20mph speed limits don’t cut the number of car crashes or casualties, study finds 

Speed limits of 20mph have ‘little impact’ on crashes, casualties and driver speed, according to a new study.

Schemes to reduce road traffic speed in certain areas have become increasingly popular in the UK and parts of Europe in an attempt to improve safety.

At traffic speeds of 30-40mph, the risk of pedestrian fatalities are up to 5.5 times greater than at speeds of 20-30mph.

But a three-year study of a 20mph rollout across Belfast suggests the measure has not made much difference, except for reducing traffic volume.

Schemes to reduce road traffic speed in certain areas have become increasingly popular in the UK and parts of Europe in an attempt to improve safety

Researchers from Queen’s University Belfast, Edinburgh University and the University of Cambridge collected data on traffic collisions, casualties, driver speed and traffic volume before a 20mph limit was introduced, as well as one and three years afterwards.

Their study encompassed 76 streets in the city centre, and they compared data with that collected from nearby streets where the restrictions did not apply.

Analysis showed that when compared with the sites that had retained their speed limits, a 20mph speed limit was associated with little change in short or long-term outcomes for road traffic collisions, casualties, or driver speed.

Small reductions in road traffic collisions of 3 per cent and 15 per cent, respectively, were observed one and three years after the policy took effect. 

But there was no statistically significant difference over time, the researchers said.

Similarly, casualty rates fell by 16 per cent and 22 per cent, respectively, one and three years after implementation – but these reductions also weren’t statistically significant.

… but speed limits may save taxpayers millions, researchers say

A controversial 20mph speed limit for roads in Wales could save £100million a year as a result of reduced deaths and injuries, researchers estimated last week.

The legislation will set the default speed limit for residential roads and built-up areas at 20mph from next September, but local authorities can keep certain roads at 30mph.

Research from the Transport Research Institute at Edinburgh Napier University found the scheme will save nearly 100 lives over a decade.

It says the direct costs of introducing a ban will be £32million, but the savings in the first year alone will be three times this because less will be spent on dealing with the aftermath of accidents.

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

The only significant decrease was seen in traffic volume, with 166 fewer vehicles per week observed during the morning rush hour following the 20mph implementation.

Writing in the Journal of Epidemiology and Community Health, the researchers said: ‘Our findings showed that a city centre 20mph 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 team said previous research has suggested a 20mph speed limit should be supplemented with other interventions such as driver training, CCTV, community speed watch and police communication.

‘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 recognise that 20mph 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,’ they added.

The team said their findings are in line with separate research conducted in Belfast, which found that members of the public saw ‘little change in traffic speed following the implementation of the 20mph speed limit’.

Meanwhile, in 2017 Manchester City Council withdrew funding for a 20mph speed limits based mainly on the fact it made ‘no difference to speed or accidents’.

However, trials in Bristol and Edinburgh found significant reductions in collision rates.

The results suggest that drivers hardly slowed down at all – which could explain why the number of crashes and casualties did not improve.

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.’ 

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