The recent article by Rolison et al.1 cites a number of studies supporting the view that high-powered motorcycles and young adults are a dangerous combination. However, their choice of the term “high-powered motorcycles” deserves some comment. First, the data they present relate not to power but to engine capacity. Langley et al.2 noted more than a decade ago that engine capacity is a poor measure of power. More recent research3 has found no relationship between increasing motorcycle engine size and crash risk, and one study4 found an inverse relationship. Many popular cruiser-style motorcycles have very large engine capacities but moderate power, and thus low power-to-weight ratios. Research suggests that it is high power-to-weight ratios, not engine capacity or power, that are associated with higher crash risks. These high power-to-weight ratios are characteristic of sport motorcycles which appear to have the highest fatality rates of all motorcycles.5,6
Second, the cut-off level of 125 cubic centimeters (cc) between low-powered and high-powered motorcycles appears to be driven by data availability rather than any accepted threshold value. Previous research7 has considered motorcycles with engine capacities greater than 499 cc to be high powered, but even this categorization is somewhat dubious, particularly in light of the emergence of larger capacity machines (≤ 650 cc) that are restricted in power output specifically to accommodate learner riders.
A volunteer paints a colorful rainbow, moon, sun, and star on the pavement of a playground for children in a public park. Printed with permission of Corbis.
Rolison et al.1 recommend that US states consider engine size restrictions for young, inexperienced motorcyclists. Based on the research cited in this letter and the existence of very high-powered motorcycles (250 cc), many jurisdictions in Australia and Europe have instead implemented restrictions based on power-to-weight values. Learner Approved Motorcycle Schemes in Australia, for example, generally restrict new riders (of any age) to motorcycles of less than 150 kilowatts per ton and 660 cc. While the effects of these restrictions has yet to be comprehensively evaluated, they may provide a more useful approach to avoiding the combination of high power and youthfulness than that recommended by Rolison et al.
References
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