In 30 years we’ve gone from a few local experiments, to 20mph now becoming the standard for residential streets in many places. But is this enough? New car technology means there’s now a growing case for 10mph limits, and they could help fill the gap where Low Traffic Neighbourhoods (LTNs) have been rejected.
I started my career in journalism, where I covered some of those early 20mph experiments. Each had to be signed off by the Secretary of State, and were only allowed where road design made them self-enforcing. As evidence mounted that they worked, rules were relaxed and 20mph zones spread. Now cities such as Manchester will soon by mostly 20mph, while Wales plans to make it the default across the country.
And 20mph works. A study last week by Transport for London found it had cut collisions and serious injuries by 25%. That’s great for inner-urban main roads, but there are plenty of smaller, narrow residential side-streets where sensible drivers would see 20mph as recklessly fast. So why do we still allow it?
Of course in many countries, lower speed limits are already common. In much of Europe 30kmph (18.6mph) limits are standard, while residential streets in parts of Belgium are now 20kmph (12.4mph) and in the Netherlands two million people live on 15kmph (9.3mph) “woonerf” streets.
These lower speeds make a big difference. At 20mph your stopping distance is about two and a half times further than at 10mph, and your kinetic energy (the punch you pack in a crash) is four times higher. The higher your speed, the further ahead you focus, making you less aware of your immediate surroundings. Faster vehicles are not only more likely to hit people, but the consequence of any crash are much more severe. In local residential side-streets with pedestrians, cyclists and children, 10mph could literally be a life saver.
But in the UK we only see 10mph limits on private roads as anything below 20 needs special permission from the government. One reason for the reluctance is compliance. In perhaps our greatest collective act of mass defiance of the law, average traffic speeds on 20mph roads are 30% above the speed limit according to the DfT. What’s the point of lowering limits if we’re all going to ignore them anyway?
Well that all changes now, thanks to mandatory speed limiters fitted to all new cars. Using cameras and GPS to check the speed limit, drivers are first warned, then the car is automatically slowed down. They can be overridden, but over time as the technology spreads through the car parc (the rather confusing term transport planners use for the stock of all cars in the country) we’ll see most traffic automatically complying with speed limits most of the time.
At that point we may be able to do away with speed humps. The public may even come to see speeding enforcement not as “sneaky” or “unfair” picking on ordinary drivers, but instead as justified punishment of the minority who have actively set out to break rules that the rest of us abide by. It also means 10mph speed limits would become self-enforcing and practical.
As well as reducing serious injuries, 10mph limits could bring other benefits. One response to rat-running through unsuitable residential streets has been to block them with traffic filters. But while these LTNs are generally very popular when well-established, it has proved politically difficult to introduce new ones in some places. In the meantime, lower speed limits could help make side streets unattractive to satnavs that are constantly seeking out the fastest route.
It also dramatically reduces conflict between drivers and cyclists. At 20mph, most cyclists are an obstacle to motorists, leading impatient drivers to force their way past dangerously. At 10mph, cyclists and drivers are mostly at a similar pace, and co-exist in a totally different way.
Would people accept 10mph? It’s clearly impractical for through routes, but for side streets designed just for living on, slower speeds would cause very little inconvenience. If the first and last couple of hundred metres of your journey were 10mph rather then 20mph, it would add just 45 seconds to your whole trip. And in return, you could get to live on a safe, quiet, street even without any barriers.
The technology to make speed limits work is finally here, 20 is more than plenty, it’s time we started planning for 10.
Barney's Blog 