Skip to Content
Streetsblog San Francisco home
Streetsblog San Francisco home
Log In
Streetsblog.net

3 Graphs That Explain Why 20 MPH Should Be the Limit on City Streets

Graph: ProPublica
A still from ProPublica's interactive graph.
false

Speed kills, especially on city streets teeming with pedestrians and cyclists.

The investigative news nonprofit ProPublica has produced an interactive graph that deftly conveys how just a few miles per hour can spell the difference between life and death when a person is struck by a motorist. ProPublica's Lena Groeger used data from the AAA Safety Foundation to chart the plummeting likelihood of survival as motorist speed increases.

The average pedestrian struck by a driver traveling at 20 mph has a 93 percent chance of surviving. For a 70-year-old, the chances are somewhat lower but still a robust 87 percent.

As Groeger puts it:

Once cars reach a certain speed (just above 20 mph), they rapidly become more deadly. According to [AAA's Brian] Tefft's data, a person is about 70 percent more likely to be killed if they’re struck by a vehicle traveling at 30 mph versus 25 mph.

In collisions at 30 miles per hour, about one in five pedestrians will not survive. For older pedestrians, the odds are significantly worse:

Graph: ProPublica
Graph: ProPublica
false

The risk of death continues to rise dramatically as speeds exceed 30 mph. At 40 mph, most older pedestrians will not survive:

Graph: ProPublica
Graph: ProPublica
false

In addition to much higher survival rates in the event of a collision, driving at slower speeds reduces stopping distances, making it easier for drivers to avoid hitting people in the first place.

These graphs are a compelling visualization of the data that undergirds campaigns like "20's Plenty" in the UK, where residents have demanded 20 mph streets to protect the most vulnerable. As of last fall, more than 14 million people in the UK lived on streets with 20 mph speed limits, according to 20's Plenty founder Rod King, and the campaign is now focused on extending the 20 mph limit to most streets in the country:

Stay in touch

Sign up for our free newsletter

More from Streetsblog San Francisco

Call to Action: Next Step to Save the Richmond-San Rafael Bridge Bike Lane

There are six lanes on the Richmond-San Rafael Bridge. Drivers still want all of them. The fight to reserve one for people not in cars continues.

May 23, 2024

Alameda Installing Unprotected Bike Lanes on Park and Webster

How many Tess Rothsteins and Maia Correias have to die in dooring crashes before Bay Area cities stop accepting door-side lanes as an acceptable solution under any circumstances?

May 23, 2024
See all posts