Taking Climate Change into Account in U.S. Transportation
Increasing the Energy Efficiency of Vehicles
In the next fifteen years, the most significant reductions in GHG emissions from U.S. transportation can be achieved by increasing the energy efficiency of vehicles. This would preserve both the desirable characteristics of conventional vehicles and the enormous investment in the infrastructure for producing, distributing, and retailing conventional petroleum fuels.
Passenger cars, light trucks, heavy-duty trucks, and commercial aircraft account for over 80 percent of U.S. transportation energy use and GHG emissions. Though not discussed here, buses, rail, marine, and pipeline modes also offer GHG emissions reduction opportunities (see Figure 2).
Click here for a larger view [1].
Light-Duty Vehicles. Light-duty vehicles (automobiles and light trucks) account for more than half of GHG emissions from the U.S. transportation sector, with emissions growing steadily. The Energy Policy and Conservation Act of 1975 mandated Corporate Average Fuel Economy (CAFE) standards for light duty vehicles. The initial round of standards in the late 1970s doubled fuel economy, but these standards have not been increased for passenger cars in over twenty years and have increased only slightly for light trucks. Because light truck standards are weaker than those for passenger cars, the shift from passenger cars to light truck purchases has led to an overall decrease in the fuel economy of new light-duty vehicles.
This trend could be reversed. Light-duty vehicle fuel economy could be increased by one-fourth to one-third at less than the cost of the fuel saved over the vehicle’s lifetime. Depending on technological progress, fuel economy could be increased by 50 to 100 percent by 2030. In the near term, improvements in engines and transmissions and in the reduction of aerodynamic drag, rolling resistance, and vehicle weight could be implemented without compromising safety, handling, or comfort. In the long term, advanced diesel engines, gasoline or diesel hybrids2 [2], and hydrogen powered fuel cell vehicles can yield more dramatic improvements.
Heavy-duty vehicles. Virtually every new large truck and bus in the United States is already equipped with the most energy-efficient internal combustion engine available, since fuel costs are typically the largest expenditure item for commercial operators after the cost of the vehicle itself. Even so, in the near term, fuel efficiency could be improved by approximately 25 percent for long-distance transport and by 50 percent for short-haul stop-and-go transport. For long-distance transport, reducing tractor-trailer idling at truck stops by installing auxiliary power units could yield fuel savings on the order of 10 percent. Reducing driving resistance3 [3] may offer even greater potential. For stop-and-go truck transport, hybrid drive trains are a promising technology. In the long term, according to the U.S. government’s 21st Century Truck program, a 140 percent improvement for medium-sized trucks, a 60 percent improvement for over-the-road tractor trailers, and a 160 percent fuel economy increase for transit buses can be achieved through a combination of engine, aerodynamic, rolling resistance, and materials technologies.4 [4]
Commercial aircraft. Major technological and operational efficiency improvements significantly reduced the energy intensity of commercial air travel in the U.S. from 1971-1998, but these gains were more than offset by the increase in air travel over the same period. Opportunities for further improvements remain, especially from improved engines and aerodynamics. Considering the time required for technology implementation and stock turnover, potential reductions in energy intensity are roughly 15 to 25 percent by 2015 and 25 to 40 percent by 2030.
Consumers, and even trucking companies, heavily discount the lifetime fuel savings of increased fuel economy. Thus, manufacturers will not produce vehicles with economically efficient fuel economy5 [5] levels, even if fuel prices increase. Governmental policies, including market based and mandatory instruments, can help overcome such behavioral factors and bring more fuel-efficient technologies into the market.
Policy options for increasing the energy efficiency of vehicles include:
- Fuel economy and GHG emissions standards and credits. Strengthening fuel economy standards or establishing GHG emissions standards would increase efficiency. Requiring light trucks such as SUVs to meet standards of equal stringency as automobiles would stop the decline in light-duty fuel economy. CAFE could also be reformed, for example, by establishing tougher standards with longer lead times, to make the program more rational and more effective. A single rulemaking with a longer lead time would result in much greater improvement than a succession of rulemakings, each with a short lead time. Vehicle manufacturers that significantly exceeded efficiency standards could be granted marketable GHG emission credits under a "cap-and-trade" law limiting GHG emissions. Another approach is to establish GHG emission standards, as is being done in California and the European Union. GHG standards would not only encourage use of low-carbon fuels, but would have the added benefits of providing automotive manufacturers more flexibility in finding least-cost means of achieving the reductions. Tire efficiency standards, especially for replacement tires, could also increase efficiency.
- Tax incentives or "feebates" for highly efficient light duty vehicles. Purchasers of highly efficient vehicles could be given tax breaks. A revenue-neutral fee and rebate ("feebate") system could be established in which fees would be paid on the purchase of inefficient vehicles and rebates provided towards the purchase of highly efficient vehicles.
- Incentives for auxiliary power units and electrical hookups at truck stops. Alternatives to truck idling could be encouraged. Several U.S. states are experimenting with an Advanced Travel Center Electrification (ATE) program,6 [6] using state funds to provide energy-efficient heating, ventilation, and cooling systems (HVAC) for use by truckers at travel centers and other areas where drivers stop and idle their vehicles. The ATE systems reduce idling and the associated fuel consumption and emissions.
- Research and development. Technology would be advanced through continuing and expanding public-private research partnerships on topics such as improving vehicle drive trains and reducing aerodynamic drag, rolling resistance, and vehicle weight. Examples include DOE’s FreedomCAR and 21st Century Truck programs, and NASA’s Ultra-Efficient Engine Technology program for aircraft.
- Information programs. Providing drivers with better information about the GHG implications of their driving choices could influence those choices. Options include driver training, more dissemination of information from sources like www.fueleconomy.gov [7], GHG emissions labels on new and used cars, and efficiency labeling for replacement tires.
NEXT: Substituting Low-Carbon Fuels for Carbon-Intensive Fuels [8]
Download PDF [9]