A new report suggests that cutting speed limits on urban roads to 20mph does not significantly improve safety in the same week as another report for the Welsh Government claimed that the policy would save lives and money.
The Welsh Government is developing plans to change the default speed limit from the current 30mph to 20mph on all roads where motorists mix with cyclists and pedestrians.
It wouldn’t mean that all roads would be at the lower limit as local councils will make the final decision in each case.
However the assumption would change, with a decision having to be made not to make a road 20mph.
The latest report, published in the Journal of Epidemiology and Community Health, analysed data from before and after the limit was introduced on 76 roads in central Belfast in 2016.
Comparisons with streets in the surrounding area and elsewhere in Northern Ireland that retained their 30mph or 40mph limit showed there were “no statistically significant differences” in terms of the number of crashes, casualty rates or average traffic speed.
Roads with a 20mph limit did experience a reduction in traffic, according to the authors of the report, who include Professor Ruth Hunter of Queen’s University Belfast and Dr Ruth Jepson of the University of Edinburgh.
The report said that 20mph limits could be combined with other measures such as driver training, CCTV and police communications to “facilitate an ambitious culture change that shifts populations away from the car-dominant paradigm”.
It added that reducing speed limits is “not simply a road-safety intervention” but can be “part of the fundamental reset of the way we choose our life priorities – people before cars”.
RAC road safety spokesman Simon Williams said: “The findings of this study are surprising as they appear to suggest that drivers on 20mph roads in Belfast hardly slowed down at all, despite the lower speed limit, which is at odds with other reports.
“It seems there is a serious problem with compliance as we would expect that even without enforcement, average speeds 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 enforcement or modifying road design with traffic islands, well-designed speed humps or chicanes.”
Mary Williams, chief executive of road safety charity Brake, described 20mph limits as “life-saving”, particularly for pedestrians and people riding bicycles and motorbikes.
She went on: “It is a matter of physics. At speeds of 20mph or less, drivers have significantly more chance to spot hazards and stop in time.
“The difference between a 20mph limit and a 30mph limit is a doubled stopping distance.”
Earlier this week another report was published based on research conducted by the Transport Research Institute (TRI) at Edinburgh Napier University, in conjunction with Public Health Wales.
It estimated that a new default 20mph speed limit on residential roads across Wales will save around £100m in the first year alone.
The new 20mph default speed limit is estimated to save more than 100 lives over a decade and 14,000 casualties in total could be avoided, according to the research.
Cardiff University academic Dr Georgina Santos told ITV Wales’ Sharp End programme that "there's no doubt" that the 20mph speed limit is a good idea.
She said: "It will definitely reduce the number of collisions - it means more time to react, more time to brake, because the braking distance will be shorter.
"We know very well that the higher the speed, the more severe the injury sustained by those involved in a collision. So not only will the number of collisions be lower - most importantly, life will be saved."
Climate Change Minister Lee Minister also told Sharp End: “The 20mph is about a broader package of change which is about making the environment more pleasant to walk and to cycle.
"Bus companies always say the biggest barriers to bus use is congestion and delays.
"What we hope will happen is that (20mph) will smooth out traffic flow - not having so much braking, starting and stopping - because people are speeding up to a set of lights and stopping again. We've all seen it happening in our own journeys to work."
The Welsh Conservatives are opposed to changing the default speed limit.
In response to the new report, their leader Andrew RT Davies said: “We have always said that introducing 20mph speed limits should be decided by local councils and implemented for specific places, such as outside of schools, hospitals and care homes.
“It is clear that, unlike what Labour Ministers would have you believe, evidence regarding the benefits of blanket implementation of a 20mph speed limit is not conclusive.
“What we do know is that, according to Labour ministers, this policy will cost the economy an astonishing £4.5bn.”