Speed limits?

[Dan B]

There is a potential personal dilema as highlighted by the safe-speed website. The speed at which the lowest crash risk is approx at the 85 percentile.

Given safe(sic)speed's usual ability with figures, I am willing to bet this is a confusion between correlation and causation.

And what anyway is the 85th percentile speed in a typical urban 30? The cars may be moving at 25-30, the bikes at 12, the pedestrians at 4 and the street furniture at 0: any and all of these are entitled to be on the road and are potentially hazards that the driver must respond to. So "going at the same speed as everyone else" is a meaningless concept

 

[jonesy]

Given safe(sic)speed's usual ability with figures, I am willing to bet this is a confusion between correlation and causation.

And what anyway is the 85th percentile speed in a typical urban 30? The cars may be moving at 25-30, the bikes at 12, the pedestrians at 4 and the street furniture at 0: any and all of these are entitled to be on the road and are potentially hazards that the driver must respond to. So "going at the same speed as everyone else" is a meaningless concept

It is simply bollox of course. JamesMorgan won't be able to provide any research supporting his claim that the 85%ile is the safest speed at which to drive, because there isn't any. If he looked at the research (by which I mean real research, carried out using robust methods and subject to peer review) he'd see that lower speeds reduce both the probability and severity of crashes, full stop, which is why 20mph zones are successful at reducing causalities:
http://www.bmj.com/cgi/content/full/339/dec10_3/b4469.

 

[JamesMorgan]

Just to be clear, I am not claiming that 85%ile is the safest speed - just pointing out that if it is perceived to be by other drivers then it does create a personal dilema between individual safety and safety of others. I have no idea whether the research quoted on safespeed re the 85%ile safety stands up to peer review. However, from personal experience I do know that driving at a slower speed to the 'normal' traffic flow is potentially dangerous and can cause accidents. I do sometimes do it to save fuel, but it is stressful and does require more concentration. I could unilaterally decide to drive at 20mph in built up areas. Although this speed would be safer to pedestrians/cyclists, I personally prefer to drive at 30mph (unless road conditions dictate otherwise) as I believe it to a speed less likely to cause accidents. The only solution to overcome this is to have an enforced 20mph speed limit.

 

[adscrim]

Just to be clear, I am not claiming that 85%ile is the safest speed - just pointing out that if it is perceived to be by other drivers then it does create a personal dilema between individual safety and safety of others. I have no idea whether the research quoted on safespeed re the 85%ile safety stands up to peer review. However, from personal experience I do know that driving at a slower speed to the 'normal' traffic flow is potentially dangerous and can cause accidents. I do sometimes do it to save fuel, but it is stressful and does require more concentration. I could unilaterally decide to drive at 20mph in built up areas. Although this speed would be safer to pedestrians/cyclists, I personally prefer to drive at 30mph (unless road conditions dictate otherwise) as I believe it to a speed less likely to cause accidents. The only solution to overcome this is to have an enforced 20mph speed limit.

Who is actually to blame is you driving at 20 mph resulted in an accident? Is it not the responsibility to of those around you to drive with due care and attention? I know you're just being theoretical but if Driver B is involved in a crash because of frustration caused by Driver A's lower speed, then Driver B is at fault- no?

 

[Bad Company]

All it does cause is the occasional idiot on my bumper. They don't bother me at all.

They should. They are bloody dangerous.

I had an HGV do that to me a while ago. I was keeping the 30 limit thru a village on the way to work and I guess he wanted to maintain his momentum. He was flashing his lights and all sorts. Very intimidating and very dangerous.

 

[skrx]

I could unilaterally decide to drive at 20mph in built up areas. Although this speed would be safer to pedestrians/cyclists, I personally prefer to drive at 30mph (unless road conditions dictate otherwise) as I believe it to a speed less likely to cause accidents.

Accidents isn't the same as injuries, and I reckon that driving at 20mph on a 30mph limit road, causes less-severe injuries overall, even if the number of accidents is larger (which it may or may not be, I don't know. Most of the time I'm in 30mph areas I'm being followed by cars going at less than 20mph and it doesn't seem to be a problem).

 

[Bad Company]

HGVs maybe, yes. But I'm not too bothered about an idiot ramming me up the chuff with the likely small speed differential. They'll be the ones paying after all. And, again other than trucks, I don't really find them intimidating.

As I said you should be bothered because it's dangerous. If you have to stop quickly and the bloke behind you can't you can receive a whiplash injury or worse still he can push you into the danger.

Example - You are driving at or below the limit with a another car a couple of feet from your rear bumper. A child runs into the road and you hit the brakes stopping just short of the child. The car behind cannot stop, runs into the back of you and . . . . .

Not much you can do about it though.

 

[adscrim]

HGVs maybe, yes. But I'm not too bothered about an idiot ramming me up the chuff with the likely small speed differential. They'll be the ones paying after all. And, again other than trucks, I don't really find them intimidating.

Assuming they have insurance!

 

[Bad Company]

Assuming they have insurance!

A brave assumption imo.

 

[al78]

As I said you should be bothered because it's dangerous. If you have to stop quickly and the bloke behind you can't you can receive a whiplash injury or worse still he can push you into the danger.

Example - You are driving at or below the limit with a another car a couple of feet from your rear bumper. A child runs into the road and you hit the brakes stopping just short of the child. The car behind cannot stop, runs into the back of you and . . . . .

Not much you can do about it though.

Ultimately, you have no control over other people.

In the scenario you describe, it is highly likely the child will escape with minor injuries since if the driver behind shunts you into the child, you will hit the child at a very low speed (<10 mph).

 

[GrasB]

Actually what's more likely to happen is you hit the brakes, get down to 10-15mph then have the car behind hit doing 5-10mph more than you pushing your speed back up again & extending your braking distance a fair way as you foot will most likely be jerked off the brake by the impact.

This is why I got into the habit of using the fly off handbrake as well as the foot brake when doing an aggressive braking/emergency stop. While the effect brake on braking was minimal under normal condition the natural action of a rear impact would be to pull the handbrake on harder which would help compensate for the reduction of foot brake input. Well that was the theory anyway, I never found out if it really worked or not.

 

[GrasB]

I wasn't arguing about keep the speeds up regardless. I was more giving a good reason why it isn't just speed limits that need to be enforced but also dangerous driving by tailgating needs to be addressed as well. It also illustrates why when you're being tailgated you need to extend your estimated stopping distances.

 

[Nigel-YZ1]

The enforcement of road standards by totally mechanical means has led to the belief that slowing people down will stop all the evils of the world.

Keep the cameras running - doesn't bother me, but can we finally get some eyes on the road to deal with the bigger dangers too?

We have a generation that KNOWS that they are immune as long as they slam on the brakes at the little yellow boxes. So the one-handed driving, slouched, handbrake-turning, farty exhausted, drunk, drugged, uninsured, tailgating, gross-speeding, bullying, chance-takers only have to obey one law for 25 yards at a time, and god help the rest of us.

 

[jazzkat]

I've not looked in here for a while, I seem to have stirred up a hornets nest linking to safe speed. Apologies.

I don't agree with the politics of the site, it was the 85 percentile thing (I googled) It is one of the things that stuck in my mind about setting speed limits. Whether its true or just the motoring lobby's take I know not, but it did stick in my mind.

My take on speed is that you must be in control of your vehicle and be able to stop in the distance you can see to be safe. Not as easy as you think and painfully slow in many circumstances. Try it the next time you are out driving, you will be surprised, even on the bike there are a few descents in 30 limits where I can easily get up to 30 and I know if a car came out of a side road I'd be toast. I do it because I ride very early in the morning in a very small rural town, no excuse, but no different from many motorists. We take the risks WE perceive to be ok and some people are less risk averse than others.

The only real answer is for everyone to take regular retesting to a higher standard than the current test. A few years ago I took my IAM test and was surprised and pleased in equal measure about the quality of my motoring. Everyone should have to do it, combined with a police force that is actually able to enforce the laws we have on the statute books, I reckon we could have one of the best and safest road networks in the world IMHO

 

[JamesMorgan]

I don't agree with the politics of the site, it was the 85 percentile thing (I googled) It is one of the things that stuck in my mind about setting speed limits. Whether its true or just the motoring lobby's take I know not, but it did stick in my mind.

Like you, I'm not sure about the 85 percentile research but intuitively it feels right. However, all this means is that in order to travel safely, you should be travelling at a similar speed to the rest of the traffic. The purpose of speed limits (and more importantly enforcing them) is to determine what that speed should be. Drivers are not always a good judge of what a safe speed is, especially if it on a stretch of road unfamiliar to them. Unfortunately having inappropriate speed limits (esp too low ones) leads some drivers to believe that speed limits are not useful and to ignore them in all situations. Whilst safespeed seems to draw conclusions from this that it is better to set speed limits at the speed that most drivers want to drive, I suspect a more useful conclusion is to force drivers to drive at the speed that is optimised for safety.