Subsidies and other incentives also can significantly impact the market acceptance rate of technologies that reduce fuel consumption. Finally, adoption of these technologies must play out in a sometimes unpredictable marketplace and policy setting, with changing standards for emissions and fuel economy, government incentives, consumer preferences, and other events impacting their adoption. Thus, the committee acknowledges that technologies downplayed here may play a bigger role than anticipated, or that technologies covered in this report may never emerge in the marketplace.

The timing for introducing new fuel consumption technologies may have a large influence on cost and risk. The individual vehicle models produced by automobile manufacturers pass through a product cycle that includes introduction, minor refreshments of design and features, and then full changes in body designs and power trains. To reduce costs and quality concerns, changes to reduce fuel consumption normally are timed for implementation in accordance with this process. Further, new technologies are often applied first in lower-volume, higher-end vehicles because such vehicles are better able to absorb the higher costs, and their lower volumes reduce exposure to risk. In general, 2 to 3 years is considered the quickest time frame for bringing a new vehicle model to market or for modifying an existing model. Significant carryover technology and engineering from other models or previous vehicle models are usually required to launch a new model this quickly, and the ability to significantly influence fuel consumption is thus smaller. More substantial changes to a model occur over longer periods of time. Newly styled, engineered, and redesigned vehicles can take from 4 to 8 years to produce, each with an increasing amount of new content. Further, the engine development process often follows a path separate from that for other parts of a vehicle. Engines have longer product lives, require greater capital investment, and are not as critical to the consumer in differentiating one vehicle from another as are other aspects of a car. The normal power train development process evolves over closer to a 15-year cycle, although refinements and new technologies will be implemented throughout this period. It should be noted that there are significant differences among manufacturers in their approaches to introducing new models and, due to regulatory and market pressures, product cycles have tended to become shorter over time.

Although it is not a focus of this study, the global setting for the adoption of these fuel economy technologies is critical. The two main types of internal combustion engines, gasoline spark-ignition (SI) and diesel compression-ignition (CI), are not necessarily fully interchangeable. Crude oil (which varies in composition) contains heavier fractions that go into diesel production and lighter fractions that go into gasoline. A large consumer of diesel, Europe diverts the remaining gasoline fraction to the United States or elsewhere. China is now using mostly gasoline, and so there is more diesel available globally. And automobile manufacturers and suppliers worldwide are improving their capabilities in hybrid-electric technologies. Further, policy incentives may help favor one technology over another in individual countries.


The NHTSA has a mandate to keep up-to-date on the potential for technological improvements as it moves into planned vehicular regulatory activities. It was as part of its technology assessment that the NHTSA asked the National Academies to update the 2002 National Research Council report Effectiveness and Impact of Corporate Average Fuel Economy (CAFE) Standards (NRC, 2002) and add to its assessment other technologies that have emerged since that report was prepared. The statement of task (see Appendix B) directed the Committee on the Assessment of Technologies for Improving Light-Duty Vehicle Fuel Economy to estimate the efficacy, timing, cost, and applicability of technologies that might be used over the next 15 years. The list of technologies includes diesel and hybrid electric power trains, which were not considered in the 2002 NRC report. Weight and power reductions also were to be included, but not size or power-to-weight ratio reductions. Updating the fuel economy-cost relationships for various technologies and different vehicle size classes as represented in Chapter 3 of the 2002 report was central to the study request.

The current study focuses on technology and does not consider CAFE issues related to safety, economic effects on industry, or the structure of fuel economy standards; those issues were addressed in the 2002 report. The new study looks at lowering fuel consumption by reducing power requirements through such measures as reduced vehicle weight, lower tire rolling resistance, or improved vehicle aero dynamics and accessories; by reducing the amount of fuel needed to produce the required power through improved engine and transmission technologies; by recovering some of the exhaust thermal energy with turbochargers and other technologies; and by improving engine performance and recovering energy through regenerative braking in hybrid vehicles. Additionally, the committee was charged with assessing how ongoing changes to manufacturers’ refresh and redesign cycles for vehicle models affect the incorporation of new fuel economy technologies. The current study builds on information presented in the committee’s previously released interim report (NRC, 2008).


The committee organized its final report according to broad topics related to the categories of technologies important for reducing fuel consumption, the costs and issues associated with estimating the costs and price impacts of these technologies, and approaches to estimating the fuel consumption benefits possible with combinations of these tech-

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement