Cutting speed limits to 20 mph in busy areas has little impact on crashes

By Gwyn Wright via SWNS

Cutting speed limits to 20mph in busy town and city centers has little impact on road deaths or crashes, according to a new study.

Scientists say the tough rules of the road don’t even cause drivers to slow down.

However, they do lead to quieter streets with fewer cars.

The risks of pedestrian fatalities are between three and a half and five and a half times higher at 30-40mph than they are at 20-30mph, Queen’s University Belfast researchers say.

Schemes to reduce speeds to 20mph have become increasingly popular in Britain and across Europe.

However there is little evidence on their effectiveness and earlier studies have produced mixed results.

Few such studies have covered long-term outcomes, the researchers added.

For the new study, the team looked at data on road traffic collisions, casualties, driver volume and traffic speed in Belfast before, one year after and three years after 20mph speed limits were introduced in 76 streets in the city center in 2016.

They compared the data with city center streets where the restrictions didn’t apply, as well as streets in the surrounding metropolitan area and similar streets elsewhere in Northern Ireland that had all retained their speed limits of 30-40 mph.

They found a 20mph speed limit was associated with little change in short or long-term outcomes for road traffic collisions, casualties, or driver speed.

Reductions of three and 15 percent in the number of crashes were found after one and three years but there was “no statistically significant” difference over time.

Casualty rates fell by 16 and 22 percent one and three years after implementation, but these reductions “weren’t statistically significant.”

Average traffic speed fell by only 0.2 mph one year and by 0.8 mph three years after roll-out.

Weekly traffic volume fell by 57 vehicles one year after roll-out and by 71 vehicles three years after roll-out.

The largest reductions were observed during the morning rush hour between 8 A.M. and 9 A.M. when there were 166 fewer vehicles a week compared with similarly matched streets where the 20 mph speed hadn’t been applied.

A statistically significant decrease in traffic volume of 185 fewer vehicles a week was also found when comparing all sites before and three years after roll-out.

“Previous research has suggested that 20 mph speed limit interventions should be supplemented with other interventions such as driver training, social marketing, community engagement, closed-circuit television (CCTV), in-car interventions, community interventions (eg, speed watch), and police communications," said study author Professor Ruth Hunter.

“Such success may then have the capacity to facilitate an ambitious culture change that shifts populations away from the car-dominant paradigm and help us recognize that 20 mph speed limits are not simply a road safety intervention, but instead part of the fundamental reset of the way we choose our life priorities—people before cars.

“Our findings showed that a city center 20 mph intervention had little impact on long-term outcomes including road traffic collisions, casualties and speed, except for a reduction in traffic volume.

“Future 20 mph speed limit interventions should consider the fidelity [enforcement], context and scale of implementation.”

The findings were published in the Journal of Epidemiology and Community Health.