Transportation poses perhaps the world's greatest energy challenge, and presents the best example of the social and economic dynamics affecting a change to a more efficient system. This is certainly the case in the US. The US transportation sector is 97% dependent on oil and is the dominant user of oil in the US, accounting for 60% of the national demand - more than is extracted domestically (PCAST, 1997). With low gasoline prices (Figure 4.6), there is little incentive for consumers to demand more efficient vehicles. Schipper (1999) stresses the importance of fuel prices on efficiency as gasoline costs make up a large fraction of the variable costs of driving, and influence vehicle power and size, miles driven and vehicle fuel efficiency. But aided by low fuel prices, the consistent efficiency gains that manufacturers have achieved have

Figure 4.6 US gasoline prices.

not translated into more miles to the gallon but rather more safety and luxury features. Even limited efficiency standards have failed to quench consumers' desire for larger, faster, safer cars, as is evident in the popularity of sport utility vehicles (SUVs). These are not classified as cars and hence are subject to the lower light truck CAFE standard. Figure 4.7 illustrates the higher efficiency of the US vehicle fleet following the high gasoline prices of the 1970s and the recent slowdown in efficiency gains. In addition, population growth and growth in car ownership in the US continues to offset the meager efficiency gains of about 1% per year. In the US, the population of personal vehicles will likely grow from about 200 million to about 300 million during the 21st century (Ausubel et al., 1998).

One frequently mentioned technological solution to increasing fuel efficiency is the fuel cell-powered vehicle in which compressed hydrogen mixes with oxygen from the air to produce electrical current in a low-temperature chemical reaction that emits only water. This electrochemical process is potentially 20-30% more efficient than the thermodynamic process of internal combustion engines (Ausubel et al., 1998). Several manufacturers are already building prototype cars powered by fuel cells. Daimler-Chrysler plans to begin penetrating the market within 10 years, starting at about 100000 cars per year.

Fuel Rate 25-

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