After initial studies, the EPA concluded that a major part of the noise problem with motorcycles was attributed to the following6-1:
- motorcycles with aftermarket exhaust systems installed, that have poor or little muffling characteristics
- owner modifications to original equipment exhaust systems (tampering)
The EPA stated that motorcycles with either modification listed above could easily increase noise emissions to over 100dba. They also realized that although motorcycles only account for two percent (2%) of total vehicular traffic mileage, because they are presently among the noisiest vehicles in the traffic stream, any reductions in motorcycle noise would have a greater impact upon overall traffic noise than what might be normally expected6-2.
The noise problem identified by the EPA in the 1970's is still prevalent, if not worse, today. The type of motorcycle (cruisers) that typically uses loud aftermarket competition use exhaust systems currently represents over fourty-five percent (45%) of new motorcycles sold today6-3, as compared to just twelve percent (12%) at the time of the EPA studies.