David Greene, a senior researcher with ORNL's Center for Transportation Analysis, has studied fuel economy in vehicles for nearly 20 years. He has a firm grasp of the myriad statistics and cause-and-effect relationships involved in getting people and products from place to place. Mention, for instance, that the fuel economy of the freight carriers has improved, and he responds that it isn't necessarily true; perhaps on a vehicle-mile basis, but not on a ton-mile basis, where it really counts. The causes, he says, range from a shift from rail and water to motor carriers to just-in-time manufacturing, which makes timely delivery more important than carrying a full load. With that sort of depth perception, he is a widely recognized and often-cited expert in his field.
On efforts to meet the challenges posed by a burgeoning need for transportation coupled with concerns over energy supplies and environmental effects, Greene says that inventing better machines, not changing consumer behavior, has been the preferred strategy. "Because there is no concerted effort to raise fuel economy standards, subsidize alternative fuels, or raise the gasoline tax," he notes, "we have basically put all of our eggs in the long-run technological improvement basket through the Partnership for a New Generation of Vehicles.
As a researcher in ORNL's Energy Division, David Greene's world revolves around
the plethora of vehicles in the world and the ramifications of policies designed to deal
Greene has studied the implications of replacing internal combustion vehicles with electric cars and gasoline with alternative fuels such as ethanol. He notes that for the next few decades electric vehicles will contribute little to reducing carbon dioxide emissions because their batteries must be frequently recharged. The sources of electricity for recharging are mostly carbon-based fossil fuels.
Are there gasoline substitutes for vehicles that emit lower levels of carbon dioxide and other greenhouse gases? Says Greene: "We currently have the technology to easily use several alternative fuels, including ethanol, methanol, natural gas, and propane. Unfortunately, right now these fuels don't buy us much in terms of decreased greenhouse gas emissions. There are cleaner fuels around, but in each case, either the fuels or the means of using them are not widely available. At the same time, gasoline has been `reformulated' to make it cleaner, outcompeting alternative fuels in terms of cost-effectiveness.
"There are only a few fuels that we have the technology to deal with that give improvements in greenhouse gas emissions. And producing so-called clean fuels often yields little or no net benefit. For example, when ethanol is produced from grain, the result is a fairly clean-burning fuel. But current farming methods require a great deal of fossil fuel to be burned to produce and transport the grain and fertilizers and distill the alcohol in the first place. So the advantages of the end product are cancelled out by the fuel consumption necessary to provide the raw material. The same is true of efforts to produce cleaner energy sources from fossil fuels, such as deriving methanol or electricity from coal.
"Ideally, clean fuels would be derived from relatively clean sources, such as electricity generated using hydropower or hydrogen produced from water using solar photovoltaic panels. Another option would be to develop ways of producing renewable fuels, such as biomass, that require less fossil energy. Methanol's performance is as good as gasoline, but if we make it from natural gas, it doesn't do us any good from a greenhouse gas perspective.
"If we had widely available biomass fuelslike alcoholsthat were produced using a minimum of fossil fuel, we could produce a `flex-fuel' vehicle that could run on any mixture of ethanol, methanol, or gasoline, as long as the mixture contained at least 15% gasoline. These vehicles already exist; estimates of the added cost of mass producing them range from $100 to $300. This is a classic chicken and egg problemeither we don't have demand for the vehicles because we don't have the fuels, or the other way around.
So how do we get there? "In the short term," Greene says, "the government is trying to require vehicle fleets to use some of the alternative fuelseven if they don't provide much of an advantage in the production of greenhouse gases. In the long term, the government, industry, and the national labs are teaming up in the Partnership for a New Generation of Vehicles. The partnership is gradually settling on a hybrid design, hoping that a hybrid configuration will produce the best combination of performance, energy efficiency, and environmental friendliness."
Greene notes that greenhouse gas emissions are linked to the use and fuel economy of vehicles. He provides a historical perspective.
"From 1974 through 1982, in response to the Arab oil embargos, to oil price shocks, and especially to federal fuel-economy standards, the efficiency of new cars introduced to the U.S. fleet doubled. The fuel economy of new cars introduced after 1982 has not improved significantly, but the U.S. fleet's average miles per gallon continued to increase as the older cars were replaced with the newer, more-efficient ones. Even during the 1980s, greenhouse gas emissions from highway transportation increased as the growth of vehicle travel outpaced efficiency gains. By 1992, however, the new car MPG improvements had worked their way through the fleet of new and used vehicles. In 1993 and 1994 the on-road fuel efficiency of the fleet declined slightly. Urban driving and traffic congestion continue to rise, further increasing greenhouse gas emissions.
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