leading to a 10 percent decline in average rolling resistance is a reasonable expectation.

The monetary savings and costs to consumers of such a reduction in rolling resistance can be quantified. The two consumer expenditure items of interest to Congress are motor fuel and tires. All else being equal, a reduction in rolling resistance is certain to reduce motor fuel expenditures. At issue is how large the savings would be. Chapter 3 indicates that a 10 percent reduction in rolling resistance will cause a 1 to 2 percent reduction in fuel consumption per mile driven. The effect on tire-related expenditures is more difficult to estimate without knowing the details of how the change in rolling resistance is brought about. For example, if rolling resistance is reduced because of better tire maintenance, consumers may end up spending less on tires, because properly inflated tires will have longer wear in addition to providing better fuel economy. In contrast, if the reduction is brought about by the sale of more tires that have reduced wear life, consumers may end up spending more on tires because of the need to replace them more often.

Given the many possible ways to reduce average rolling resistance, the approach taken in this chapter is to present two plausible scenarios that illustrate the potential for impacts on tire expenditures. Under the first scenario, a greater proportion of existing tires with lower rolling resistance and a smaller proportion of existing tires with higher rolling resistance are purchased in the marketplace. Under the second, many new tire designs are introduced that achieve lower rolling resistance through changes in tire materials, particularly in tread composition.

The next section reviews how a reduction in average rolling resistance can affect consumer fuel expenditures. Most of the remainder of the chapter examines the effects on tire expenditures. The chapter concludes by considering the two consumer expenditure items together.

The estimates are developed for consumers as a whole and are presented as national annualized averages. As a group, U.S. motorists make expenditures on motor fuel and replacement tires each year. Estimates are made for how average expenditures may be affected by a reduction in replacement tire rolling resistance. From the perspective of the individual consumer, outlays on fuel and tires are made over different time horizons and in different increments. For example, a tankful of fuel is

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