Although quantitatively-speaking motorcycles make up only a small proportion of total road traffic, they invariably rank first in opinion polls on noise nuisance, together with lorries. One reason for this is that they are used primarily at noise-sensitive times and in noise-sensitive places. Like lorries, therefore, motorcycles are of exceptional significance for noise abatement. In recent years, the Umweltbundesamt (Federal Office of the Environment) has had detailed research carried out into motorcycle noise emissions as part of a set of complementary research projects concerning state-of-the-art technology and further development of the noise measuring procedure. In addition, riding states, operating states and noise generation under real conditions have been registered and analyzed. The results reveal that, in road traffic, motorcycles are operated at average levels some 6 to 9 dB (A) louder than those for cars, depending on the traffic situation. There are three principal reasons for this: Firstly, less effective inlet and exhaust silencers and the absence of bodywork produce comparably higher engine and transmission noises. Secondly, engine operating speeds are substantially higher than those for cars, even given the same riding/driving behaviour. Thirdly, motorcycle engines are operated much more frequently at high engine speeds than are car engines. Noise abatement measures must take these relationships into consideration. In line with current practice, noise values determined for motorcycles according to the homologation test procedure average some 8 dB (A) more than those for cars. The measuring method generally produced realistic results. The only deficiency is that, by using "long" gear ratios and poor throttle response, favourable noise levels can be achieved under unrealistic operating conditions. This problem can be eliminated by specifying minimum accelerations.
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