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Status Report, Vol. 45, No. 10 | September 28, 2010 Subscribe

Federal study finding no benefit from motorcycle antilocks is flawed

A poorly designed government study of antilock brakes threatens to lock up the wheels of an effort to require this safety feature on all new motorcycles. Relying on flawed methods, the authors fail to find any significant effect on crash risk from antilocks. A broad spectrum of research by the Institute and others has found otherwise.

More than 5,000 motorcyclists were killed in crashes in 2008. Such deaths continued to grow in recent years despite an overall drop in traffic deaths. More people have started riding motorcycles, with bike registrations nearly doubling from 2000 to 2008. Given that surge, it's important to look for ways to make riding safer.

Brakes are a good place to start because stopping a motorcycle is much more complicated than stopping a car. Most motorcycles have separate controls for the front and rear brakes, and braking too hard can lock up a wheel, causing a fall. Improper braking has been shown to be a common cause of crashes. Antilocks help by automatically reducing brake pressure when a lockup is about to occur and increasing it again after traction is restored.

The National Highway Traffic Safety Administration (NHTSA) announced in its 2009-11 agenda that it was considering an antilock requirement for motorcycles. The Institute strongly urged the agency to adopt the rule and reiterated this in a recent letter to the agency, warning that the new study should be ignored because it contributes nothing reliable to what's already known about the benefits of antilock brakes on motorcycles.

The agency's own studies have shown that motorcycle antilocks reduce stopping distances on the test track. Other studies have quantified the benefits using crash reconstructions. Two recent statistical analyses from the Institute and the affiliated Highway Loss Data Institute provide even more support for motorcycle antilocks (see "Antilock brakes on motorcycles prevent crashes," March 31, 2010).

Institute researchers found that motorcycles with antilock brakes are 37 percent less likely to be involved in fatal crashes than bikes without antilocks. The researchers looked at crashes from 2003 to 2008 and measured the exposure of both types of motorcycles by looking at vehicle registrations. A separate analysis of insurance claims found that motorcycles with antilocks have 22 percent fewer damage claims per insured vehicle year than the same models without antilocks.

"There's ample evidence that motorcycle antilocks prevent crashes and save lives," says Institute president Adrian Lund. "Unfortunately, NHTSA decided to do its own study using a flawed methodology. The agency should disregard its latest findings, which only serve to muddle the issue."

NHTSA's report is an apparent response to the Institute's study of fatal crashes. The authors point out that Institute researchers weren't able to control for possible differences in the riding habits of people who buy motorcycles with antilocks compared with people whose bikes don't have the feature. But the government researchers didn't consider the Highway Loss Data Institute analysis of collision claims. This study does take into account factors known to affect crash rates including rider age and sex and a bike's location, and the findings still show a significant benefit of antilocks. Instead, the government researchers tried to solve the problem by comparing crashes that would be affected by antilocks with a control group of crashes in which antilocks are deemed irrelevant. The problem, Lund says, is that the categories are hardly clear-cut.

Agency researchers performed 2 versions of their analysis using different definitions of the control group. First, they defined this group strictly as crashes in which a motorcycle was stationary or moving very slowly. However, such crashes are so rare that, as the researchers themselves acknowledge, it's hard to draw any conclusions from them.

In the second version of NHTSA's analysis, the control group includes all crashes in which a motorcycle rider wasn't at fault but the driver of another vehicle was. In this case, the methodological problem is the inclusion of many crashes in which antilocks are anything but irrelevant. For instance, a rider going straight who has to brake suddenly to avoid hitting someone improperly turning left from the opposite lane wouldn't be at fault, although antilock brakes could save the life of a rider in this situation.

"It's hard to find many crashes in which effective braking is irrelevant," Lund says. "The agency's attempt to analyze the issue this way adds nothing to what we know about antilocks and certainly doesn't refute earlier studies showing the benefits of antilock brakes."

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