Automobiles, through their total numbers, are the largest total source of urban noise. Diesel trucks are clearly the noisiest vehicles on streets and highways; they are considerably larger in size and more complex as noise sources than passenger cars. Motorcycles are quickly becoming an important part of the total vehicular noise picture. In recent years, the registration of new motorcycles has been growing at an ever increasing rate. Not only are they used increasingly as a means of transportation among certain age groups, but the mini-cycle used off the street on trails and in parks is becoming an important source of high intensity noise.