Borough-wide 20mph speed limit

We announced our plans for a borough-wide 20mph speed limit in May 2020 as part of our Covid-19 response Active Travel Plan. This followed a successful and well received pilot scheme in a number of streets across the borough and in the whole of St. Helen’s and Dalgarno wards in North Kensington.

This move was subsequently confirmed in the Transport Measures to Support Recovery From Covid-19 Lockdown Key Decision in August 2020.

Traditionally, lower speed limits were seen primarily as a road safety tool. Collisions at 30mph are much more likely to result in serious injury, particularly to pedestrians, cyclists and motor cyclists, than collisions at 20mph. However, in recent years, the main arguments in support of 20mph limits have been around the idea of ‘liveability’, and of lower speed limits making our streets more attractive and amenable to walking and cycling. This view is also now supported by Central Government in its guidance to boroughs on reacting to the Covid-19 crisis with social distancing likely to continue for many months and the associated substantial impact on public transport capacity.

We do not expect to see an increase in congestion, journey times or emissions as a result of the new limit, which is already in place in other parts of central London. There is no evidence from our own pilot or from other areas that reducing the speed limit to 20mph leads to traffic moving at very low speeds (i.e. congestion).

The 20mph speed limit will eventually cover all borough managed roads – i.e. not the Red Routes which are managed by Transport for London (except the length of Earl’s Court Road between the West Cromwell Road and Old Brompton Road which is already subject to a 20mph limit).

The Experimental Traffic Order (ETO) making the 20mph limit took effect on 13 November 2020 and the limit will come into force in each road when the boundary speed limit signs and the repeater 20mph roundel road markings we are using are laid. All the signs and markings should be in place by the end of January 2021.

The 20mph ETO invites comments and representations on the new limit so there is plenty of time to give your views – up until the 1 October 2021. Please send any comments or observations you may have to .

We will review all comments received before deciding whether to make the new speed limit permanent, amend it or remove it.


Do 20mph limits actually work?

The Mayor of London’s Transport Strategy notes that lowering speeds reduces road danger because a person is five times less likely to be fatally injured if hit at 20mph than at 30mph.

As a general rule for every one mph reduction in average speed, collision frequency reduces by around five per cent. However, there are mixed views on whether 20mph limits that are not supported by physical traffic calming actually reduce speeds. Typically, 20mph speed limits without additional traffic calming measures result in modest reductions of around 1-2mph in the 85th percentile speed. Most studies look at average and 85th percentile speeds but there is very little evidence regarding the impacts of 20mph limits on the number of vehicles driving at high speeds (i.e. over 30mph).

‘After’ speed surveys in a sample of the streets in our Pilot 20mph areas showed average 85th percentile speed reductions across the board, ranging between 0.7mph and 2.8mph.

There was only one road, where in one direction only, the number of vehicles travelling over 30mph increased by one (four percent). The others all saw significant falls, ranging between 20 per cent and 60 per cent, with most of them falling somewhere in between.

It is unlikely that everyone will drive within the 20mph limit, but we do expect to see speeds fall.

How will we monitor the impacts of the pilot scheme?

We will compare traffic speeds before and after the new limit is introduced and ask residents’ opinions. We shall look at average and 85th percentile speeds, and we will also assess whether the scheme results in fewer vehicles exceeding 30mph. We will also seek residents’ views on the impacts of the lower limits.

We cannot assess the effect on collisions as there needs to be at least three years of ‘before’ and ‘after’ data – the scheme does  not exceed an 18-month timeframe.

Will this increase congestion, journey times or air pollution?

Most studies agree that the effect of a 20mph speed limit or zone is dependent on vehicle type and the nature of the road and has a mixed overall effect on emissions resulting in no significant net effect.

A steady driving speed with minimal acceleration and braking results in lower emissions. Because most vehicles will have a shorter range of speeds they are likely to accelerate and brake for less time.

Clearly a vehicle that travels at a consistent speed of 30mph will reach its destination in less time than a vehicle that travels at a consistent speed of 20mph. However, in urban road conditions, most vehicles do not travel at a consistent speed. So any increases in some journey times are likely to be very minor.

Most studies do not account for how speeding restrictions may affect people’s choices around how they travel. We think lower speed limits will create environments in which it is more pleasant to walk and cycle. We want to encourage these forms of transport in order to reduce congestion and emissions.

How will the new limit be enforced? Will there be additional speed cameras and/or speed humps? What about traffic signs?

As with existing speed limits, the new 20mph limit can be enforced only by the police using on-street officers, mobile speed cameras and fixed speed cameras. Transport for London reports that in 2018, 154,785 people were caught and penalised for speeding related offences across London, including 38,878 on 20mph limit roads.

Some people have suggested that the Council itself should use speed cameras to enforce the speed limits, but unfortunately only the police have the legal powers to use speed cameras

There are no plans to introduce physical ‘traffic calming’ measures (such as speed humps) as part of this scheme.

There will be some additional signs to implement the scheme, but we will keep them to a minimum. We will also install 20 mph road markings on the carriageway to remind drivers of the new speed limit. Feedback from our pilot scheme suggested that residents found these more effective and visible to drivers than the smaller 20 mph ‘repeater’ signs that can be difficult to see on some of our wider streets.

Will the Council benefit financially from this scheme?

The Council will gain no additional revenue as a result of this pilot scheme. As noted above, we have no powers to issue fines for speeding.

Last updated: 18 March 2021