It seems like common sense that reducing the speed limit would reduce the number of car accidents on city streets and highways. But if you look at the statistics a little closer, it’s clear that speed limit has little impact on the frequency of car accidents, and in some cases, higher speed limits have led to even safer roads. In 2008, for example, Purdue University reported that higher speed limits in Indiana had no impact on the number of car accidents. But anecdotal evidence shows that highways and city streets react differently to higher speed limits, due partially to the existence of pedestrians and cyclists within city limits.

This is supported by the fact that the areas that have benefited from higher speed limits are relatively remote, or free of pedestrians. A 2001 study by the National Motorists Association, for example, found that Montana car accident statistics remained consistent when the daytime speed limit was lifted. And German’s Autobahn, which is often considered dangerous for not having a blanket speed limit, saw similar results. A 2008 study by the International Traffic Safety Data and Analysis Group found that Germany averages 5.5 auto deaths per 100,000 people, compared to 12 auto deaths per 100,000 people here in the United States.

But most likely, the speed limit’s impact on traffic deaths varies by location. And when it comes to city streets, reducing speed limits has been shown to improve the big picture of street safety, by reducing the chances of bicycle accidents and pedestrian accidents. In San Francisco, speed limits have been partially blamed for a string of Masonic Avenue car accidents that have caused far too many injuries and fatalities. To deal with the problem of speeding in city limits, the San Francisco Municipal Transportation Agency intends to reduce the speed limit on a few major streets from 30 miles per hour to 25 miles per hour.

“The Engineering and Traffic Survey results indicate that lowering the speed limit to 25 MPH is appropriate and justified,” said SFMTA spokesperson Paul Rose. “These reviews and changes allow us to ensure that the speed limits are where they need to be to ensure the highest level of safety for automobile drivers, cyclists, pedestrians and Muni.”

So while it’s tempting for motorists to zoom through highways and city streets to reach their destination quickly, the SFMTA has determined that this can cause unnecessary danger in city limits due to pedestrians and cyclists vulnerable to traffic accidents. Though past results have been inconclusive, I hope the speed limit reduction will have a positive impact on San Francisco street safety.

Photo credit: JaseMan