20 mph zones?

[Tim Lund]

In the 'East London Line Extension - update on progress' thread, Pstaveley wrote:

If you run more trains and you do not increase the track capacity then you end up running slower trains.

It works with roads as well; if you want to get more cars along a road - safely - in a given period, you need to get them to slow down. When I read the Highway Code for my driving test - in 1979 - I noticed that braking distances increased in proportion to the square of speed, from which this follows with remorseless mathematical logic. So, where roads are up against capacity, as they are inevitably in cities, traffic has to go slower. It also means fewer people get killed and seriously injured.

The 'slow down to make roads more efficient' argument may not seem to justify slower speed limits, because most drivers are sensible enough to adjust their speed to the traffic density without being coerced. But it does suggest that if slower speed limits were introduced, responsible drivers would be able to get over it, and also that they would hardly undermine the local economy.

The problem is where the reasons to slow down are not so obvious to normally responsible drivers - e.g. residential and side roads where it would be great if people walking to shops and other local amenities were not put off by cars going uncomfortably fast. I know there are serious issues with enforcement - why else would road humps have ever been introduced? - but there are 20 mph zones in other parts of London.

Would other STFers like to see them here?

[chrisj1948]

I am in favour of it. The consolidated report about 20-mph zones published recently was positive about the benefits in terms of reduced deaths and serious injuries to pedestrians and cyclists, and the zones do improve the quality of life for those living within them. There has been an argument, promoted by the AA, that there would be negative environmental effects because a typical car uses more fuel driving at 20mph in third gear than 30mph in fourth, but this applies only to steady speed conditions, which are unlikely in a residential urban area.

Enforcement seems to be the main perceived problem. Humps are expensive and are disliked both by motorists and residents. Signage is costly and unsightly. I would favour a system similar to that used when the 30mph limit was introduced in the 1930's, when the presence of street lamps less than 200 yards apart indicated a restricted zone. Within an existing 30 zone the absence of central road markings could indicate, in the absence of signage to the contrary, that this was a 20 zone.

Some argue that in the absence of active enforcement the new limits would just be ignored. They would, by some motorists, but the average speed would still drop. Average speed detection systems which are far less costly and obtrusive than the current SPECS cameras we are familiar with at motorway road works are being developed, and these could provide a means of enforcement in the long term.

The average speed of a vehicle through an urban environment is significantly less than 20mph as it is. Residential 20 zones would not significantly increase journey times. More importantly, they would help return residential streets to the people who live in them. Walking and cycling would be more pleasant, noise levels would be reduced, and the fear of traffic which causes many parents to keep their children indoors would be reduced.

Regards
Chris

[stuart]

Chris - the point was the study showed that existing London 20 mph zones were indeed effective at reducing deaths and injury. However it was implicit in the report that the humps etc had reduced average road speeds by about 10mph from 27mph to 17mph.

It gives no substance to 20 mph zones being effective without this passive enforcement. So its the humps that reduce death - not the signs.

It would be great if we could reduce speed and accidents without the discomfort and cost of humps. However the police have largely withdrawn from traffic law enforcement and would be even more expensive. History shows that too large a proportion of drivers are prepared not to attempt to drive safely or obey safety laws without enforcement a great deal tougher than we have today.

The real answer is to get a mind shift amongst those drivers. But how to change car culture? Till somebody comes up with a proven idea we have the choice of a mess in the street or a bloody mess in the street.

I hate humps but see no alternative ...

Stuart

[leenewham]

I hate bumps too...I lived in a 20mph zone and no-one ever observed it to it.

Mind you, no-one observed much to do with law there, whether it be smoking or dealing in drugs, shooting people or throwing them through windows!

This was all reported to the police (who weren't bothered) and is in the past in case admin has a problem with it!

[chrisj1948]

Stuart - I regret to say that I have, by and large, to agree with you. A speed limit by itself does not enforce 100% compliance, but aggressive humps do a pretty good job.

Nevertheless I would be in favour of introducing residential 20mph zones even without traffic calming measures. A significant proportion of drivers would comply with them, which would be an improvement, and if they were widespread, rather than the current exceptions, you might gradually get a change in mindset. Again, if they are widespread, occasional speed traps begin to have a deterrent effect beyond their number because the fear of them extends to the whole 20mph system.

As a pessimistic argument I would say that introduction of the zones, even without aggressive enforcement, would still be an improvement on the current situation.

Regards
Chris

[marymck]

No to 20mph zones and no to speed humps.
Yes to more education: of motor vehicle drivers, of pedestrians and of cyclists.

I live on a hill, which has a 30 mph speed limit. This speed limit is continually broken by motorists. A few years ago I tried to get a speed camera set up in the road. The Council refused to consider this until there had been four fatalities or serious injuries (I think within a given time limit, but I can't remember what that was).

Humps are out of the question. Firstly, the cars won't be going slowly enough and the bumps will cause injuries and damage. Secondly, the road surface is already extremely noisy and humps would make it impossible to sleep at night. And a sleep deprived driver (or pedestrian or cyclist) is a dangerous beast.

I have also been driving along roads with speed humps where cyclists have suddenly veered in front of my car because they're trying to avoid humps.

There's also a serious issue with some of the speed humps we already have in this area. They're higher than the legal maximum!

I'm also strongly against 20mph zones in all but VERY built up areas, because they're frankly so difficult to drive on. Unless the prevailing road conditions are such that driving at less than 20mph is natural, then one is constantly being distracted by the speedometer and not looking at the road.

I have also been driving at far less than 20mph when I have been overtaken (on the inside!) by a cyclist! So I really do think the rules of the road need to apply to all road users.

Which brings me onto my next point ...

When I was at school we were given cycling proficiency tests. We were also taught how to cross the road safely AND to "wear something bright in the night" AND to actually stop at zebra crossings and not to sidle up to them and step out regardless of whether a vehicle is too close to safely stop.

[stuart]

Mary,

I sympathise with your feelings. I shared them too - once. However one should not allow one's personal experience to over rule compelling evidence. And there is compelling evidence here: http://www.bmj.com/cgi/content/full/339/dec10_3/b4469

The introduction of 20 mph zones was associated with a 41.9% (95% confidence interval 36.0% to 47.8%) reduction in road casualties, after adjustment for underlying time trends. The percentage reduction was greatest in younger children and greater for the category of killed or seriously injured casualties than for minor injuries.

Read that again, slowly. The implications are stunning. So stunning that much work is needed to refine the conclusions and consider how they could or should be implemented.

To ignore it is condemning people to death and mutilation. Could you live with that? The issue is that cars kill. Sometimes it is the driver's fault, sometimes it is somebody else's. You will note that children benefit proportionately more than adults. Probably because they ran out into the road and are at fault. But at 20 mph the driver has more time to spot and take evasive action. Any impact is going to be a magnitude less. And even an innocent driver with blood on his bonnet is a victim for life.

We have something that does work - 20 mph zones. If you can show something that works better - fine, we all want just that. But meanwhile why should we not start doing 20 mph zones in the areas that might benefit most?

Stuart

[dickp]

Alternatively, idiotic pedestrians and inattentive parents could always look where they are going before walking out in front of cars? That would probably help reduce accidents quite a bit.

It would certainly make driving along Sydenham High Street a hell of a lot less stressful.

Just a thought.

[stuart]

Alternatively, idiotic pedestrians and inattentive parents could always look where they are going before walking out in front of cars? That would probably help reduce accidents quite a bit.

Indeed they should keep off pavements too as rather too many are killed by idiotic and inattentive drivers who can't even keep the car on the road.

An idiot is an idiot but better blundering around on foot than on four wheels ... just another thought!

Stuart

[poppy]

Narrow residential streets would absolutely benefit from 20mph zones.

30mph-plus along streets with blind corners and hidden junctions is actually too fast. Dangerous and noisy!

I recently drove along a road with very low speed humps. They were very visible, red and textured in some way but barely raised off the ground. Even though in theory you could have driven over these very quickly, the markings seemed to have a psychological effect. They made me slow down, because I was not sure what to expect.

You will always get idiots who will break rules, and maybe eventually happily speed across humps like the ones I mentioned above, but I think this sort of approach would have an impact on most people.

[alywin]

Well, I live in the middle of a 20 mph zone. It contains some totally useless "traffic-calming" measures and some potentially highly dangerous ones. And I've never registered that anyone actually obeys the 20 mph limit, which makes the whole thing pretty pointless. Not to mention that I've sat in cabs with the driver weaving along the road so he can meet the road humps at the places where they do least damage to his car/impede his progress least. None of this will work unless drivers are educated properly to understand the dangers better (and actually drive better - I wonder sometimes how some of these people managed to pass their tests).

Plus, it's a decade or more since I've driven, and things may have changed, but I remember being told that 4th gear was the most efficient and 28 mph about the best speed for town driving. Unless car design has changed so markedly that cars can now do 20 mph in 4th, then the drivers will have to drop into 3rd and produce more pollution. There will presumably then be a corresponding increase in health problems and deaths caused by that which will to some extent offset the gains made, although I don't suppose that will be registered.

[Robin Orton]

Nobody on this thread seems to have mentioned the possibility of encouraging speed limit compliance by installing the indicative warning signs that flash at you when you're exceeding the limit. I always slow down when I activate one of these, although I recognize that not everyone might. Much more user-friendly than speed humps, I'd have thought. But perhaps they fall within chrisj1948's category of 'costly and unsightly signage'?