Collision data from around the world is very clear. It shows that the faster a vehicle is travelling:
We're introducing lower speed limits on our roads in two phases:
Many roads operated by London's boroughs, and by TfL, already have speed limits of 20mph.
Lowering traffic speeds also makes our streets less polluted, and better and safer places to walk and cycle.
The World Health Organisation advises that for roads where space is shared by motor vehicles and people walking, cycling or riding a motorbike, 20mph is the safe speed limit.
This is because a person walking who is hit by a vehicle travelling at 30mph is up to five times more likely to be killed than if they were hit at 20mph.
More and more, people are choosing to walk and cycle around London. We must reduce the risk of them being killed or seriously injured.
All roads operated by TfL in the central London Congestion Charging Zone will be 20mph. This is because of the high numbers of people walking and cycling in the area, as well as the high number of motor vehicles travelling in the area, particularly during peak periods.
Some of our roads within the central London Congestion Charging Zone are already 20mph and these include:
We've completed a risk analysis to identify roads in inner and outer London where speeds should be lowered to reduce the risk of road users being killed and seriously injured, focusing on town centres and roads with the highest risk of a collision occurring.
The risk analysis considers:
Speed limits on some of the roads within this analysis will be lowered to 20mph, while other roads might see speeds lowered from 50mph to 40mph, or from 40mph to 30mph.
The Vision Zero action plan (PDF) details this work in a chapter on Safe speeds, including a map of the roads that have been identified as high-risk. The map also shows the current and proposed speed limits.
We'll be engaging with local communities and road users about how we introduce these limits as we lower speeds across the city.
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:
There's no 'one size fits all' approach to reducing vehicle speeds. We will need to use different measures depending on the type of road, who uses the road and the road space available.
Once implemented, we'll continue to monitor the effectiveness of these measures in lowering speeds, so we can determine if more design changes are needed.
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 Safety Publications and Reports page.
The Metropolitan Police enforce all speed limits in London. They do this using on-street officers, mobile speed cameras and fixed speed cameras. In 2017/18, 155,729 people were processed for speeding related offences, including 42,771 on 20mph limit roads.
The Metropolitan Police will continue enforcing all speed limits across London, including where new speed limits are in place.