20mph Speed Limits - A Collision of Compromises.

SmokingCaterpillar  December 15 2024 12:49:47 PM

There's a lot of often heated debate about the pros and cons of 20 mph speed limits in Wales and also selected parts of England - with the added context that I live on a road that is subject to a 20 mph limit. Also I have an A full motorcycle licence, own an electric motorcycle, a small car and a 3. 5 tonne motorhome.

I suppose the first question is 'what does a 20 mph speed limit result in?'

From my perspective. There are 2 main consequences of the 20 mph policy. There are others, but these two are the main ones I would like to focus on here.

• Reduction in the number and severity of road traffic accidents.
• Increased journey times.
   

Considering the first point, since its introduction in Wales. It's important to note that relevant data is only available for a relatively short period. It seems to be that the first 6 months of the scheme's operation coincided with a 29% reduction in casualties (considered to be deaths or serious injury. The data seems to be reliable, from the Welsh Government, the BBC, the Guardian and Insurance companies. Interestingly an insurance company, ESure, in a press release, reduced insurance premiums for drivers in Wales. Not all insurance companies have followed suit, though.

Now, I would be the first person to point out that correlation does not necessarily mean causation. But in this case, there seems to enough circumstantial evidence to come to the conclusion that there is a causal link and thus it seems to be a reasonable thing to conclude that the reduction in speed limit has had a positive effect on road accident stations. The level of that positive effect is much more difficult to quantify, though.

It's worth noting that adherence to the 20 mph limit is patchy. Some estimates state that overall traffic rates in 30 mph have dropped some 3-4 mph. This says to me that there is still some room for improvement- the main offenders are possibly people who don't observe the 30 mph limit, never mind a 20 mph limit. Better adherence may well improve the safety benefits of the policy.

Moving on to the second point. Does it actually affect traffic flow rates? If it does, then how significant is it?

The first thing to realise is that 20 mph limits are only within built up areas. If I am to drive from Birmingham to, say, Norwich, then most of my drivingis going to be subject to the national speed limit, and I would not expect there to be significant increases in journey time for this type of journey.

Instead, let's pick a good sized urban environment - say Birmingham. The average urban speed actually achieved is generally thought to be and 18 mph, with London at 9mph and Bristol around 13mph.

It's difficult to come up with an way in which we can calculate the changes in average speeds because of the sheer number of variables that can affect the final result. Intuitively, one would expect a reduction, but it is probably less than one would expect. In the same way that increasing speed limits doesn't necessarily translate directly into comparable traffic flow improvements.

So now, what offer does it have on driving times? I would argue that it is relatively small, though I concede that is very likely exists. And whether it matters is quite subjective, though there's a strong objective element as well. For example, haulage firms, where margins are slim, would objective face longer journey times - a major factor in costing models.

And so we come to the final choice. And here's a point that I think some people miss. We already, as a society accept many risks without understanding the ideas behind that risk. I'm guilty of making flippant remark to some vaccine deniers/hesitants, that if they were truly concerned about their or their loved ones' safety, they'd be making a significantly large reduction in the risk to the overall risk by not using cars. The risk of death or injury through driving is almost certainly higher that any routine NHS vaccine such as COVID or flu. Just for the record, I have had flu, pneumonia, shingles, COVID and RSV immunisations.

Anyway, back to 20 mph. This is a personal opinion, of course, but I find I'm willing to trade relatively small increases in journey time with a significant increase in injured and fatalities. At the same time, I accept that clearly we need to make progress on the roads (a point that was made to me when I was learning for my class A motorcycle licence). An interesting historical example - the first cars in the UK were subject to a 5 mph speed limit and had to have a man (this was some time ago) with a red flag walking in front of the vehicle.

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