Study: Seattle’s Lower Speed Limits Reduced Crash Injuries

A new study from the Insurance Institute for Highway Safety (IIHS) reveals that lowering speed limits on Seattle streets, part of the ‘Safe System’ approach that prioritizes road design and policies that limit the damage caused by human error, improved safety. “In downtown Seattle, lowering default speed limits reduced the likelihood that a crash would involve an injury by a fifth on arterial roads, IIHS researchers found. Outside of the city center, where the new limits were less consistently implemented and publicized, there were smaller injury reductions, but these were not statistically significant.”

The study credits the success in part to the city’s information campaign. “To make drivers aware of the change, the city conducted a public outreach campaign and installed gateway signs indicating the new citywide limits on arterial roads into the city, highway off-ramps and ferry terminals,” and installed new 25 mph signs on downtown arterials.

The study is the first to attempt to quantify the effect of lower speed limits on injury rates, not just on peeding. As the press release explains, “Higher speeds make crashes more likely by reducing the time a driver has to react and increasing the distance required to stop the vehicle. Higher speeds also increase the energy involved in a crash, raising the odds of an injury.”