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  • Writer's pictureMichal J A Paszkiewicz

London's 20mph roads

Anyone who has ever driven both in and outside London will know the huge difference in traffic and how much harder it is to get anywhere once you are inside of London. I recently moved out of London to Gloucestershire and I have noticed that given say an hour, you can drive numerous times further than you could in London.

Approaches to traffic in London have changed frequently in the past few decades and speed of travel is not a metric that is emphasized at the political level. It will still be a metric worked upon by transport planners looking at particular junctions or corridors leading into or out of the center, but larger political movements can more than counter these local improvements.

In 2003, London had the Congestion Charge introduced as a means to try to reduce traffic in central London and therefore improve traffic flow. This wasn't of course the only reason - the authorities were also keen on reducing air and noise pollution and raise further funds for improving the transport network. The London Congestion Charge zone is one of the biggest such zones in the world. Drivers entering the zone will pay £15 for entering on that day, irrespective of how much they travel.

By 2016, the Congestion Charge zone was no longer fulfilling its function in reducing traffic. The Evening Standard published an article claiming that traffic in London was so bad that buses were travelling slower than horse drawn carts had done a century earlier. The London Assembly published a document in 2017 entitled London Stalling, which looked at the issues causing traffic and concluded that it was largely due to private hire cab companies such as Uber and delivery vans. Both of these groups of drivers benefit from the fact they only pay the charge once and can then travel a lot in the zone over the rest of the day. The London Assembly proposed to introduce a different charge based on mileage rather than a single charge for a day.

Sadiq Khan, the Mayor of London, had other priorities than the London Assembly. He championed a policy called Vision Zero, which prioritised safety over traffic flow. The idea is based on the knowledge that chance of death or injury considerably decreases as vehicles move slower. By reducing the usual 30mph zones in London to have a limit of 20mph, the theory was that the amount of deaths due to road collisions should be reduced to Zero.

Has Vision Zero worked? There certainly haven't been any years where there have been no deaths on London's roads yet. On the other hand, Transport for London published a document in 2021 showing that deaths had decreased by 44% since 2005, and out of this, child deaths had decreased by 68%. This is no trivial change and can be considered a victory. But there remains a question as to whether this decrease was more affected by the decrease in speed limits than by the COVID-19 lockdowns that were still occurring in 2021, reducing the amount of people travelling.

Either way, the new 20mph limits are still a hot political topic, which can be seen by looking at a map of all the 20mph roads of London:

A map of just 20mph roads across London

Even before adding the divisions by Local Authority District, it is easy to see that there are clear boundaries where 20mph limits have been brought in and where they haven't. Once the divisions are added, it is easy to spot that districts such as Hillingdon, Barnet, Redbridge, Bromley and Elmbridge have had no interest in implementing these changes.

A map of 20mph roads across London split by Local Authority Districts

A few areas perhaps look like some local authorities have mixed feelings, but these white patches are easily filled with London's larger parks:

London's 20mph roads, Local Authority Districts and parks

Some areas are still perhaps not as clear-cut in implementing the Vision Zero policies such as in Sutton, but the fact that there is a political divide is pretty clear. Londoners will know however that the 20mph zones may be implemented in many of these areas, but are not enforced. Driving around Ealing at 20mph I noticed I was overtaken by many drivers who weren't breaching the 30mph limit that used to be there, but were adamant not to abide by the 20mph limit that would increase their travel time by 50%. I spotted both buses and police cars travelling along at 30mph. Those who know a bit of Transport History will recognise the similarity with the Motor Car act 1903 which also introduced a 20mph limit. This limit was abolished soon after by the Road Traffic Act 1930 due to the fact that it was widely disobeyed and therefore was considered unmaintainable. Is the same likely to happen to London?

Data from OpenStreetMap, available under the Open Database License.


Michal is a Software Developer with over a decade of experience, the majority of which he has worked on complex Transport systems. When he isn't working, he spends more time learning about Transport than is healthy for him.

If you learnt anything here, or enjoyed reading this analysis, please support Michal by buying his new book - The Perfect Transport: and the science of why you can't have it.

Some of his other writing and interactive content on Transport can also be found on his blog.

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