Safe Speed Forums

Steve

Here's one for you:

Of all drivers who have ever driven in a F1 Grand Prix, more than 10% of them have first names which begin with a 'J'.
And when it comes to world champions, more than 30% of them have first names beginning with a 'J'.
Even better, no fewer than nine GP drivers (out of around 600) have the initials 'JS', three of whom have been world champions (out of 26)
I'm not a statistician, but it seems to me that those figures are far higher than one would expect from random selection, and so there appears to be quite a strong correlation.
However, I defy anybody to suggest that the relationship is a causal one.

Cheers
Peter

_________________
Only when ideology, prejudice and dogma are set aside does the truth emerge - Kepler

It could be causal, though - it might be that some countries are over-represented due to the popularity of the sport in them, opportunities there etc. Perhaps a first name beginning with J is more common in these countries? Certainly more analysis would be needed. As an example of national differences, consider how much better Australia does in swimming competitions than GB, despite having only a third of the population. I'm sure you'd agree there is most likely a causal link in this case.

Of course when dealing with small numbers such as 3 champions with the initials JS, you can't infer as much. E.g. if a person entered the national lottery just once, won, and concluded that they win every time they enter the lottery, the confidence in such results varies with the number of experiments, indeed you can mathematically calculate the appropriate confidence interval. My local council makes this mistake by attaching a high statistical significance to a single accident at a particular location, often applying treatment to the road that will never be reversed, even though there may never have been a repeat occurrence without it.

Dunno that different countries would have that sort of effect when it comes to GP drivers though - it's a bit of an elitist sport anywhere.

Different nationalities are fairly well represented with no obvious bias towards particular initials.
I've pasted a list of the 26 world champions here because the complete list is too long - although this is broadly representative:

Mario Andretti
Alberto Ascari
Jack Brabham
Jim Clark
Juan-Manuel Fangio
Giuseppe Farina
Emerson Fittipaldi
Mika Hakkinen
Mike Hawthorn
Damon Hill
Graham Hill
Phil Hill
Denny Hulme
James Hunt
Alan Jones
Niki Lauda
Nigel Mansell
Nelson Piquet
Alain Prost
Jochen Rindt
Keke Rosberg
Jody Scheckter
Michael Schumacher
Ayrton Senna
Jackie Stewart
John Surtees

There are also two DH and two MH, besides the three JS.

Cheers
Peter

_________________
Only when ideology, prejudice and dogma are set aside does the truth emerge - Kepler

Quite the opposite the mechanism is quite clear in most: The linear relationship between thinking time and speed as well as the square law relationship between braking time/distance and speed. When coupled with the drivers ability to react and avoid accidental collision the mechanism is established very clearly.
The fact that it may be denied by some is perhaps more difficult to understand than establishing the causal mechanism for denial. That is most obvious.

Oh, I understand that only too well - although you appear to demonstrate a certain ignorance when you start talking about a linear relationship between thinking time and speed, and when you say there's a square law relationship between braking time and speed.

I also understand that it's largely irrelevant - which is something you don't seem to be able to get your head around.

BTW where is that link I asked for?

Cheers
Peter

_________________
Only when ideology, prejudice and dogma are set aside does the truth emerge - Kepler

Answered yesterday:
http://www.safespeed.org.uk/forum/viewt ... 5622#35622

No real word data fits the assumption. Ergo the assumption is false.

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

You can find random coincidences anywhere, e.g. if I consider the list of one person that is me, 100% of those people have my initials! Amazing! And if we pick me and one other person we can probably find some other coincidence. The point is that it is one thing to take a set of data, and look for something, anything, that seems unusual, it is quite another to take factors that are already believed to be of interest and study their relationship.

Now, the point you have made before, and I guess that perhaps you are making again here, is that you believe there is no reason for someone to be interested in the link between speed and accidents in the first place, as there is no reason to suspect they are linked. I have to disagree, and I suspect that you do not practise what you preach and drive everywhere as fast as you possibly can. I'm guessing that you ease off the throttle, or even apply the brakes at times. Surely this is because you believe it would be dangerous to simply set off on your journey, plant the accelerator into the floor, and keep it there until you reach your destination? Surely we have to conclude, therefore, that you believe increased speed is dangerous? Or are you going to tell us that the only reason you don't drive everywhere at a steady 100+mph is fear of speed enforcement?

Ahh, this is to do with the definition of 'speed'. 'Speed' is two almost entirely different quantities and you're using them interchangably.

Firstly there's appropriate speed. It's not easy to define, changes constantly, has no units, yet road safety entirely depends on it. You can never tell if a speed is appropriate (or safe) by reference to a speedometer.

Secondly there's 'numerical speed'. We can always define it. It's a physical quantity, it's measured on speedometers. Yet it gives us no clue about safety. Frequently very modest numerical speeds are deadly.

Pete is saying that there's no relationship between real world numerical speeds (as selected by drivers) and safety. Yet the relationships between appropriate speed and safety are clear and strong.

Numerical speed is used in law as a very weak proxy for appropriate speed. Yet the road safety establishment seems almost incapable of making the distinction.

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

I would dispute that "speed" is two different quantites. It has a physical definition, as what you are calling numerical speed. The question of whether a numerical speed is appropriate or not in the context of a particular driving situation is a separate issue. But regardless, I understand your point

I have a few comments, though:

1. To say, effectively, that you can drive as fast as you want, provided it's safe to do so, is a self-defining truism.

2. The statement that numerical speed doesn't cause accidents, only inappropriate speed, is a corollary to this self-defining truism.

3. Personally, I'd rather have numerical speed limits than a system based entirely on a police officer's discretion. With numerical limits I can guarantee my safety (the biggest threat to my safety, when driving along, statistically speaking, is that of receiving points and a fine for speeding, as the number of such events far outweighs the number of accidents), but with a system based on discretion I have no way of knowing for sure that a police officer will agree with my view that my speed is appropriate.

4. The courts are incapable of satisfactorily enforcing other laws where the science is even remotely complex, e.g. take this quote from here:
http://news.bbc.co.uk/1/hi/uk/4705939.stm
"They'll be looking for fragments of DNA - we know that people have been convicted of robbery on one hair or fragment of dandruff - so these are very powerful investigative tools."
People shouldn't be convicted of anything based on a single hair! It's ludicrous that this happens, and I would hate to have driving prosecutions drawn into the same mess. It's bad enough that they can't accurately measure numerical speed, and the courts can't satisfactorily assess arguments regarding the accuracy of a measurement, just imagine what would happen if the system were based solely on a police officer's judgement as to whether the driver's speed was appropriate or not. The police officer's word would have to always win, otherwise the system would be unworkable, so there would be no point anyone ever contesting it in court, as they would always lose. So what we would have is a system where a police officer can have anyone they want convicted of driving at an inappropriate speed.

Broadly I am in agreement with this. Indeed it is how it used to be when speed limits were enforced by BiB rather than scameras.

One could not be prosecuted for speeding then and now if one was below the limit. However, driving carefully at OR AROUND the limit when it was safe to do so would not attract attention of plod, but often it does set the yellow money-boxes chinking.

I think I can say with certainty that SafeSpeed is NOT against speed limits. They have their purposes. Of course speed limits for social reasons have a different purpose and that is debateable. Those that have been lowered solely or with the main effect of increasing revenue are to be deplored. I contend also that the message from SafeSpeed accepts and agrees that the speed limit law is an absolute law and if a prosecution is brought for a speeding offence that the accused should face the music.

What SafeSpeed is wholly against is the routine and absolute enforcement of these limits. That gives the wrong message and criminalises the wrong people. Return to judicial enforcement with a rolling knee rather than the absolute cutoff of the camera threshold whatever it is. By rolling knee I mean a grey zone where police have absolute power of arrest or ticket, but that they would prefer to educate rather than prosecute where appropriate.

It is an interesting observation on this point that the Montana experiment in derestricted rural highways was brought to an end because the courts objected to giving the police absolute discretion as to judging what was a "reasonable and prudent" speed. They pulled over a guy doing 95 mph in a Hyundai Accent or similar and gave him a ticket because in their judgment his speed was not "reasonable and prudent" in the circumstances. He took it to appeal and won his case.

_________________
"Show me someone who says that they have never exceeded a speed limit, and I'll show you a liar, or a menace." (Austin Williams - Director, Transport Research Group)

Any views expressed in this post are personal opinions and may not represent the views of Safe Speed

People I know who want to drive at or below the speed limit often say that the biggest problem they face in attempting to do so is other drivers who want to go faster, and hence are close up behind them, trying to get past at inappropriate points. There are two ways I can think of to solve this problem - either allow the slower drivers to speed up to a reasonable speed (without fear of prosecution) or prevent the faster drivers from driving faster, i.e. blanket zero tolerance enforcement.

As I said in another thread, I believe speed differentials are more important than is generally recognised. On multi-lane roads, I believe it is healthy to have moderate differentials between vehicles in different lanes. On single lane roads where overtaking is undesirable, I believe it is best to have everyone wanting to drive along at the same speed - there's no point tailgating someone when you have no desire to drive faster than them. An external constraint such as speed limit enforcement would be one way to get everyone wanting to drive at the same speed in these cases.

Incidentally, I find humps to be one of the worst things for causing people to dive past other cars - different cars have hugely different abilities to negotiate humps, and this causes a large difference in desired speed, in a situation where I believe it is most healthy to have vehicles wanting to drive at the same speed.

How would you fell about terms like 'absolute speed' and 'speed relative to circumstances?

My point, which I wish to stick to like glue, is that we (society) frequently confuse different quantities and effects of speed. There's no general relationship, for example, between speed in miles per hour and safety. Yet there is a strong relationship between appropriate speed and risk. Almost everyone fails to make the distinction and much rubbish is talked as a result.

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

Personally I would be happy with the term "speed" being used according to its scientific definition, and the term "appropriate speed" seems satisfactory for how you want to use it.


Yes, clearly there is a strong relationship between appropriateness of speed and risk, I doubt anyone would dispute that, as it's arguably true simply by definition.

I do, however, question the statement that there is not a general relationship between speed in numerical terms and safety. Many of our roads have broadly similar characteristics that make similar speeds appropriate. For example, if I advocated driving everywhere at a constant speed of 200mph, you would probably agree that this speed is unlikely to be appropriate on our roads. 500mph is even less likely to be appropriate, but 50mph is more likely to be appropriate. So there is a general relationship between speed in numerical terms and the appropriateness of that speed. The fact that drivers are in practice quite good at choosing an appropriate speed, I feel, backs up my view, as to accept the notion that drivers are restricting their numerical speed to appropriate levels is an implicit acceptance that higher numerical speeds would be inappropriate.

I think the point is that there is not a strong relationship between actual speed and safety, because in general drivers choose safe speeds in the first place, and slow down in hazardous areas.

_________________
"Show me someone who says that they have never exceeded a speed limit, and I'll show you a liar, or a menace." (Austin Williams - Director, Transport Research Group)

Any views expressed in this post are personal opinions and may not represent the views of Safe Speed

That's not what I'm saying at all, and I now feel at quite a loss as how to put things any clearer than I have done.

So here goes, maybe this will make things a bit clearer, maybe it won't.

Of all the research papers I've seen to date, only a few even attempt to describe a mechanism linking speed to collision risk, and that mechanism is always the same - braking distance is proportional to the square of speed, ergo collision risk is roughly proportional to the square of speed (deviating only because of reaction time makes 'reaction distance' directly proportional to speed)
As if it isn't bad enough that this hypothesis is demonstrably wrong, they then exaggerate this supposed effect by making unrealistic assumptions, such as braking deceleration is 0.6g and average reaction time is 1.5 seconds!

This hypothesis also spawns other falsehoods such as, going slower gives you more time to react, and that there's a direct link between free travelling speed and collision speed.

But this hypothesis is accepted without question, it pervades current mainstream thinking, and if real-world statistical data doesn't agree with it, they manipulate the data until it does, as well as making inferences from the data which simply don't exist.

The true relationship between speed and collision risk is that the risk is proportional to exposure, ie the amount of time it takes to cover your total stopping distance at your travelling speed - which gives a less than linear relationship between speed and collision risk (the deviation being due to reaction time, which is independent of speed)

But even this model is largely irrelevant in the real world, and merely serves to place an upper limit on risk - which is still much higher than real-world data would suggest.
It would only apply if, a) everone always drives at a fixed speed (whatever it happens to be) regardless of conditions, b) they only ever react to hazards when they are already directly in their path, and c) hazards always materialise instantly out of nowhere.
But drivers don't drive like automatons - they slow down, and adust their positioning and spacing, for hazards (real, perceived or potential) so they are able to deal with them. And, contrary to what some people would have us believe, they generally have plenty of time in which to make these adjustments. This driver attention-hazard-speed feedback loop effectively removes speed from the risk equation, and so we now have essentially two significant factors:

1) Drivers aren't perfect - they make mistakes. they sometimes aren't as attentive as they should be, and sometimes misjudge the appropriate speed for conditions. But, even then, it can be shown that the latter error is definitely the lesser of the two evils.

2) The frequency of hazards. The more hazards you encounter the more likely it is that a mistake is going to result in a collision. But it's also true that, because most hazards are transient - the ones that exist only at a particular time at any particular place, the more time you spend on the road the more hazards you will encounter, on average. And the lower your average speed is the more time you spend on the road.

Just to illustrate how far current thinking is divorced from reality:

We are told that we're perfectly safe driving at 30mph, but at 35mph we will mow down every pedestrian in sight.
From 30mph you need roughly 21 metres to react and stop, and about 27 metres from 35mph.
That much is true.

But:

1) We are expected to believe that, not only do pedestrians always charge into the road when there's a car about 24 metres away (never, say, 30 metres or 15 metres), but that a driver will only ever see said pedestrian when they are about 24 metres ahead of them, in which case they'd better be doing no more than 30mph, or the pedestrian is dead meat.
But, hang on a mo, isn't the minimum eyesight requirement for a driver to be able to read a numberplate from 22 metres? Given this, isn't it reasonable to say that if the driver doesn't see that there's a pedestrian just about to step into the road from a good deal further than 24 metres, then they are either legally blind or simply not looking? And that if conditions are such that the pedestrian can't be seen from more than 24 metres then the driver shoudn't (and, in all probability, won't) be doing anywhere near to 30mph?
The distance between two street lights is normally 50 metres, for the sake of comparison. So a visibility of 50 - 100 metres or more is commonplace - and such a distance gives you more than enough time to spot hazards and comfortably adjust your speed etc as appropriate.

2) Just half a seconds inattention on the driver's part can make a difference of more than 6 metres to their stopping distance - more than cancelling out the supposed advantage of going slower.

3) There is a strong inference that , if you're driving at 35mph, the pedestrian will be hit at 35mph. This is complete nonsense, of course - the collision speed being a function of how long you've had your foot on the brake before impact. Here, a half a second makes a difference of around 10mph.

4) The time you have available to react depends on how much time the hazard gives you, and your attention. It has nothing to do with your speed. Your speed only decides how much time you require to react - a subtle but important point. It is for this reason that slower roads are slower - because they're more hazardous. And why people travel faster on roads with fewer hazards. It's also why slowing down fast traffic on fast, safe roads doesn't make them any safer. It's also why you seldom see speed enforcement on slow, hazardous roads - people are already driving slowly.

I hope this rather long posting has made things clearer.

Cheers
Peter

_________________
Only when ideology, prejudice and dogma are set aside does the truth emerge - Kepler

Pete, thanks for the lengthy post. I agree with most of what you said, and as I've said before, I do think that we largely share the same understanding of the underlying maths/physics behind it all, I think it's just the way things are sometimes worded that I have difficulty with. In the above case, I think it's the word "speed", where I think what you in fact mean is "appropriate speed", i.e. you are building in an assumption that people are slowing down for hazards. As I've said before, it's a self-defining truism that it is safe to drive at an appropriate speed, and that risk is not increased by driving at a numerically greater speed when appropriate. So for this reason, I don't see this point as being of relevance, it's simply stating the obvious, and I don't believe it is what most people would understand by the term "speed". What is of interest is what happens when we have an accident situation, where someone has made an incorrect judgement about what is the appropriate speed, or when someone doesn't see a hazard, and hence their previously appropriate speed becomes inappropriate. If everyone always selected an appropriate speed, we would have no accidents, but we do have accidents, so therefore some people must be selecting inappropriate speeds, and the question is how do we get people to change that. Of course, a truly appropriate speed might be extremely slow in some cases, for example you would have to slow down to a huge degree whenever you pass a parked vehicle, perhaps to around walking speed.


Ah, now I think I'm seeing what you're saying. You're saying that assumptions a, b & c define a worst case scenario for a link between numerical speed and risk of accident. These assumptions result in a very simple mathematical model, so we can calculate the risk from that, and that must be our upper limit for the risk arising from speed. Lets assume those assumptions do indeed represent a worst case, they're certainly good enough for the sake of this discussion.

The problem is that we aren't interested, generally in the risk of an accident, we're interested in the risk of an accident of a particular severity. This is no longer so simple to calculate that I can do it analytically, but can your computer model do it? E.g. if you plug in a constant speed of 40mph, can you find out how many impacts of 20mph or greater result, then do the same at a constant speed of 80mph? The relationship between speed and risk of accident may well be different to the relationship between speed and risk of accident of a particular severity or worse.

But, surely then, the best limit would be just higher than the speed most people would choose to drive at in the absence of a limit? (the 85th percentile?)
That way, most people would drive at a comfortable and safe speed without exceeding the limit.
Let's face it, one of the big reasons you'll see so many people driving at 45-50mph on an NSL road where 70mph would be appropriate, is because they've being conditioned into believing that, as it's dangerous to exceed the limit, they'd best give themselves a comforable margin - and, by inference, anyone who desires to overtake them must be some kind of nutter who believes in living on the edge.
And it's simply no fun driving behind someone for a long distance, even if they are driving at the limit. Besides the fact that it's probably below your 'comfort' speed, their speed does vary (say, by plus/minus 5mph) so you're also having to adjust your speed every few seconds in order to maintain the gap - so you end up paying far more attention than is healthy to the back of the car in front. This is, at the very least, tiring.
And if you have a queue of cars, a small speed variation of the front car is all too easily amplified into a very large variation at the back of the queue.

Cheers
Peter

_________________
Only when ideology, prejudice and dogma are set aside does the truth emerge - Kepler

No, I was still talking about the simple relationship there, as I think you recognised in the second part of your posting.



Yes, this is easy to plug into the model - and the results bear out my assertion that mistakes in speed are less costly than mistakes in attention.
Whereas a mistake in speed makes a more-or-less proportional difference to average impact speed (which could still be anywhere between zero and the full travelling speed for a single incident, only averaging out over a statistically large number of incidents), a mistake in attention (hazard awareness) makes a difference to the maximum impact speed.

Cheers
Peter

_________________
Only when ideology, prejudice and dogma are set aside does the truth emerge - Kepler

I'll accept the point that inattentiveness may be worse, no problem there. But if average impact speed is proportional to free travelling speed, that could have a very disproportionate effect on the number of serious accidents. So what result do you get, say, for how the number of accidents where the impact speed is 30mph or greater, say, varies with free travelling speed? From what you've said, I would expect a more than linear increase in this measure with speed.