placed in the docket. In the following discussion, the agency analyzes the benefits and costs of both the four-tire, 25 percent and one-tire, 30 percent options. For purposes of this analysis, the agency assumes that 95 percent of drivers will respond to a low tire pressure warning by re-inflating their tires to the placard pressure. OMB questioned this assumption in its return letter. NHTSA has little hard evidence supporting this assumption. As discussed in the FEA, a recent study indicated that 97 percent of respondents stated they would respond to a dashboard warning light informing them that their tire pressure was low. (76) However, the agency has some concerns, such as the sample of respondents and the question format, with this study. The agency has attempted to find other studies with data on response rates to similar warning lights, but has been unable to do so.

    However, as part of the new study to be completed by March 1, 2004, the agency plans to ask owners of vehicles equipped with a TPMS whether their low tire pressure telltale has ever illuminated, and, if so, how they reacted to it. This should provide useful data for the agency's decision on the requirements for the second part of this final rule.

    Under-inflation affects many different types of crashes. These include crashes which result from:

    The agency was able to identify target populations for skidding and loss of control crashes, stopping distance (which involves any vehicle that brakes during a crash sequence), flat tires, and blowouts. The agency was not able to identify, from crash files and other reports, a target population for crashes caused by hydroplaning and overloading the vehicle.


    A. Tire Safety Benefits

    1. Skidding/Loss of Control

    Under-inflation reduces tire stiffness, which causes the tire to generate lower cornering force. When a tire is under-inflated, the vehicle requires a greater steering angle to generate the same cornering force in a curve or in a lane-change maneuver. This can result in skidding or loss of control of the vehicle in a tight curve or a quick lane-change maneuver.

    The agency estimates that if all light vehicles meet the four-tire, 25 percent compliance option, 46 fatalities will be prevented and 4,345 injuries will be prevented or reduced in severity per year due to reductions in these types of crashes. If all light vehicles meet the one-tire, 30 percent compliance option, 30 fatalities will be prevented and 2,817 injuries will be prevented or reduced in severity per year due to reductions in these types of crashes.

    2. Stopping Distance

    As explained in greater detail above in section III.D.1., "Reduced Vehicle Safety -- Tire Failures and Increases in Stopping Distance," tires are designed to maximize their performance capabilities at a specific inflation pressure. When a tire is under-inflated, the shape of its footprint and the pressure it exerts on the road surface are both altered. This degrades the tire's ability to transmit braking force to the road surface, and increases a vehicle's stopping distance, especially on wet surfaces.

    Decreasing stopping distance is beneficial in several ways. Some crashes can be completely avoided. Other crashes will still occur, but at a lower impact speed because the vehicle is able to decelerate more quickly. (77)

    The agency estimates that if all light vehicles meet the four-tire, 25 percent compliance option, 39 fatalities will be prevented and 3,410 injuries will be prevented or reduced in severity per year due to reductions in vehicles' stopping distances. If all light vehicles meet the one-tire, 30 percent compliance option, 17 fatalities will be prevented and 1,562 injuries will be prevented or reduced in severity per year due to reductions in vehicles' stopping distances.

    3. Flat Tires and Blowouts

    Under-inflation, along with high speed and overloading, can cause tire blowouts. A blowout in one of the front tires can cause the vehicle to veer off the road or into oncoming traffic. A blowout in one of the rear tires can cause spinning and loss of control of the vehicle.

    The agency estimates that if all light vehicles meet the four-tire, 25 percent compliance option, 39 fatalities will be prevented and 967 injuries will be prevented or reduced in severity per year due to reductions in crashes involving blowouts and flat tires. If all light vehicles meet the one-tire, 30 percent compliance option, 32 fatalities will be prevented and 797 injuries will be prevented or reduced in severity per year due to reductions in crashes involving blowouts and flat tires.

    4. Unquantified Benefits

    The agency cannot quantify the benefits from a reduction in crashes associated with hydroplaning and overloading vehicles. The primary reason that the agency has been unable to quantify these benefits is the lack of crash data indicating tire pressure and how often these conditions are the cause or contributing factors in a crash. The agency does not collect tire pressure in its crash investigations. NHTSA also has not been able to quantify the benefits associated with reductions in property damage and travel delays that will result from fewer crashes or reductions in the severity of crashes.


    B. Non-Tire Safety Benefits

    In its return letter, OMB stated that issuing a final rule that allowed current indirect TPMSs to comply would encourage vehicle manufacturers to install ABS on additional vehicles. OMB recommended that NHTSA consider the potential safety benefits of additional vehicles being equipped with ABS.

    However, as noted above in section VI., "Response to Issues Raised in OMB Return Letter About Preliminary Determination," there is no reliable basis for concluding that permitting current indirect TPMSs to comply would lead to a significant increase in installation of ABS in light vehicles. Moreover, there is no statistically reliable basis for concluding that ABS reduces fatalities in light vehicles. Thus, the agency does not believe that, even if vehicle manufacturers install ABS on additional vehicles, additional safety benefits would be experienced.


    C. Total Quantified Safety Benefits

    The agency estimates that the total quantified safety benefits from reductions in crashes due to skidding/loss of control, stopping distance, and flat tires and blowouts, therefore, will be 124 fatalities prevented and 8,722 injuries prevented or reduced in severity each year, if all light vehicles meet the four-tire, 25 percent compliance option; and 79 fatalities prevented and 5,176 injuries prevented or reduced in severity each year, if all light vehicles meet the one-tire, 30 percent compliance option.


    D. Economic Benefits

    1. Fuel Economy

    Correct tire pressure improves a vehicle's fuel economy. Recent data provided by Goodyear indicate that a vehicle's fuel efficiency is reduced by one percent for every 2.96 psi that its tires are below the placard pressure. The agency estimates that if all light vehicles meet the four-tire, 25 percent compliance option, vehicles' higher fuel economy will translate into an average discounted value of $16.43 per vehicle over the lifetime of the vehicle. If all light vehicles meet the one-tire, 30 percent compliance option, vehicles' higher fuel economy will translate into an average discounted value of $2.06 per vehicle over the lifetime of the vehicle.

    2. Tread Life

    Correct tire pressure also increases a tire's tread life. Data from Goodyear indicate that for every 1 psi drop in tire pressure, tread life decreases by 1.78 percent. NHTSA estimates that if all light vehicles meet the four-tire, 25 percent compliance option, average tread life will increase by 1,143 miles. If all light vehicles meet the one-tire, 30 percent compliance option, average tread life will increase by 15 miles. This will delay new tire purchases. The agency estimates that the average discounted value of these delays in tire purchases will be $5.09, if all light vehicles meet the four-tire, 25 percent compliance option; and $0.65 if all light vehicles meet the one-tire, 30 percent compliance option.




    76 "Examining the Need for Cycloid's Pump: An Analysis of Attitudes and a Study of Tire Pressure and Temperature Relationships," University of Pittsburgh, Departments of Mechanical and Industrial Engineering, December 7, 2001. A copy of this study has been placed in the docket. (Docket No. NHTSA-2000-8572-209.

    77 The FEA divides the benefits from reductions in stopping distance into fatalities and injuries reduced as a result of reductions in crashes on dry surfaces and on wet surfaces. As noted above, under-inflated tires have a greater impact on stopping distance when a vehicle is on a wet surface than when a vehicle is on a dry surface. However, most crashes occur on dry surfaces. Thus, the agency estimates that more fatalities and injuries will be reduced as a result of reductions in crashes that occur on dry surfaces than crashes that occur on wet surfaces.