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Summer 2010 Vol. 10 Number 2

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Time to Lift the Pedal
©IMAGEZOO/SuperStockFrom the Metal

Two Reports Review Ways to Significantly Reduce Vehicle Fuel Consumption

In a move intended to reduce petroleum dependence and cut emissions of greenhouse gases, President Obama recently issued an executive order for tougher fuel efficiency standards for the nation's vehicles. Passenger vehicles will be required to meet a combined city and highway fuel economy average of 35.5 miles per gallon by 2016, and the standards may be tightened even more in the years beyond. Also, for the first time, standards are being developed to reduce fuel consumption and emissions from medium-and heavy-duty trucks.

Now vehicle manufacturers must begin working to meet these standards. Two recent reports by the National Research Council examine ways to improve fuel economy in cars and trucks.

The first of these reports, Assessment of Fuel Economy Technologies in Light-Duty Vehicles, reviewed technologies for vehicles powered by three different types of engines: conventional spark-ignition, diesel, and hybrid. Using a 2007 base vehicle, the committee that wrote the report estimated the potential fuel savings and costs to consumers of various combinations of commercially available technologies. It found that several could greatly reduce fuel consumption in passenger cars, sport utility vehicles, minivans, and other light-duty vehicles without compromising vehicle performance or safety.

But implementing these technologies will also raise vehicle purchase prices -- up to several thousand dollars per vehicle. The least expensive option would be to improve light-duty vehicles using ©Pixtal/SuperStockconventional spark-ignition engines. If a full suite of technologies were incorporated, fuel consumption could be reduced almost 30 percent compared with a 2007 base medium-sized car and pick-up truck at an additional cost of $2,200 to the consumer, the committee estimated. Even more fuel savings would result by replacing the same conventional 2007 engine with either diesel or hybrid engines and components -- as much as 37 percent to 43 percent, respectively. But vehicle purchase costs would also go up by approximately $6,000 for these options.

Both of the reports focus on fuel consumption -- the amount of fuel consumed in a given driving distance -- because energy savings are directly related to the amount of fuel used. In contrast, fuel economy measures how far a vehicle will travel on a gallon of fuel.

Because data on fuel consumption indicate money saved on fuel purchases and reductions in carbon dioxide emissions, vehicle stickers should provide consumers with fuel consumption data in addition to fuel economy information, the report says. Also, fuel economy test procedures should be revised to better reflect vehicle operating conditions and provide incentives to manufacturers to reduce fuel consumption.

The second report, Technologies and Approaches to Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles, estimates the improvements that various technologies and other approaches could achieve over the next decade in seven vehicle types. For example, using advanced diesel engines in tractor-trailers could lower their fuel consumption by up to 20 percent by 2020, and improved aerodynamics could yield an 11 percent reduction. Hybrid powertrains could lower the fuel consumption of vehicles that stop frequently, such as garbage trucks and transit buses, by as much 35 percent in the same time frame.

While the cost of making these improvements would be passed on to vehicle purchasers, the report notes that many of these suites of technologies would pay for themselves even at today's energy prices, under the committee's assumptions.

The report also provides advice on how fuel economy standards should be set. Regulators should use a measure that accounts for the amount of freight or number of passengers carried by these vehicles. The miles-per-gallon measure used to regulate the fuel economy of passenger cars is not appropriate for medium- and heavy-duty vehicles, which are designed above all to carry loads efficiently. Instead, regulation of these vehicles should use a metric that shows the efficiency with which a vehicle moves goods or passengers, such as gallons per ton-mile, a unit that reflects the amount of fuel a vehicle would use to carry a ton of goods one mile. --  Molly Galvin & Sara Frueh

Assessment of Fuel Economy Technologies for Light-Duty Vehicles. Committee on the Assessment of Technologies for Improving Light-Duty Vehicle Fuel Economy, Board on Energy and Environmental Systems, Division on Engineering and Physical Sciences (2010, 260 pp.; ISBN 0-309-15607-6). The committee was chaired by Trevor O. Jones, chair and CEO of ElectroSonics Medical Inc., Cleveland.

Technologies and Approaches to Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles. Committee to Assess Fuel Economy Technologies for Medium- and Heavy-Duty Vehicles; Board on Energy and Environmental Systems, Division on Engineering and Physical Sciences; and Transportation Research Board (2010, approx. 250 pp.; ISBN 0-309-14982-7). The committee was chaired by Andrew Brown Jr., executive director and chief technologist at Delphi Corp., Troy, Mich.

Both studies were funded by the National Highway Traffic Safety Administration.

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Copyright 2010 by the National Academy of Sciences