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This paper reviews the history of heavy truck noise legislation in the U.S. Both legislative activity and the response of vehicle and engine manufacturers are described. The cost cycle experienced by manufacturers is also described. Over a period of time, the costs involved in meeting noise regulations are reduced without increasing truck noise levels. Data is presented which shows that public complaints about truck noise are often related to modified vehicle exhaust systems. The data shows that modified exhaust systems have an especially severe effect on compression brake noise. Additional results suggest that some trucks with extensively modified exhaust systems may be able to pass the in-use noise standard.

Fuel injection and cylinder pressures of diesel engines have increased substantially over the past decade, as have noise levels of many engines. Test results show that these two trends are linked: gear train impact, driven by fuel system and crankshaft torsional excitation, has become a dominant noise forcing function in heavy duty diesel engines. Fuel system torsional dampers, crank gear isolators, and rear gear trains can reduce gear impact noise. Empirical equations have been developed to predict the overall noise of heavy-duty diesel engines, based only on the size and location of the gear train. These simple equations can predict engine noise levels with surprising accuracy.