UK research found that cutting speed limits on urban roads does not significantly improve safety. The likely reason—motorists will drive the speed limit they feel most comfortable with based on road design, weather conditions, and traffic.
Belfast officials changed the speed limits to 20 mph on 76 roads in 2016. Researchers analyzed data from before and after the 20 mph limit was introduced on the same streets and compared that data with other Northern Ireland roads that retained 30 to 40 mph. They did not find any statistically significant differences in average traffic speeds and the number of accidents. One change they did find: the 20-mph roads experienced a reduction in traffic.
These findings from Queen’s University Belfast and the University of Edinburgh were published online in the Journal of Epidemiology and Community Health.
The researchers also recommended that to change driver behavior, the 20 mph limits should be combined with other measures such as:
- Driver training
- Community engagement
- Community interventions (speed watch)
- Closed-Circuit TV (CCTV) and other surveillance
- In-car Interventions such as speed limiters
- Police enforcement
- Social media marketing to increase awareness
They also stated in the report that bringing the speed limit down to 20 mph would help facilitate a culture change from the car-dominant paradigm by putting people before cars.
Cutting speed limits to 20 mph has been increasingly popular in the UK and Europe. The Welsh government has even committed to lowering speeds on all roads where cars mix with cyclists and pedestrians.
In an interview with the UK’s Evening Standard, Royal Automobile Club (RAC) road safety spokesman Simon Williams said, “The findings of this study are surprising as they appear to suggest that drivers on 20 mph roads in Belfast hardly slowed down at all, despite the lower speed limit.”
He added, “It seems there is a serious problem with compliance as we would expect that even without enforcement, average speed would drop. Consequently, the study may demonstrate a need for councils to find other ways to get drivers to slow down, whether that’s through the enforcement or modifying road design with traffic islands, well-designed speed bumps, or chicanes.”
“Our research shows drivers are less likely to comply with a lower limit if they don’t believe it’s appropriate for the type of road.”
The same paradigm has already made it across the pond. The US is not exactly at 20 mph yet, but many cities have reduced default speed limits to 25, and Detroit, Motor City itself, has become the speed hump capital of the country.
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