years, vehicle fuel efficiency has improved. But the efficiency gains have been offset by increases in vehicle size and performance (Lutsey and Sperling, 2005; An and DeCicco, 2007).19

Current technologies offer many fuel-economy improvements, which become increasingly attractive as fuel prices rise. Opportunities through 2020 will apply primarily to today’s vehicle fleet of spark-ignition (SI) engines, compression-ignition (CI) diesel engines, and hybrid-electric vehicles (HEVs), fueled with petroleum, biofuels, or other nonpetroleum hydrocarbon fuels. Annual incremental improvements to engines, transmissions, and nonpropulsion systems are expected to continue. During the subsequent decade, plug-in hybrid-electric vehicles (PHEVs), using electricity plus any of the above-mentioned fuels, may become a significant part of new vehicle sales. Longer-term, substantial sales of hydrogen fuel-cell vehicles (FCVs) and battery-electric vehicles (BEVs) are possible. What follows are summaries of the possible improvements in efficiency that can be expected from new technologies for LDVs.

Engine Improvements in Light-Duty Vehicles

  • Gasoline spark-ignition engines. Technologies that improve the efficiency of gasoline SI engines, such as variable valve timing, cylinder deactivation, direct injection, and turbocharging with engine downsizing, could be deployed in large numbers over the next decade. Many of these are already being produced in low volumes. They have the potential to reduce fuel consumption20 in new vehicles, on average, by about 10–15 percent in the near term (through 2020) and an additional 15–20 percent over the longer term (15–20 years). It is expected that turbocharged but downsized gasoline engines will steadily replace a significant fraction of naturally aspirated (non-turbocharged) engines.


“Fuel efficiency” relates to the amount of useful work derived from the combustion of fuel. Increased fuel efficiency can be used to improve fuel economy (vehicle-miles traveled on a gallon of fuel, for example) or to permit increases in vehicle size and performance without degrading fuel economy.


As used here, “fuel consumption” is the inverse of fuel economy—that is, the amount of fuel consumed in traveling 1 mile (or some other distance).

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