TAPAS.network | 20 March 2023 | Commentary | Barney Stringer

Twenty’s Plenty – now Time for Ten?

Barney Stringer

Setting appropriate speed limits to meet both road safety and wider environmental and place quality objectives has become much more sophisticated and precise in recent years. At a neighbourhood level 20mph has increasingly been seen as the benchmark. But should we now be harnessing technology and site-specific assessment to bring in 10mph in some circumstances asks Barney Stringer.

AS FAR BACK as 1865 the law has prescribed different speed limits for different roads, with the so-called ‘Red Flag Act’ setting a national limit of 4mph, but just 2mph in built-up areas. These limits soon went higher, and there have been many adjustments since to reflect different types of roads and vehicles. Alongside this came measures to control the relevant driver behaviour on both safety, environmental and placemaking grounds.

Urban and suburban areas have had particular attention in recent decades, and in the last 30 years or so we’ve gone from a few local experiments with 20mph limits, to it becoming the standard limit for residential streets in many places. But is this enough? I would contend that new car technology means there’s now a growing case for the deployment of 10mph limits, and they could help fill the gap where Low Traffic Neighbourhoods (LTNs), and associated restricted access measures, have been locally rejected.

We’ve already come a long way. Those early 20mph experiments had to be individually signed off by the Secretary of State, and were only allowed where road design made them self-enforcing. As evidence mounted that they worked, implementation rules were relaxed and 20mph zones spread. Now councils as diverse as Manchester and Cornwall (LTT 861) plan to make most residential streets 20mph, while Wales is going further by making it the default across the country (LTT 860).

And 20mph works. A recent study by Transport for London found it had cut collisions and serious injuries by 25% (LTT 863). That’s a suitable speed for inner-urban main roads, but there are plenty of smaller, narrow residential side-streets where responsible 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 – 30kmph (18.6mph) is widespread in Europe and Asia, 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 consequences of any crash are much more severe. In local residential side-streets with pedestrians, cyclists and children, 10mph could literally be a life saver.

So far, in the UK, the only 10mph limits we see are on private roads, because anything below 20 needs special permission from the government. One reason for the reluctance is compliance. In perhaps one of the greatest collective acts of mass defiance of the law, the average speed of cars on 20mph roads is 30% above the speed limit according to the DfT. What’s the point of lowering limits if everyone’s going to ignore them anyway?
Well, addressing that issue all changes now, thanks to the 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 for the stock of all cars in the country!) we should start to see most traffic automatically complying with speed limits most of the time.

It will take until the 2030s before most cars on the road have speed limiters, but at that point, attitudes to speed could change significantly. As long as speeding remains something almost all drivers do to some degree, enforcement is too often seen as a “sneaky” or “unfair” intention of picking on ordinary drivers, or even just as a backdoor tax to raise money. A common reaction to a speeding ticket is to feel unlucky, rather than irresponsible. If, in future, speed limiters mean most vehicles don’t speed, then we may eventually come to see enforcement as proper punishment of the minority who have actively set out to break safety rules that the rest abide by.

Insurers are likely to play an increasing indirect role in enforcement too. Some already offer cheaper insurance to those with a black-box recorder to prove they drive safely. These recorders are now in all new cars, and for those involved in a collision, it will be clear if they had de-activated the limiter and were speeding. Cheaper insurance for obeying speed limits could in due course be a more palatable incentive than fines for breaking limits.

The potential for “mass defiance” of speed limits being replaced by “mass compliance” will have significant implications for road design. Drivers pick up cues from a road’s design speed even where it contradicts the specific speed limit imposed or what is actually safe. Wide empty lanes, long straight sightlines, sweeping curves, central hatching – all shout “this is a fast road”, drowning out the sign that says “20mph, school crossing”. With compliance so poor, and enforcement so difficult, physical changes to roads have been the most effective way to actually reduce speeds. We fill residential streets with chicanes, narrow gates, speed cushions and humps to tell drivers to go slow – might we be able to do away with all these if car technology means traffic sticks to the speed limit anyway?

But what about the locations where even those 20mph speed limits are not safe? Could it be reduced to 15mph or even 10mph in places, if speed limiters make it self-enforcing? Such slow speeds are unlikely ever to be appropriate on arterial or distributor roads – the through roads that take traffic that is going any distance. But what about on roads intended purely as somewhere to live, short residential side-streets that exist purely for access – the “inside” of a neighbourhood, rather than the boundary roads?

In the right locations, 10mph streets could bring many benefits beyond the obvious improvement in safety. Firstly the limit changes how we can design roads, not just removing the anti-speeding paraphernalia of humps and chicanes, but slower speeds mean we can narrow crossing widths at side turnings or create fully continuous pavements for pedestrians. It makes it easier to introduce pocket parks, playstreets, wider pavements, reduced street clutter and increased street planting. It improves the environment and attractiveness of a street – slower traffic is quieter and less polluting (both for local air quality and climate change), particularly in stop-start urban conditions.

A lower limit also changes how we use roads. It makes walking and cycling more attractive, partly because of safety, partly convenience as it’s easier to cross slower streets, but also because for short journeys walking can become quicker than driving and hunting for a parking space. And it dramatically reduces conflict between drivers and cyclists. Driving at 20mph, most cyclists are a slow obstacle to motorists, leading impatient drivers to take risks forcing their way past. At 10mph, cyclists and drivers are mostly at a similar pace, and co-exist in a totally different way without that dangerous speed differential.

A reduced limit also helps tackle the “satnav problem”. The hierarchy of arterial roads, distributor roads, and local streets is breaking down now that apps like Waze give drivers the ability to treat any part of the network as a shortcut. Streets built as somewhere to live are now co-opted as ‘mini bypasses’ or relief roads by non-locals. We’ve always tackled this rat-running with selective no-entries, banned turns and one-way streets. When well-established these “protections” from traffic are usually very popular with residents. But recently more concerted efforts to introduce LTNs have become politicised, even spawning bizarre conspiracy theories about people being purposely locked into areas to control them.

We should not give up on LTNs, but where highway engineering solutions have proved impossible, slower speed limits enforced in the way I’ve described could help fill part of the gap. Satnavs that are constantly seeking out the fastest route will be less likely to pick 10mph residential backstreets as a time-saving shortcut, which would help keep through traffic on through roads. And even for residents of those back streets it is a soft incentive to drive the shortest route in and out to the nearest distributor road, rather than threading through to the far side of the neighbourhood. So 10mph zones could not only slow traffic, but actually reduce it, even in places that have rejected LTNs.

Would people accept a 10mph limit? This very much depends on it being deployed on suitable roads, where it is obvious that slower speeds are appropriate and beneficial. That is likely to mean only in small residential zones, so you are never far from joining the network of faster roads. Crucially that means people would mainly experience 10mph as a resident on the street, rather than as a driver, which could be key to acceptance. If just the first and last couple of hundred metres of a journey were 10mph rather than 20mph, it would add only 45 seconds to the whole trip. For many people that would be a worthwhile trade for living on a safe, quiet, street, without needing any barriers.

The technology to make speed limits work is finally here - freeing us to think in more detail about what speeds are right where, not just what is enforceable. Twenty is more than plenty in some circumstances, so it’s time to start planning for ten.

Barney Stringer is a director at Quod, an independent consultancy at the cutting edge of planning, development economics, socio-economics and environmental planning, based in London and Leeds. He started his career at Local Transport Today, where he was assistant editor and twice winner of Transport Journalist of the Year.

This article was first published in LTT magazine, LTT865, 20 March 2023.

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Twenty’s Plenty – now Time for Ten?
Setting appropriate speed limits to meet both road safety and wider environmental and place quality objectives has become much more sophisticated and precise in recent years. At a neighbourhood level 20mph has increasingly been seen as the benchmark. But should we now be harnessing technology and site-specific assessment to bring in 10mph in some circumstances asks Barney Stringer.
Twenty’s Plenty – now Time for Ten?
Setting appropriate speed limits to meet both road safety and wider environmental and place quality objectives has become much more sophisticated and precise in recent years. At a neighbourhood level 20mph has increasingly been seen as the benchmark. But should we now be harnessing technology and site-specific assessment to bring in 10mph in some circumstances asks Barney Stringer.
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