More than half of London’s roads now carry a 20mph speed limit, with Transport for London (TfL) citing data showing the lower limit has cut deaths on borough roads by 40%, as MPs in Westminster consider whether England should adopt 20mph as the default speed limit nationally.
According to TfL’s Safe Speeds policy, speed is a factor in around half of all fatal collisions in London, and hitting someone at 30mph makes them five times more likely to die than hitting them at 20mph.
That evidence underpins the Mayor’s Vision Zero policy, which aims for no one to be killed or seriously injured on London’s roads by 2041, and has driven a steady expansion of 20mph limits across the capital over the past two decades.
Currently 166 miles of TfL’s own road network carries a 20mph limit, while two-thirds of London’s boroughs now apply the limit as policy across most of their roads.
A planned next phase aims to bring at least a further 40 miles under the limit by 2030, which would see more than 80% of roads in central and inner London carrying a 20mph limit.
The safety case behind that expansion rests on a long-term analysis of more than 150 20mph schemes introduced on borough roads between 1989 and 2013. TfL found a 40% reduction in people killed on those roads (from 15 to nine), compared with just a 7% fall in fatalities elsewhere across the borough network over the same period.
People killed or seriously injured fell by 34% (from 395 to 260) on the schemes studied, against a 15% fall across the wider network, while collisions and casualties overall dropped by 35% and 36% respectively, compared with a 12% fall elsewhere. The reduction in children killed was starker still: 75%, from four deaths to one, against no change on other roads.
TfL also pushed back on the suggestion that lower limits harm air quality, pointing to Imperial College London research showing 20mph zones have no net negative impact on exhaust emissions, and that the smoother driving style seen in 20mph zones – with fewer sharp accelerations and decelerations – actually reduces particulate emissions from tyre and brake wear compared with 30mph zones.
Enforcement has also ramped up alongside the wider rollout, with the Metropolitan Police issuing 779,440 speeding offences in 2024/25, around five times the number recorded when Vision Zero launched in 2018.
If you oppose the proposed national rollout of a blanket 20mph limit for urban areas, then London’s experience will make for uncomfortable reading.
As MCN reported in July, a panel of experts giving evidence to the House of Commons Transport Committee already testified in favour of the policy, with TfL’s own Chief Safety Officer, Lilli Matson, telling MPs that “making the policy on 20mph clear and default in urban areas would be probably the most important thing that they need to lead on.”
Transport planner Phil Jones, formerly head of the Welsh Government’s 20mph task force, argued opposition to Wales’s own default limit had been overstated, pointing to a petition against the change that gathered over 400,000 signatures when it was introduced, compared with just 2378 signatures on an identical petition two years later.
Not everyone backs a blanket national approach. IAM RoadSmart’s Director of Policy and External Communications, Nicholas Lyes, told MCN that while early evidence from Wales looked positive, “authorities should be using 20mph limits where they believe it will have the biggest impact on reducing serious co…