Proposals in both Europe and the United States for future reductions in vehicle noise limits can be expected to have radical effects on the design and installation of truck diesel engines. A review of published accounts of quietened trucks shows that mostly engine enclosure has been used. There are short term incentives for manufacturers to use this approach, but it is not the most cost effective solution in the long term and has numerous problems including that of maintaining noise levels throughout the service life of the vehicle. Greater incentive is needed for radical redesign of the diesel engine to make it inherently quiet and to minimise both the on-cost and the energy penalty of noise reduction.This paper develops the theoretical background to this problem. Starting from the basic characteristics of vehicle noise, a philosophy of noise control is developed and practical means of achieving the desired noise control are discussed.