The Non-story of 20mph Enforcement In London

A few weeks ago, Times consumer affairs correspondent Andrew Ellson authored an article on 20mph speed enforcement in which he took some umbrage at how London's Metropolitan Police deals with enforcing that particular speed limit.

I'll come to what he wrote in a minute, but this comes at a time when we've had all sorts of nonsense from people decrying any measure to rein in the impact of decades of traffic growth and indeed, enforcement action taken against those behaving dangerously.

I am a supporter of 20mph as the default speed limit. This doesn't come from a political position, it is a consequence of the science which underlies part of the sustainable safety (also called safe systems) approach to highway engineering. In short, the human body can withstand certain forces in terms of being hit by a vehicle or for the occupants of a vehicle, and the relationship between driver speed and the energy of an impact is non-linear. 

20mph (30kph) is the sweet spot for where people both inside and outside of vehicles are much more likely to walk away from a crash and so from a sustainable safety point of view, places where mixed modes operate will benefit from this speed limit. I wrote more about this back in 2020. Let us also be very clear here, 20mph is a limit and not a target, because in some situations it is fully appropriate for people to drive well below the limit because of what is going on around them.

I think that in some respects UK driving culture has got us to a point where some people think about the speed limit as a bit of a guideline and with well-publicised police enforcement approaches, many people realise they are very unlikely to be taken to task for being a little over the limit and in the event they do get caught, some people get very noisily upset and that's grabbed by some to stoke their silly little culture war and presumably it must also help sell newspapers or drive traffic to news websites.

So back to Ellson's piece. While he did mention police forces across the UK, I am going to stick with the Metropolitan police as he seems most upset with them.  The headline to his piece (that he won't have written) leans into the government's current culture war on anyone not driving with "Record fines for 20mph speeding despite PM’s pledge to scrap zones" and in the piece after talking about 20mph, Ellson states:

"The Met alone has issued 595,000 of the fines — the equivalent of one ticket for every four cars registered in London — amid a crackdown on speeding initiated by Sadiq Khan as mayor."

In June 2023, there were 2,608,538 cars registered in London and with Ellson's figure of 595k fines, that's a ratio of 4.38. Now according to the data provided to me by the Met around 20mph enforcement, there were 243,110 offences detected by camera and 2,637 Traffic Offence Reports (TORs) - i.e. detected by a police officer in 2023. That's a total of 245,747 which is a ratio of 10.6. In fairness, the data I have is all offences and not just cars, but it doesn't appear to be the 1 in 4 as suggested in the article.

Ellson then took to Twitter to talk more about this and we find out that just maybe, he was feeling a little sore about the subject and so I obviously couldn't resist a dig. His answer was interesting and I did ask to see his data, but reply there came none.

The 10% +2mph here refers to a commonly held belief by some drivers that they are fine to drive at that speed before they run the risk of enforcement. For 20mph, this is taken as 24mph is fine, enforcement will be from 25mph and greater. Except that's completely wrong because the Met confirmed its 20mph approach in November 2021 as follows;

"The Met threshold for enforcement of 20mph roads and issuing a speeding ticket is 10% + 2 mph. Enforcement from 24 mph and Prosecution from 35 mph."

So if they catch you driving 24mph to 34mph (officer or camera) you are more likely to be dealt with through the fixed penalty process or a speed awareness course, and from and including 35mph, that's probably you off to court.

Ellson's tweet is even more interesting because he is talking about between 21mph and 25mph. He didn't confirm if that was an inclusive figure, but anyone caught speeding at 24mph and 25mph will be subject to enforcement. But let's have a look a the actual data which shows that in 2023 from a speed camera perspective, not a single person was subject to enforcement in London for 21mph to 23mph inclusive which is in line with the 10% +2mph which starts at 24mph. 

For enforcement by an officer for 21mph to 23mph, one person was subject to enforcement and that was dealt with by a speed awareness course. There were no enforcements by an officer at 24mph and there were just four at 25mph (1 case ongoing, 2 for potential prosecution and 1 dealt with by a speed awareness course). Back with the cameras, there were 80,267 enforcement detections at 24mph and 56,764 at 25mph.

Ellson is being a bit naughty quoting the range of 21mph to 25mph because that's taking in 21, 22 and 23mph which objectively is not being enforced against, but it's good framing when you want to create criticism even though we still talking about a 20mph limit and it feeds the social media set-piece of unverifiable stories about old ladies being done for driving at 22mph in a 20mph limit.

But let us put this into perspective with the Met's total 20mph enforcement figure of 245,747. About 42% of camera detections ended up with a speed awareness course and about 13% when detected by an officer, but as officer detections are about 1% of the total, you've got to be quite "unlucky". About 17% of camera detections led to people paying their fines (and taking 3 points), less than 4% going for prosecution, about 29% remain ongoing cases and about 9% led to no further action.

In terms of mileage driven in London, in 2022, there were 19.1 billion miles driven. I don't have a breakdown of how many were on 20mph streets, but that's one 20mph enforcement detection for every 78,000 miles driven in London each year and I'd say we've actually got some good compliance out there which makes Ellson's whole story rather disproportionate in the grand scheme of things. And besides, physics and biomechanics don't care.

I've provided the Met data below, feel free to challenge by maths as I don't always get it right!