If you ever have the bad fortune to be involved in a collision as a pedestrian, your chances of survival hinge on one crucial factor: the speed the motorist was traveling.

If the driver was going 40 miles per hour, the victim has only a 15 percent chance of living. But at 20 miles per hour, the pedestrian’s odds jump to 95 percent, according to research by the United Kingdom Department for Transport.

We’ve reported before that communities across the UK have adopted a 20 mph speed limit in a campaign to protect pedestrians and cyclists called “20’s Plenty.” The concept could soon be tested in New York City.

Given the striking connection between driver speed and pedestrian safety, it’s surprising more cities haven’t followed suit. Network blog Gateway Streets examines how this concept might be applied in the city of St. Louis, where motorists are allowed to race through pedestrian-laden downtown streets at speeds as high as 35 miles per hour.

The speed limit on the majority of streets in the St. Louis CBD is 25 mph. Outside the CBD, but still within downtown, speed limits are commonly set at 30 mph. Some of the arterial roads through downtown, however, have 35 mph speed limits despite crossing major pedestrian corridors. Pedestrian safety, it seems, plays second fiddle to making sure vehicles get from one side of downtown to the other as quickly as possible.

Perhaps most baffling of all are 4th St and Memorial Drive. Thousands of tourist cross these two streets every year to access the Arch and Old Courthouse. Improved sidewalks to cross Memorial Drive and the I-70 trench were only just completed last year. Yet, the speed and volume of traffic on these streets still scream danger. The 35 mph speed limits on these streets are unacceptable. For comparison purposes, the 3-5 lane streets on either side of Fort Washington Way in downtown Cincinnati—very similar to I-70 and Memorial Drive, here—have 25 mph speed limits.

When 20 mile per hour speed limits were imposed in the UK, towns saw road fatalities drop by as much as 22 percent and safety was improved for both pedestrians and drivers. Their example provides a great framework for the city of St. Louis, as well as other cities.

Elsewhere on the Network today: Commute by Bike comments on ways employers are encouraging their employees to bike to work. The L.A. County Bicycle Coalition reports that a group of homeowners are threatening to disrupt an important Bus Rapid Transit line on Wilshire Boulevard. And Matt Yglesias argues that football stadiums belong on the outskirts of cities.