20mph speed limits

Increasingly it is accepted that 20mph speed limits save lives, and they are being implemented on residential roads across many London boroughs. Where cyclists must share space with motor traffic, reducing the speed differential is important: both for reducing the risk of death and injury, and for creating more pleasant cycling and walking environments. Yet many parts of London are still 30mph; although it's great to see boroughs adopting 20mph limits often it's only on 'residential roads', meaning that local high streets can still carry inappropriately fast traffic. 

 

The Problem 

 

The Transport Research Laboratory has stated: ‘It is well established that speed is a contributory factor in a large number of accidents.’ Speed significantly increases the chance of being injured in a collision. One of the first studies of pedestrian injury and car impact speed put the chances of being fatally injured at about 3% for a car speed of 20mph, as against about 20% at 30mph. In London, although rates have fallen, over 20% of all road deaths are still linked to excess speeds, with risks particularly high for young drivers. 

 

The Solution 

 

Reducing speed limits to 20mph in residential areas has been proven to reduce road danger significantly for all road users; in particular cyclists and pedestrians, and we would encourage it to be introduced on all non-motorway roads in Greater London. We support the enforcement of speed limits with cameras, including average speed cameras.

In 2008, a report to the London Road Safety Unit confirmed the findings of earlier work, that London’s 20 mph zones have had an effect on reducing casualties. Following this, we’re seeing 20mph limits implemented across many London boroughs, although often this is only on ‘residential roads’.

Where cyclists share space with motor traffic, reducing the speed differential can help both in reducing the risk of death and injury, and in creating more pleasant cycling and walking environments. However, many parts of London are still 30mph, meaning roads such as local high streets can still carry inappropriately fast motor traffic. Elsewhere, 20mph limits may not always be respected. 

 

There is a distinction between 20mph limits, and 20mph zones. 20mph limits are areas where the speed limit has been reduced to 20 mph but there are no physical measures to reduce vehicle speeds, only repeated signs to remind drivers of the speed limit. Guidance suggests this is most appropriate for roads where average speeds are already below 24mph, and for roads which give the impression that a 20mph speed or below is the most appropriate. 

 

20mph zones use traffic calming measures to slow vehicles down to 20mph and below, meaning that the zone should be ‘self-enforcing’. This can include speed humps, chicanes, road narrowing, trees or planters. It is important that such measures do not discourage cycling or put cyclists at risk. Badly designed chicanes can encourage close overtaking, while traditional speed humps can be uncomfortable and potentially hazardous. Better solutions exist: for example, high quality cycle bypasses around road narrowings and sinusoidal humps. 

 

What might this mean at ward level? 


  • A 20mph limit or zone across the local ward 
  • The extension of 20mph to a local high street 
  • Where 20mph exists locally, enforcement where needed 
  • Where needed, upgrading traffic calming measures so they discourage speeding motorists without causing problems for cyclists