Collision data from around the world is very clear. It shows that the faster a vehicle is travelling:
- The more likely a collision will occur because the driver has less time to react, stop or avoid the collision
- The more severe an injury resulting from the collision will be
This is why we're lowering speed limits across London.
Changes to speed limits
We're lowering speed limits because if you hit someone at 30mph they're five times more likely to die than if you hit them at 20mph.
The work is part of the Mayor's Vision Zero policy which aims to see no one killed or seriously injured on our roads by 2041.
Safer speeds made a large portion of London safer for people to live, work and commute, encouraging more Londoners out of their cars to walk, cycle and use public transport. More people using healthier and more sustainable forms of travel is vital to reducing congestion and air pollution.
Give us your your views
In March 2020, we introduced a 20mph speed limit on our roads in central London. We're now lowering the speed limit by 10mph on another 140km of the roads we manage - this should be done by May 2024.
We want to hear your views before the changes are made - we'd also like your comments and experiences on the new lower speed limits once the works are complete. Work is already underway to introduce a 20mph speed limit on 28km of roads within the boroughs of Camden, Islington, Hackney, Haringey and Tower Hamlets. See details of the next locations and feed into the discussion on the Lowering speed limits discussion page.
We will closely monitor changes we make to our roads. This may include looking at possible effects on nearby roads as needed. You can see more of our work and research into reducing road danger on the Road safety data page.
The Metropolitan Police enforces speed limits across most of London's roads. We work with the police to increase their capacity to take enforcement action against drivers and riders who speed.
The Met is currently on target to be able to take action on a million speeding offences by 2024. In 2021/22, they enforced 476,685 speeding offences, an increase of 72% compared to the previous year.
Learning from collision data
We continuously monitor the impact of the Lowering Speed Limit programme, particularly to ensure, that personal injury collisions and vehicle speeds decrease. We recently released indicative findings from the central London 20mph project. At sites monitored on the Transport for London Road Network (TLRN), collisions involving a vulnerable road user decreased by 36 per cent, while collisions resulting in death or serious injury decreased by 25 per cent after speed limits were lowered.
We plan to undertake an independent analysis on all the monitoring data once three-years of collision data is available post-implementation. Until then, please note that 2022 collision data is provisional and subject to change. The data available here is as received by Transport for London. No analysis has been undertaken on the effect of travel patterns during the Covid-19 pandemic.
Collision data before and after implementation
Speed data before implementation
Speed data after implementation
Healthy Streets Mystery Shopper surveys before and after implementation
Designing for lower speeds
There are many different ways to encourage people to drive at lower speeds, but evidence shows that self-enforcing speed limits are the most successful way to reduce speeds.
A self-enforcing speed limit means that people are more likely to drive within the signed speed limit because they feel it's the easiest and safest speed to drive along that road. This is generally because of the way the road looks and has been designed.
Some of the design and engineering measures used to lower speeds are:
- Road markings
- Speed cushions
- Raising pedestrian crossings
- Widening footways for people walking
- Giving more space to people cycling
- Reallocating traffic lanes to buses
- Removing the white line in the centre of a road
- Changing the surface of the road
- Creating curves along the road that requires vehicles travelling in different directions have to slow down or give way
- Introducing more traffic islands in the centre of the road
- Placing trees, planters and parklets along the roadside or in the centre of the road
There's no 'one size fits all' approach to reducing vehicle speeds. We use different measures depending on the type of road, who uses the road and the road space available.
We've published a toolkit outlining the various speed reduction measures that can be used when designing streets in London.
It can be used by anyone seeking to make our streets safer, healthier and more attractive for walking and cycling. However, it will be of particular relevance to local authorities responsible for implementing speed reduction programmes.
We'll continue to monitor the effectiveness of these measures in lowering speeds, so we can determine if more design changes are needed.
Effect on traffic and pollution
Imperial University's evaluation of 20mph zones in London shows they have no net negative impact on exhaust emissions.
It also shows that in 20mph zones vehicles move more smoothly, with fewer accelerations and decelerations, than in 30mph zones. This smoother driving style actually reduces particulate emissions from tyre and brake wear.
We closely monitor changes we make to our roads. This may include looking at possible effects on nearby roads as needed. You can see more of our work and research to into reducing road danger on the Road danger reduction page in Publications & reports.