There is strong evidence for the road safety benefits of reducing driving speeds. According to the police, exceeding speed limits and travelling too fast for the conditions contribute to 27% of fatal collisions and 14% of collisions in which a serious injury occurred.

Perhaps contrary to expectations, fast roads are not the most dangerous. Around two thirds of the collisions in which people are killed or seriously injured occur on roads with a speed limit of 30mph or less.

We know that excess speed causes death and injury, but how can we be sure that 20mph speed limits are an effective counter-measure? Numerous UK trials and evaluations have established the positive effects of 20mph limits.

• In extensive trials across 97 villages and towns in the Scottish Borders, starting in October 2020, 85% of drivers dropped their speed by 3 mph. The trial also showed that the largest speed reductions were observed in locations where higher speeds had been seen in the past – with those areas seeing an average reduction of 5.4 mph. The change in behaviour was sustained – it was still there 8 months after the start of the trial.
• In Calderdale, a 20mph limit led to a 30% reduction in casualties over a 3 year period.
• In Warrington there was a 25% reduction in injury collisions compared to the previous 18 months.
• In London, across a range of sites, collisions involving vulnerable road users decreased by 36% (from 453 to 290).

Even relatively small reductions in average speed dramatically increase survival rates for pedestrians, particularly children and the elderly.
The annual toll of pedestrian deaths and injuries in Britain (2022) is still shockingly high.

• 385 pedestrian fatalities
• 5901 serious pedestrian injuries,
• Two thirds of casualties occur on roads with a speed limit of 30mph or less

Sources

Government statistics

Scottish Borders
Napier University