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 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 supported by central government and the most recent Department for Transport advice to local authorities, which states that “20mph speed limits are being more widely adopted as an appropriate speed limit for residential roads and many through streets in built-up areas. 20mph limits alone will not be sufficient to meet the needs of active travel, but in association with other measures, reducing the speed limit can provide a more attractive and safer environment for walking and cycling.”

View more information on the GOV.UK website.

The 20mph speed limit covers all borough managed roads. The only remaining 30mph limits in Kensington and Chelsea are on some of the Red Routes, which are managed by Transport for London (TfL). The section of Earl’s Court Road between the West Cromwell Road and Old Brompton Road and Chelsea Embankment are also subject to a 20mph limit and TfL has announced plans to introduce 20mph limits on other parts of its network in Kensington and Chelsea.

The Experimental Traffic Order (ETO) making the 20mph limit took effect on 13 November 2020 and invited comments and representations on the new limit up to 1 October 2021. 

We reviewed all the comments we received and on 30 March 2022 the Director of Streets and Regulatory Services, confirmed that the Council would make the experimental borough-wide 20mph speed limit permanent as the best available option in terms of consistency, streetscape, cost, liveability and road safety. You can read the final Decision Report below:

Questions

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 until now there has been  very little evidence regarding the impacts of 20mph limits on the number of vehicles driving at high speeds (i.e. over 30mph).

As we introduced the experimental borough-wide scheme during the pandemic, we were not able to collect any robust ‘before’ speed data. It was widely observed that in addition to traffic volumes falling sharply at that time, there was an increase in the incidence of higher speeds across London.

We therefore used speed data at 27 locations from 15 streets within the scheme area collected between 2018 and February 2020, before the pandemic impacted traffic patterns, as our ‘before’ data. We collected ‘after’ data at these sites in early December 2021, when traffic patterns had returned to relatively normal, and before the Government’s announcement to move to ‘Plan B’ measures following the spread of the Omicron variant of Covid-19.

As with the pilot scheme, the monitoring results were very encouraging, showing average 85th percentile speed reductions at 23 of the 27 locations, with no change at one site and small increases at the remaining three. The reductions ranged between 0.6mph and 5.0mph. The number of vehicles travelling over 30mph decreased at 22 locations and increased at five. The reductions ranged between three per cent and 100 per cent with a decrease of more than 50 per cent at 14 of these 22 sites. 

How will we monitor the impacts of the scheme?

We will continue to monitor speeds across the borough and will prioritise those with the highest speeds, particularly those on cycle routes, for additional 20mph roundel markings, Speed Indicator Devices (SIDs) and ultimately traffic calming measures subject to available TfL / Borough funding and local consultation. We will also continue to consider applications for Neighbourhood Community Infrastructure Levy funded traffic calming, again subject to local support.

Does 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 vehicles 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. We have had very few reports of journey times increasing because of the lower limits.

Most studies do not account for how speeding restrictions may affect people’s choices around how they travel. We think lower speed limits 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 is  the new limit be enforced? Will there be speed cameras?

As with existing speed limits, 20mph limits can only be enforced by the police using on-street officers, mobile speed cameras and fixed speed cameras. TfL reports that in 2018, 154,785 people were caught and penalised for speeding related offences across London, including 38,878 on 20mph limit roads. Furthermore, there were 263,000 prosecutions for speeding offences in London during 2020 and 360,000 during 2021. Plans are also in place to give more than 500 Police Community Support Officers (PCSOs) in London speed enforcement powers.

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.

Does the Council benefit financially from this scheme?

The Council does not receive any revenue as a result of the scheme. As noted above, we have no powers to issue fines for speeding.

Last updated: 28 April 2022