Safe Speed Forums

Maybe sticking additional obstacles at a junction makes the driver concentrate on not hitting the obstacles, when they'd normally have thier thumb up thier bum, and their mind in neutral.

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So either way, how exactly does that benefit the pedestrian trying to cross the road at this junction? The observant driver is having to divert some of their observational time to checking the bollards, making them more likely to miss a pedestrian, and the thumb-sitting driver, who wasn't looking out for pedestrians at all to begin with, still isn't looking out for them... As I see it, that actually makes things worse on average

Thanks for the explanation Twister, I didn't realise the pavement would be extended as well as the introduction of the bollards. I see where Pete's coming from as far as that's concerned.

I suppose it could be argued that the slowing down of the driver would reduce the risk more than the increased risk of the pedestrian stepping into the road. But I'm not going down that particular route!

It might be easier if you think of the concrete bollards as tough pedestrians! Drivers habitually calm down once they have side swiped a few of them!

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If a road has been narrowed to little more than a vehicle's width, then the moment a pedestrian steps off the pavement they're in the path of any vehicle which happens to be there at the time.
How long does the pedestrian take to step off the pavement from a standing position? A quarter of a second? Less, perhaps?
So you have a pedestrian standing near the edge of the pavement, looking the other way perhaps, and they step off the pavement just as a car's coming along. If that car's doing just 10mph and it happens to be within about one car's length of the pedestrian at the time, then that pedestrian is going to be hit - and probably at the full 10mph, unless the driver is possessed of Schuhmacher-type reflexes.
And if that can happen, it will happen.
Exacerbating this is that, because a vehicle takes longer to cover a particular distance at a lower speed, and also because at a lower speed there's less physical gap between vehicles, it's more likely that there's going to be a car within a car's length at the time the pedestrian steps off the pavement.

If you don't understand how that works, please read it again.

Cheers
Peter

I noticed another problem to-day with these pavements.
The give way line for traffic coming from a side road and joining the main road has been painted on the side-street-side of the psuedo pavement. (It couldn't be painted anywhere else really). This means a car stopped at the give way line can't see the main street traffic properly.

These lines have just been painted in the last two days and I have already seen different strategies to get over the problem. Mr. Magoo waits at the give way line indefinitely, waiting for who knows what. Others sensibly stop on the pavement so they can see properly.

The more sensible approach is now at odds with the highway code! I really am getting annoyed with this whole thing.

No, they're not. Far from it.



It's only been made safer because there's no traffic anymore.
For the little bit of traffic which remains, it's now a lot more dangerous to pedestrians.

Wake up and smell the coffee!

We live in a universe of infinite possibilities. Somewhere there is a version of planet Earth which is inhabited solely by drivers with Schumacher-like reactions.



Nope you've lost me with this one. I've re-read half a dozen times. If a vehicle takes longer to cover a particular distance at a lower speed, the driver has more time to depress the brake pedal, surely? I'm not sure why the other vehicles present would have any impact either? I was under the impression the scenario was a single vehicle turning into a side street and a pedestrian crossing the road. Unless in this case the pedestrian is being treated as vehicle?

A couple of years ago they changed one of the streets in Bristol centre to a bus-only lane, and reduced the width of the road to the width of a bus, and then blurred the distinction between the road and the pavement.
Since the did that, pedestrians have been regularly hit by buses - at least two of them fatally. This was a very rare occurrence previous to the changes.
They then put in a 20mph speed limit. Nothing changed.
They then made some cosmetic changes and moved the pedestrian crossing a small distance down the road, to try to fix the problem. This made no difference. The day after they finished another pedestrian was fatally injured by a bus.

When will they learn?
You don't make roads safer by making them more dangerous.

Cheers
Peter

I think you took that out of context (I did see the smiley, BTW)



You don't know when a pedestrian is going to step out, and you don't know how far you're going to be away from them at the time. These things are completely random.
If you're doing 20mph and you're two car lengths away at the time, you've got one second to react and stop.
If you're doing 10mph and you're one car length away at the time, you've got one second to react and stop.
And, in either case, the less time it takes for the pedestrian to step into the road, the less of that one second you have to react and stop.



If you do have a string of vehicles (which you often do), then the slower they're travelling the less the physical gap between them (for the same 2-second gap) so the more the immediate piece of roadspace is occupied by vehicles, so the greater the probability that there's going to be one within a car's length at the time you step off the pavement.

Cheers
Peter

You forgot to say that if you're doing 10mph and you're two car lengths away at the time, you've got two seconds to react and stop, which means that slower is safer.

Look, it's easy - try it for yourself next time you are in a crowded pub. Each time you return to your table with your drinks, rush back as fast as you can and see how many drinks you spill over people! Then (assuming you don't get battered), walk back normally - you'll have much more beer in your glass that way!

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I understand the theory now Pete, thanks for the explanation.

Just out of interest, is this theory a widely accepted one? I can see it happening at speeds in excess of say 25mph (arbitrary figure, just for the sake of argument) on relatively straight roads, but would have thought that other factors would come into play in lower speed urban areas with junctions hairpin bends and the ilk?

There's no way of knowing whether you're going to be ten car-lengths away or a quarter of a car-length away.
But, by the laws of probability, you're just as likely to be one car-length away at 10mph as two car-lengths away at 20mph - because, in both cases, your exposure is one second. And you're just as likely to be four car-lengths away at 20mph as two car-lengths away at 10mph.
The length of time it takes the pedestrian to get into your path, and the length of time it takes you to react, are the real factors deciding risk.



Apples and oranges. Not the same thing.
By the same token it must be safer to fly a plane at 50mph than at 500mph

Cheers
Peter

It's plain, vanilla physics and probability.
Of course there are other factors, in certain places, and all of them have different effects because of different mechanisms.

Cheers
Peter

I'm talking about a specific case where you're two car lengths away at the time. If you are doing 10mph and you're two car lengths away at the time, you've got two seconds to react and stop. If you are doing 20mph and you're two car lengths away at the time, you've only got one seconds to react and stop, making it more dangerous.

If you want to talk about another specific case where you're (say) three car lengths away at the time, or 4 or five car lengths away at the time, you've STILL got more time to react and stop when going more slowly. Don’t you?



Oh yes they are - it is planes that are different! They have a massive overlook system of air traffic control to ensure zero contention via separation planning. I have NO problem with using technology in cars to do that too – in fact I think it is inevitable.

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You can quote specific cases until you're blue in the face, and so can I - but it means nothing unless you establish the probability of that particular specific case actually happening, compared to the probability of another specific case happening.
I could say, "Yes, but what about the specific case where you're doing 10mph and you're two feet away when something happens?"
Or, "If I have six numbers coming up in the lottery I'll win more money than if I only have three."

Please try to comprehend what I'm saying.

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If you're in the situation where you're two car-lengths away (or one, or whatever) then yes, it is better if you're doing 10mph than 20mph.
But if you're doing 10mph then you're twice as likely to be in that situation in the first place.

I really can't make it any clearer than that, so if you still can't understand, then tough!



Cheers
Peter

It still seems a bit too simplitistic though Pete. Sure you can condense most things down to pure physics and probablility, but you're talking about dozens, maybe hundreds of different factors in this kind of interaction. Simply dictating the position of a vehicle in relation to it's speed just doesn't make sense to me (unless the external factors are kept to a minimum, e.g. motorway driving).

Yes, there are normally several factors involved in this sort of interaction, but if you don't understand the basics then you can't hope to understand how everything else fits together.



That's the kind of stuff the powers-that-be feed us all the time.
"If you're doing 35mph and a child runs out... blah blah blah"
Except in their case it's a misrepresentation of the basics - I don't know whether it's deliberate or out of ignorance.

Cheers
Peter