Disappointed by Diesel?

A previous review of the trends in the sales and use of light-duty diesel-powered vehicles (diesel vehicles) in Europe through the mid-1990s questioned whether the shift toward diesel vehicles would yield large energy savings. The present study expands on the previous review. Although evidence still exists that diesel vehicles of a certain size have a substantial volumetric fuel economy advantage over gasoline-powered vehicles (gasoline vehicles) of a similar size (perhaps 30%, on average), average new diesel cars (including sport utility vehicles, personal vans, personal light trucks) and the stock of diesel vehicles on the road maintain a smaller efficiency advantage over gasoline vehicles, which, as of 2005, was on the order of 15% in most countries. When the higher energy content of diesel is considered, the fuel intensity advantages for new vehicles and vehicles already on the road shrink to less than 5% and 7% for new diesel vehicles and the stock of diesel vehicles, respectively. For new diesel vehicles, the net difference in the amount of carbon dioxide (CO₂) released per kilometer (the CO₂ advantage) is even less: for new cars, less than 5% in all but one country and 0%, on average, across the eight countries sampled in 2005. For the total stock of diesel vehicles on the road, diesel vehicles provide only a small reduction in emissions compared with those of gasoline vehicles. Even with normalization for the larger average size of diesel vehicles, their CO₂ advantage appears to be no more than 15% to 18% for cars of a similar size class. The findings indicate that after all factors are taken into account, diesel vehicles in Europe may provide significant fuel savings to individual drivers but probably do not provide significant national energy or CO₂ savings, on average, among the eight countries studied.