Jennifer, one of our readers, was kind enough to link to a chart (reproduced below) of the motorcycles used in the motorcycle air pollution study comparing motorcycles to cars. What jumps out immediately is the year and mileage of the sample vehicles. Of the eight bikes in the test, the newest is a 1999 BMW with 31,474 kilometers. There are 2 1998 models, 1 each 97, 96 and 95 and 2 1993 models, a Honda Shadow and a Suzuki VS800. The newest bike is almost 7 model years old, the 2 oldest are 13 years old! Also, 2 samples were 2 stroke, a 98 Yamaha YN50 scooter and a 95 Piaggio Skipper scooter, with 11k and 15k kilometers respectively. Since the test was run in 2004, subtract almost 2 years for the age of each bike, but you still have older bikes, that may or may not have been maintained well, the full study could supply details with service records.
Cars over time do not necessarily hold up to the stringent standards they were manufactured to meet so to get a truer comparison you would need to either test all new models of cars and motorcycles to see what the new models emit, or test old models of both, however, when testing older samples, how do you normalize for maintenance and mileage?
Anyone care to test the average 1993 auto for emissions? Since there are no current 2 stroke cars that I’m aware of, to say 2 stroke scooters compare to cars in any way is a bit misleading. Again, I have not yet seen the full study, however, there are a lot of questions on even this first glance and I hope any mass media coverage of this is extremely careful to point out exactly what was found rather than going for the easy headlines which the so far limited coverage of this study has done.
Update: Read part 3 on this topic.
Chart credits: Environmental Science and Technology