are generally heavier, noisier, and more powerful at lower speeds than . They are also more fuel-efficient in most circumstances and are used in heavy road vehicles, some automobiles (increasingly so for their increased over gasoline engines), ships, , and light . Gasoline engines are used in most other road vehicles including most cars, , and . Note that in , sophisticated diesel-engined cars have taken over about 45% of the market since the 1990s. There are also engines that run on , , , (LPG), , and (TVO).
While there are different types of fuel that may power cars, most rely on gasoline or diesel. The states that the average vehicle emits 8,887 grams of carbon dioxide per gallon of gasoline. The average vehicle running on diesel fuel will emit 10,180 grams of carbon dioxide. Many governments are using fiscal policies (such as or the US ) to influence vehicle purchase decisions, with a low CO2 figure often resulting in reduced taxation. may act as an incentive for the production of more efficient, hence less polluting, car designs (e.g. ) and the development of . High fuel taxes may provide a strong incentive for consumers to purchase lighter, smaller, more fuel-efficient cars, or to not drive. On average, today's cars are about 75 percent recyclable, and using recycled steel helps reduce energy use and pollution. In the United States Congress, federally mandated fuel efficiency standards have been debated regularly, passenger car standards have not risen above the 27.5 miles per US gallon (8.6 L/100 km; 33.0 mpg) standard set in 1985. Light truck standards have changed more frequently, and were set at 22.2 miles per US gallon (10.6 L/100 km; 26.7 mpg) in 2007.