A national sample of car diaries, collected with the National Travel Survey in 1978-79, has made it possible to make a new estimate of the effect of cool engines on fuel consumption. For the first time it has been possible to make a detailed allowance for the effect of trips which start with the engine already warm. The Report concludes that the extra fuel used, because engines are not fully warm at all times, is roughly one third of the present national consumption by cars. (A)

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