Speed humps

Speed humps and speed cushions help slow down people driving and support safer streets. We typically see about a 20% reduction in speeds when we install speed cushions on arterial streets.  

What’s the difference between speed humps and speed cushions? 

Speed humps go all the way across the street, and speed cushions have cutouts.  
We typically install speed humps on residential streets.  
We install speed cushions on arterial streets to accommodate emergency vehicles and Metro buses (their wheels can straddle the cushions) and we install cushions on non-arterials that have a steep slope to accommodate drainage.  

Example speed hump in Rainier Beach; Photo credit: Anna Zivarts

Example speed cushion by Hawthorne Elementary; Photo credit: SDOT

How does SDOT decide where to install speed humps, cushions, or tables?

• SDOT installs speed humps and speed cushions on neighborhood greenways and streets around schools.
• The Neighborhood Traffic Calming Program prioritizes locations for speed humps, traffic circles, and other traffic calming devices throughout the city each year.
• The Vision Zero Arterial Traffic Calming Program prioritizes the highest severity crash locations for speed cushions and other traffic calming devices.

Speed matters 

Speed plays a major role in how serious a crash is. A person walking, rolling, or biking has a much better chance of surviving a crash at lower vehicle speeds. 

In collisions, pedestrians face an 18% risk of severe injury when struck at 20 mph, a 50% risk at 30 mph, and an 81% risk at 40 mph.