Amazingly, these positive changes "did not involve the introduction of any physical traffic calming measures" (https://travelwest.info/project/ee-no-185-the-effectiveness-of-a-20mph-speed-limit-intervention-on-vehicle-speeds-in-bristol).
That being said, roadway design is still understood to be the most effective way to reduce speeds; this study just suggests that the posted limit alone can have a significant impact, and that the general behaviour change from a city-wide shift is greater than reducing limits in only designated areas.
Key takeaways:
- After implementing 20mph default speeds, speeds decreased city-wide, even on streets whose limits were unaffected: "This suggests that city-wide 20 mph speed limits could be an effective strategy for reducing injuries, as it encourages safer driving behaviour that is not restricted to 20 mph roads.
- In support of a city-wide change vs. traffic-calmed zones: "Interestingly, the reductions in fatalities in Bristol are larger than the 46% reduction in London associated with the introduction of traffic-calmed 20 mph zones,...Therefore, this finding goes some way to supporting city-wide 20 mph speed limits as an intervention to reduce road injuries."; The policy recommendation that would follow from this is to implement city-wide 20 mph limits, rather than 20 mph limits in restricted areas of a city."
Sean Carlson (he/him/his)
Active and Safe Routes to School Program, Green Action Centre
