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Status Report, Vol. 43, No. 9 | October 22, 2008 Subscribe

Antilock brakes on motorcycles reduce both crash frequencies and deaths

If they need to stop on a dime, these riders will enjoy an advantage most others don't because of the antilock brakes on their motorcycle. Two new studies indicate crash reductions associated with antilocks. Both the frequency of crashes for which insurance claims are filed and the rate of fatal motorcycle crashes go down among bikes with antilock brakes.

The importance of equipping bikes with antilocks increases as motorcycling proliferates. Motorcycle sales more than tripled from 1997 to 2005. Deaths of motorcyclists have more than doubled since 1997, with some kinds of bikes having much higher death rates than others (see Status Report special issue: motorcycles, Sept. 11, 2007). About 5,000 motorcyclists died in crashes last year.

The new study of fatal motorcycle crashes was conducted by Institute researchers, while the analysis of insurance claims is by researchers at the affiliated Highway Loss Data Institute (HLDI). Adrian Lund is president of both organizations.

"Even though adding antilocks won't make motorcycling as safe as going by car, it's something manufacturers can do to reduce the risk of traveling on 2 wheels instead of 4," Lund says. "It's a way to reduce the chances of overturning a bike and crashing, so it can save lives among people who choose motorcycles for their basic transportation, to save on gasoline, or just for fun."

When antilocks are needed

Stopping a motorcycle is trickier than stopping a car. For one thing, front and rear wheels typically have separate brake controls. Both underbraking and overbraking the front and rear wheels contribute to crashes (see "California study probes causes of motorcycle crashes," June 21, 1979). In an emergency, a rider faces a split-second choice to brake hard, which can lock the wheels and cause a motorcycle to overturn, or to hold back on the brakes and risk running headlong into the emergency.

This is when antilocks can help. They reduce brake pressure when they detect impending lockup and increase the pressure again when traction is restored. Brake pressure is evaluated multiple times per second, so riders may fully brake without fear of locking the wheels.

Antilocks won't prevent every motorcycle crash. They won't help a rider who's about to be struck from behind, for example. But the new studies indicate that antilocks reduce crashes overall and save lives.

Crash reduction benefit

The HLDI study compares insurance losses under collision coverage for 12 motorcycle models with optional antilock brakes versus the same models without this option. The researchers evaluated the effects of antilock brakes on both the frequency of insurance claims that are filed for crash damage and the average cost of the damage, after accounting for rider age and gender, motorcycle age, and other factors that influence the likelihood of a crash.

Regression analysis revealed 21 percent lower insurance losses for motorcycles with antilocks, primarily because the claim frequency was 19 percent lower than for bikes without antilocks. These findings are based on a dataset of 72,000 insured years of 2003-07 model Honda, Suzuki, Triumph, and Yamaha bikes (an insured year is 1 motorcycle insured for 1 year or 2 insured for 6 months each, etc.). BMW models aren't included because it's impossible to determine from vehicle identification numbers which ones have optional antilocks and which don't. Harley-Davidsons aren't included because antilocks were added after the study years.

Antilock brakes "appear to reduce collision claims," says Matthew Moore, HLDI vice president and lead author of the study, "but they don't affect the severity of the crashes for which claims are filed. The cost of these claims doesn't go down."

Lives are being saved

In a complementary study, Institute researchers examined rates of fatal crashes of motorcycle models with and without antilocks. Eight models were studied, a subset of the 12 included in the HLDI analysis. The other 4 models were excluded because of sample size limitations.

A main finding is that there were 6.6 fatal crashes per 10,000 registered motorcycles without antilocks during 2005-06. The corresponding rate for the same bike models equipped with optional antilocks is 4.1, or 38 percent lower. Institute statistician Eric Teoh, author of the study, says the findings are statistically significant at the 90 percent confidence level.

Antilocks on cars versus motorcycles

Passenger cars began to be equipped with antilock brakes during the 1970s, after studies conducted on the test track indicated they reduce stopping distances. However, this promise didn't pan out in real-world crashes (see "Antilocks may not make the difference that many expected," Jan. 29, 1994). Antilocks didn't reduce relevant collisions.

"It isn't surprising that antilock brakes are more beneficial on motorcycles than they are on cars because the 2-wheelers are so much less stable, and it's this instability that contributes to so many crashes," Lund points out. "By reducing wheel lockup during braking, antilocks keep a lot of motorcycles from overturning."

Antilock brakes are recent additions to motorcycles. They're available almost exclusively as optional equipment, which means shoppers have to find models on which the option is offered and then pay extra for it. Antilocks were on only 18 percent of the motorcycles included in the new studies of effectiveness.

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