Borough-wide 20mph speed limit

A 20mph speed limit is now in place on all residential streets and the majority of classified roads in the borough. We will continue to work with Transport for London and neighbouring boroughs to achieve a borough-wide 20mph limit where practical.

Benefits of 20mph roads

Reducing speeds will make our streets safer, encourage walking and cycling and help improve air quality.

Safer roads

A lower speed limit will help reduce the actual and perceived danger on the streets, and take a step towards reclaiming the streets as a social place where neighbours interact with each other and more children are encouraged to walk or cycle to school. Slower traffic speeds can enable the elderly to travel independently and safely.

Studies show that compared to 30mph, not only are the number of accidents reduced in 20mph roads, but also their severity, for example:

  • In Hammersmith and Fulham, before and after casualty monitoring (both for three year periods) for various zones showed a decrease in injuries of between 40% and 70%
  • The chance of a pedestrian sustaining a fatal injury from a collision decreases from approximately 55% at an impact speed of 30mph to 17% at an impact speed on 20mph
  • Strong evidence that 20mph zones result in speed reductions. Such zones result in a decline in speeds of about 9mph on average. Even in a worst case scenario of roads with just signs only, there is an average speed reduction of 2.5mph

Health benefits

Lower speed streets help improve physical and mental health. People are encouraged to walk and cycle more, providing a chance to exercise regularly. Air and noise pollution are also reduced at 20mph, by supporting sustainable transport and encouraging transport modal shift.


There are two main methods of speed limit enforcement - passive and active. Passive speed enforcement is achieved by changing the road environment, ranging from the minimal legal requirement of installing appropriate signage and road markings, to delivering engineering solutions consisting of various traffic calming measures. Active speed enforcement is carried out by either the police, who are responsible for enforcing all speed limits, or with the assistance of local residents who wish to take part in the Community Road Watch.

Where compliance remains an issue, we will tackle it as a road safety matter and work with the police for active enforcement, and consider new traffic calming schemes if necessary.


Ad-hoc monitoring is carried out on the road network to determine the mean traffic speed, when concerns are raised. This will allow us to have a targeted approach towards enforcement in collaboration with the police and the community, and also help us identify areas for the deployment of speed indicator devices and future road safety schemes.

Frequently Asked Questions

Will it work?

This is the first step towards reducing the speeds to 20mph on residential roads after the majority of the residents supported these proposals. We have the power to introduce a reduced speed limit of 20mph, which lays down the legal basis for the police to enforce it. Without this first step, the legal speeds will remain at 30mph.

We also have the authority to make physical modifications to the roads that discourage higher speeds, such as speed humps, road narrowing's, and various other traffic calming measures. However, such measures cannot be rolled out across the borough, not only because of the financial constraints, but also because many of the streets may not need such measures. We will be monitoring the speeds after the new 20mph speed limit is introduced, and carry out further steps as appropriate in the future to improve road safety in the borough.

The borough limit will work alongside neighbouring borough's 20mph speed limits such as Lambeth. This is expected to bring about a culture change so that it is socially unacceptable to drive over 20mph in London.

Will it affect journey times?

Changing speed from 30mph to 20mph increases travel time by 1 minute per mile, if one could drive at constant speed. However, the major delay during a typical journey is because of congestion, junctions, signals, pedestrian crossings, etc.

Will this increase street clutter?

To make 20mph speed limit legally enforceable, we need to install the necessary signage and road markings. However, we have kept the installation of new posts to a minimum by utilising existing posts and lamp columns where possible.

How is the scheme being funded?

The cost of implementing the scheme is being met by a Transport for London grant that will pay mainly for appropriate signage and road markings to inform the drivers of the new limit, and the before and after speed monitoring. There are no plans for any physical traffic calming measures like speed humps as part of this scheme.

Given the cost of a ‘slight’ classified accident alone is £22,300 (police, fire, ambulance, insurance, legal and loss of income etc.) and Wandsworth Council experiences 868 slight accidents a year, even a moderate reduction in slight collisions, say 6% (52) – which is well under the evidenced average outcome, would yield a saving of £1,161,384 meaning the cost of the scheme would pay for itself in less than a year.

It should also be noted that this excludes the average cost of a ‘serious’ classified accident at £206,517 and fatality at £1,790,203. Over the last ten years, we have unfortunately experienced two fatalities a year on average and this alone adds a cost of over £3.5m per annum to the taxpayer.

Will there be more speed bumps?

Physical measures have not been included in this scheme however we will continue to investigate and consider roads for further traffic calming where there are high levels of personal injury accidents, traffic speeds and volumes. If traffic calming is required at a particular location then a public consultation will be carried out in the normal way in a new and separate proposal. No existing traffic calming has been removed as part of the 20mph speed limit.