Speed limits have been reduced from 30mph in hundreds of urban areas across Britain over the past 20 years, with London imposing blanket restrictions of 20mph on all inner-city roads by 2024. But experts from Queen’s University Belfast found that although the limits reduce traffic volumes, they do little to stop accidents – mainly because they are often ignored. The team collected traffic and accident data in 2013 and 2014 in Belfast and compared it with 2017, a year after the 20mph restrictions were introduced, and 2019, three years later. The data was also compared with city center roads where the restrictions were not in place, as well as roads in the surrounding metropolitan area and similar roads elsewhere in Northern Ireland that had all retained speed limits between 30 and 40mph. Analysis of all data showed that compared to locations that had retained speed limits, a 20 mph speed limit was associated with little change in short- or long-term outcomes for traffic crashes, fatalities, or driver speed.
“Significant reduction in road traffic volume”
The average traffic speed decreased by only 0.2 mph in the first year and by 0.8 mph after three years. Ruth Hunter, professor of public health and planetary health at Queen’s University Belfast said: “We did find reductions in casualties and conflicts. However, these were generally small and we could not be sure that they were not a chance finding, so they were not statistically significant. “We have seen significant reductions in the volume of road traffic. The 20mph speed limit may have reduced traffic volume due to changes to alternative routes or a change in travel mode. “Our assessment highlights that some drivers were unaware of the 20mph speed limit intervention and that enforcement was unlikely. “Overall, the pre-implementation average speed on most roads was below 20mph, which calls into question whether a 20mph speed limit intervention was necessary in Belfast city centre.”
Reduced speed limits known to prevent fatalities
Many towns and cities have introduced reduced speed limits to prevent fatalities. At traffic speeds of 30-40 mph, the risks of pedestrian death are 3.5-5.5 times greater than at speeds of 20-30 mph. Some cities have also seen significant reductions in road traffic speed, collisions and fatalities by introducing lower speed limits, such as Edinburgh. Road deaths fell by almost a quarter and serious injuries by a third when Edinburgh reduced the speed limit to 20mph. The research was published in the Journal of Epidemiology and Community Health.
