Safe Speed Forums

It's true to say that more speed does increase the probability of a collision with another road user, because - due to braking distance increasing by the square of speed - you have a greater probability of being in the wrong place at the wrong time (the wrong place being anywhere within your total stopping distance of a hazard, and the wrong time being when that hazard is in your path) As such, your risk increases less than linearly with speed, ie twice the speed increases the risk less than twice.
If there are few or no hazards, or potential hazards, then your risk is pretty damn close to zero - and twice a very tiny risk is still a very tiny risk.
When and where the level and/or intensity of hazards, or potential hazards, is high, then the risk is high and so any small gain/reduction in risk becomes significant - which is where the SafeSpeed rule comes in.

But it's misleading to say that such and such a collision could have been avoided simply by going slower - and such an argument certainly has no rightful place in a court of law.

Cheers
Peter

I know exactly what you're talking about and I've done it myself. I was really just pointing out (rather obtusely, I'll concede) that the original post contains virtually nothing about the circumstances of the incident and that many assumptions about the behaviour of motorcycles (both in terms of the laws of physics and how they are ridden) on the roads are incorrect.

To compoud the issue, when travelling in a straight line the laws of motorcycle physics dictate that before you can swerve left, the point of contact on the road must move to the right - ie. towards that which you are attempting to avoid.

I was also attempting to present reasons why avoidance of the car may not have been a priority. Perhaps the rider in question made the (erroneous) judgement that the car would return to its own side and traded that probability off against what he thought would be a certain crash taking avoiding action.

Who knows, but I still find the judgement somewhat akin to saying that if you hadn't accelerated so quickly from the traffic lights you wouldn't have been T-boned by the lunatic that ran the red.

Double speed equals four times breaking distance and double thinking distance. For high speeds braking distance plays a substantially greater part than thinking distance. I suggest therefore that, for a given visual acuity, the risk may actually increase greater than linearly?

None of the above condones the comments by the judge.

There is a possibility here which has not been mentioned.
If the motorcyclist was in the position on the road because he was passing an obstacle - displaced road cone, debris in the road etc., then the Judges might have assumed that he should have been prepared to stop, rather than ride around it, but his speed made this impossible, even if it were below the limit.
As Paul says, we are relying on the reporting, and not the facts.

One other thing
Actually he might have been stationary, AND have been run down by an inattentive Clio driver!

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Time to take responsibility for our actions.. and don't be afraid of speaking out!

That's only half the story. The laws of probability also come into the equation (conveniently ignored by TRL, etc)
If you have two points along the road spaced, say, 10 metres apart, the probability of you being between those two points at a given time halves as you double your speed.
So it's four times divided by two = twice the risk for the braking part, and double divided by two for the thinking bit.
If you do the maths you'll find that the overall risk is proportional to thinking time plus half braking time.

Cheers
Peter

I guess I will get my head around this one - but it surely applies to the prosepctive victim not the driver? If a stream of pedestrians are crossing the road, ignoring traffic completely, leaving just enough room at any one time for you to get between them with a foot or so to spare between the back of the one just past and the front of the one just coming, the probability of you being able to get between two rather than clobber one will have an optimum speed (faster - less chance of one walking into the back of your car, less chance also of you getting it right by getting between them. Mind you, if you go faster, you have much less chance of getting a cannon

This report was clearly of an insurance liability case, from a collision in April 2002, and published as part of an "unfair to bikers" article. The other cases quoted were all in the 1960s!
I understand the mechanics of riding on two wheels of both the motorised and non-motorised varieties. I am pleased to say that only once in a car have I had to get out of the way of a biker with his/ her wheels to the left of the centre line but his/ her head well to the right of it.

It applies to both.

The only proviso is that the time between hazards is longer than the exposure time - but this is (almost) always the case. You're hardly likely to have two pedestrians independently stepping out in front of you within your stopping distance, and if that did happen then the two could be counted as a single hazard.

Cheers
Peter

If the corner was sharp enough to require the biker to lean across the centre line then the oncoming traffic would also be far more likely to be close to the left side of the road to make a smoother line.

I have regularly come across bikers doing exactly this when travelling on twisty roads and have never found it to be a problem. I know not everyone "apexes" corners but for those that do the rider could be almost completely on the wrong side of the road and still have plenty of room.

Still, better to be safe than sorry and stay on your own side of the road....

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Ross

Yes I'm a hoon, but only on the track!!!!

I once heard it mooted as "imagine what would happen if you met yourself coming in the opposite direction..". To which the "flip" answer was of course, "That'd be OK then, we'd both be on the wrong side of the road"..

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"Politicians are the same the world over... We build bridges where there aren't any rivers." - Nikita Kruschev

The original post asked if we believe a bias exists .

I think willcove somes up what I see IMHO as the answer , he starts his argument with a sweeping statement about "all" bikers , then once challenged , it becomes "some" bikers , then miraculously , (presumably once the head of steam is up again ) , ups his estimate again to " many bikers .

In my 17 years experience in many forms of transport (motorcycle being the primary one ) I have encountered good and bad in all forms . I don't believe sweeping generalisations help anybodys argument but in closing I have heard the term " bloody bikers " far more than any other endightment , make what you may of that .

Dik

You have that back to front. Most studies show that risk increases more than linearly with speed.

Try it for yourself. Pull into your drive at 15 mph, avoiding the children and the plant pots. Next, pull into your drive at 30 mph, and check how much damage you have done. Lastly, pull in at 60 mph, remembering to wear your seat belt this time. And open the garage door, else you’ll knock it down.

If your car is still driveable, repeat the experiment several times, and put the results up on this web site when you are quire sure that the risk of crashing when pulling into your drive at 60 mph is somewhat more that 4 times the risk at 15 mph! Good luck - you'll need it!

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I stole this .sig

Although that is true, it is irrelevant.

That is because you do not know in advance which 10 metres stretch will throw up a hazard. Although if you double your speed, you halve the time in a given road space, you cover (and are therefore exposed in) twice as much road space. Taking it to extremes, if you pass between two points at infinite speed, you do not miss all the obstacles in that space! You hit them all.

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I stole this .sig

But in the real world it is demonstrably false. See:

http://www.safespeed.org.uk/percentages.html

For your driveway example to be realistic, we'd have to find a driver who was prepared to drive in such a manner. Clearly they don't do that, and there's a reason - they are trying not to crash.

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

If you want to bring in new terms , go ahead. As long as you concede that, all things equal, risk increases more than linearly with speed.

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I stole this .sig

Oh, FFS, give me strength!

Try to understand what you read before you start sprouting mindless drivel!
That's, of course, assuming you're capable of understanding - some of us here take lateral thinking for granted.

Only irrelevant in the never-never land which you inhabit.

Sometimes I don't know why I bother.

Will do, just after you concede that 1+1=3, and that black really is white.

All things? Including the margin for error that a real world driver allows himself? No mate. It's not only under linear, it's negative. faster roads are safer.

From TRL511:

"A typical speed-accident plot for data from a range of heterogeneous roads tends to show a negative relationship between accidents and speed.

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety