The Great 20mph con.

You may have noticed the gradual move in recent months to blanket 20mph limits by default in residential areas. These seek to replace the 30mph zones that have typically been in place since March 1935. Many, though not all boroughs of London have introduced them and in July 2022 the Welsh Parliament indicated that the default speed for built up/residential areas would move from 30mph to 20mph within 18 months.

Firstly declared interests. I'm a life long driver and I live in part of rural Wiltshire where public transport is woefully inadequate and you couldn't use it to commute to work or have any form of social life as it stops around 5pm. So there are some places where a car is pretty much a necessity. I've also been a cyclist since the age of around nine and enjoy both urban and rural cycling now.

I don't believe cars are bad bikes are good and I do believe in stopping for red lights when cycling and in driving in a courteous manner to cyclists when I'm driving. Strangely enough, I'm also a pedestrian at time in Wiltshire and in central London. I don't believe in a hierarchy of road users, and am idealistic enough to believe the rules apply to all and all should be able to coexist and treat other road users with respect.

As to twenty mile speed limits, I'm unconvinced they do anything effective in reducing speed, but I'm in good company, the most recent Ministry of Transport report in 2018 found exactly the same thing. There may be areas where 20mph is appropriate based on the data or proximity to a school etc, but I do not support blanket default limits being reduced to 20mph.

You can do anything if it makes us (feel) safer

Some in my readership may have heard of a long lost art recommended from time to time on this site. That art is critical thought supported by reference to a sound evidence base. I would encourage such an approach when examining this subject.

So, why this sudden move to slow the default speed limits.

There are usually three strands given as primary reasons for such a change. These are safety (nearly always the primary reason). The argument being speed kills and every mile slower reduces the risk of fatalities. These safety concerns are usually focused on child safety. The second is the increase in living standard (utility) of those living in residential areas with the third being an increase to general health by reducing emissions. Some (but not many) admit to secondary or tertiary objectives of moving people from cars to cycles and walking by inconveniencing them off the roads. So let's look at some of those claims.

Just before we do, I bring a subtly different but related matter to your attention, one that has been rattling around since at least the 18th century.

Benjamin Franklin highlighted the trade off between liberty and freedom in the late 1700's a subject returned to by those as varied as Barack Obama, Hitler, George W. Bush, Donald Trump, Theresa May, old uncle Tom Cobley and all.

It is not my position that the freedom to drive at 30mph is an essential liberty (such as freedom of speech, association, religious belief etc) but it is a restriction on a current freedom being defended on the basis of safety. It also shows that using 'safety' as a justification for restricting or limiting activity has been a well trodden path for centuries. That's probably because it works as a claim - who wouldn't want to be safer?

I'm highly qualified don't you know

The question is do these limits make you safer and achieve their stated aims? Who might be able to help us with that one? Enter stage left Transport planners. You know, the highly qualified,. mostly urban insular bunch of experts who tell us they know best. While I have nothing against planners on a personal basis, as a professional cohort they are singularly elitist and aloof shunning scrutiny even more than notable politicians.

I must point out these are the same experts that brough us 'safer motorways' meaning no hard shoulder, no emergency reserve and turned out neither to reduce emissions, smooth traffic or increase safety but cost us billions.

These were the highly qualified professionals who have combined efforts and made sure we have a truly world class highly integrated and customer focused planned infrastructure over the last half a century. They also champion cycle lanes that run out leaving you surrounded in traffic or dump the rush hour cycling flood onto the pavements. - Surprisingly, they remain very quiet when challenged about the efficacy of their creations - I wonder why that may be? The last two I asked told me (in terms) they couldn't be arsed their credentials speak for themselves I don't deal with data I don't like. Little help there then. So what might that data include?

1. Reducing from 30mph to 20mph will reduce fatalities as an impact at 30mph is far more destructive than at 20mph.

As an argument this is seems quite sensible, but a couple of points before we rush headlong into the millions of pounds cost in resigning, new road marking and necessary enforcement. The first question is proportionality - how big is the problem we're trying to solve? Just how many fatalities or serious injuries are there on the UK roads in 30mph zones?

Source: National statistics Reported road casualties Great Britain, annual report: 2020

Firstly, the UK is doing a pretty reasonable job at improving road safety without the need for blanket reductions of this type.

Of course, this only shows trends, but it certainly suggests we don't have increasing carnage on our roads. So can we get a view on some actual numbers around these trends. Perhaps we can then see if the disruption is addressing a real or perceived issue and whether it's the best way to spend a not insignificant chunk of change that might be better spent elsewhere.

Source: National statistics Reported road casualties Great Britain, annual report: 2020

You may be surprised to see the actual figures surrounding child fatalities and indeed all road collision casualties.

In 2019/20, 52 fatalities involved children (under 17). That includes all motorway, dual carriageway and 50mph zones. When you look at police reporting figures there are around 20 UK fatalities in zones where 30mph was in place. In over 85% of cases where there was serious injury or above they took place at higher speeds..

What is interesting is the counter intuitive impact of moving to a 20mph zone you've declared safer. People behave as if it is safer whether or not that is actually the case

Research carried out for the Department of Transport (see did not provide statistically significant evidence that wide area 20mph limits reduce vulnerable road user casualties. Joint ABD/ Bridgstock evidence presented to the Scottish Rural, Economic and Connectivity (REC) Committee in February 2019 provided documented evidence of increases in vulnerable road user deaths and serious injuries after the implementation of some 20mph zones, which had replaced previously 30mph ones (

Then there are the assumptions in the claim about impact damage. It is true that an object moving at higher speed would have a greater impact. The question is what proportion of the accidents in 30mph zones have that 10mph difference that helps justify the claims made for 20mph zones?

This was studies by the Department of Transport (Publication No.16 – Relationship between Speed and Risk of Fatal Injury: Pedestrians and Car Occupants, TRL, Sep 2010) Around 2% of UK urban adult-, and 0.6% of urban child-, pedestrian casualties are fatalities. The Ashton and Mackay curve tells us that for this to the case, the average impact speed in 30mph zones is already below 20mph

Source: Publication No.16 – Relationship between Speed and Risk of Fatal Injury: Pedestrians and Car Occupants, TRL, Sep 2010

2. 20mph zones increase the social amenity (societal good) and generally increase the welfare of those living within them.

An interesting assertion, but as yet nobody seems able to present any studies that support that suggestion. This claim seems to be based on an ideological belief that a slow zone is a good thing and consequential belief that everyone would support that.

Evidence from those who have lived with the Transport planners wheeze report a less universally favourable outcome. Residents in Croydon are increasingly opposed to zones that have caused log jam through the centre of the town. In line with the Scottish examples cited earlier, a false reassurance means people pay less attention rather than more attention to road vehicles resulting in increases (in some cases) of distracted motorists, cyclists and pedestrians.

Indeed, in recent figures the top cause for collisions (Source: Police/Highways Agency accident reporting statistics) in urban environments is increasingly being recorded as distracted or inattentive participants. That may be a car driver, but it could equally be a pedestial texting while walking into the road, a cycle or moped crossing the central road marking or jumping lights etc. I'm not sure those involved in those increased incidents would consider their utility had been enhanced.

Monmouthshire has recently reversed one 20mph stretch and is considering further zones as they have increased congestion, raised incidents of road rage and made emergency vehicle responses significantly more difficult, all wonderful examples of an improved quality of life.

Both AA and RAC have raised concerns with government about the increased distraction placed on drivers in 20mph zones. Cruise controls typically require 25mph plus. When driving on the limit of lower gears in zones maintaining 20mhp with only a 2mph tolerance there is greater attention paid to gear changes and speedometer than would otherwise be focused on the road. Driver stress and incidents of road rage have increased so not everyone's utility is supercharged.

Source: Transport for London Emissions Studies

The we turn to emissions, surely a better story there? Well, not if you read Transport For London's own report (available at

Here is an example of the emissions curves for vehicles at varying speeds.

Most vehicles cannot maintain 20mph in anything above second gear which is far less efficient in terms of gearing and produces far higher levels of emissions. As if more log-jams, higher emissions, slower and more congested emergency response times and the potential to increase vulnerable road user collisions wasn't enough, consider trade.

The best example is the recent reduction of blanket speed reductions in parts of France. Here similar steps were taken reducing speeds and increasing travel time by around 50%.

Remember those road and planning experts, well France has them too. However, they've changed their minds on 90kmh - 80kmh blanket speed reductions as contrary to their suggestions there was no drop in accident or injury rates. What there was (due to increased delays, delivery issues, gridlock and travel cost increases) was a €4.4 billion reduction in the French rural economy. Not sure about you but the case for greater utility doesn't look overpoweringly strong to me.

So who is pushing for these changes (other than transport planners)?

A number of interest groups who have access to the same data still push for blanket 20mph zones, Some groups believe the whole of central London should be pedestrianised with one extending that wish to the whole of Greater London. However those are at the extreme edges of the pedestrianisation and environmental lobby.

One campaign group for shorthand the militant cycling wing of the road user community push for blanket 20mph as it appears they see all motor vehicles as the problem. There are also a significant number of high profile supporters.

Let me introduce you to Mr Jeremy Vine, a well known journalist and broadcaster and one of his recent social media post.

I caveat this with some reassurance that I'm not picking on Mr Vine in particular, but he is a person in a position of power and is one of a number of fairly extreme cyclists vocal in this space.

The video on the tweet has been inserted immediately below so you can make up your own mind.

For me there are a couple of telling points that are reflective of the wider movement who would have all cars removed from the road in favour of walking and cycling - easy enough if you live in central London with excellent publish transport and have a six figure salary for taxis as required. The same may not be true for everyone not in that position.

It is not my intention to set cyclist against driver, but it is my hope that both can coexist on limited road space along with pedestrians. That requires an ability to be objective and to consider the problems we ourselves present and how we could improve the situation.

In the video above (from Mr. Vine's tweet), this cyclist and the cyclist filming the incident ride down a crowded road and in a controlled crossing cross the main road marking towards an oncoming vehicle attempting a wheelie. Being unsuccessful the rider cycles into the car and is thrown off his bike and into the road and the pedestrian crossing.

Mr Vine's view appears to be that this isn't the problem - nothing to see here move right along. The issue would be if he got in a van then he'd be bound to kill five people. Others on the thread criticise the driver for not breaking or getting out of the cyclists way - give him more room for his stunt.

Mr Vine further justifies (or at least fails to criticise the act) by saying it doesn't really matter as it's only the cyclist at risk of harm unlike if a car hit him.

I leave you to form your own view as to whether the cyclist is the only person who may be harmed. I would suggest the driver concerned would have been pretty alarmed and had the accident been fatal or caused serious injury may have been significantly traumatised by events. Equally, a little less traction, an unluckier form, a busier road or crossing and pedestrians would have been at risk as would any other road users.

The relevance of this social media detour? Well, the militant cycling arm are one of the strongest voices demanding blanket speed restrictions. However, a significant minority are entirely unable to criticise anyone on two wheels or following the same rules of the road as everyone else is expected to be bound by.

If we are being asked to make vehicles travel at 20mph so stunts like this aren't dangerous for the cyclist or so those walking absent-mindedly or distractedly into the flow of traffic, then Houston, we have a problem.

What is the cost of this suggested change?

I hate to be vulgar and to bring up the cost of filthy luker, but exactly how much are we talking about to make these changes.

  • It may come as a surprise that local authorities are rather coy about answering that question. We do have some that have published estimates though. One of the 32 boroughs of London (Richmond on Thames) estimate that signage replacement and repainting would cost £700,000 in their borough. The Isle of Wight, one of the smallest proposed implementations comes in at just over £500,000 Bradford council cost one of their villages (Saltaire) at 750,000 so this isn't cheap. Wales has set aside £33 million for road signage changes but has not included anciliary costs such as consequential legislative change. An indicative figure for Scotland is in the low billions (£3.2) so this is a multi-billion pound expenditure being proposed. At this point, I refer the class to the findings of the Department of Transport in their 20mph Research report. (This can be found in full at This found:

  • 20mph zones have no meaningful impact on speed reduction, resulting in an average speed reduction of between 0.5 and 0.8 miles per hour.

  • There was no statistically relevant reduction in casualties or accident rates during their associated case studies

  • Built environment changes (chicanes. road narrowing and the like) are far more effective at speed reduction

  • There have been no significant changes in cycling uptake since the 20mph zones. There continues to be a range of barriers which discourage walking and cycling. time constraints and journey distance being the most common.

  • Without effective enforcement the zoning is largely ineffective. The report notes the resource constraints on Highways Agency and Roads Policing and found this was unable to fill the necessary enforcement role.

So, if at a time when money is tight you want somewhere in the order of £10-15 billion spent on a measure that is ineffective when measured against its stated aims roll right up. I for one would rather it was spent on more deserving policies that actually produce results.

So next time you hear how 20mph zones make you safer, reduce speed and improve the environment for the world as a whole - apply some critical thought. The available evidence says they are wrong.


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