Just the addition of 25-mph-speed limit signs can significantly reduce the total number of car crashes and injury crashes, according to Seattle’s Department of Transportation (SDOT).

SDOT cites the “dramatic reduction in crashes and injuries” after adding speed limit signs to several major streets. Some speed limits were lowered from 30 mph to 25 mph.

In Seattle, the speed limit in school zones and on all residential streets is 20 MPH. Of the city’s major streets, almost half now have a 25-mph speed limit.


This SDOT map shows which major streets where the speed limit has been reduced to 25 mph. Many major streets, especially outside of downtown, are still 30 mph and have much less signage. 

The reduced speed limit, and the additional signage, are components of the city’s plan to achieve the Vision Zero goal of ending traffic deaths and serious injuries on city streets by the year 2030.

Study on injury crashes in North Seattle

While the change in speed limits and increased signage is occurring throughout Seattle, SDOT released a report for a controlled study on several North Seattle streets and neighborhoods. (For their purposes, “North Seattle” seems to apply to any area north of the Lake Washington ship canal.)