SSS for Von - it's why your wrong!

[safespeed]

Hi all and especially Vonhosen,

I've been fairly fascinated to see Von's arguments about the importance of the speed limit over the last few months. I've enjoyed the discussions too. Thanks.

It may be that the view here in the post will finally sort things out and prove the fundamental limitation of the speed limit system as a risk management tool.

See the article at: www.safespeed.org.uk/sss.html

It presents and explains the following 'risk equation' which was proposed by Stephen Haley.



Stephen is warning us that risk on the road is mainly a function of three parameters working together. If there's more speed there's more risk. If there's more 'surprise' there's more risk and if there's more space there's less risk. In practice, of course, all three are continuously controlled by each individual driver.

I hope examination of the materials will prove once and for all, that you cannot hope to control risk by reference to only ONE of the three parameters in Steve's equation.

[safespeed]

autismuk said:

Yes. One thing that I've never seen addressed, and I don't know why, is the concept of traffic density ; that if you reduce the speed from 60 to 40 you increase the traffic density by 50%.

The consequence of this is most obvious in roads littered with dangerous and difficult junctions ; the traffic moves more slowly but there are fewer opportunities to make the turn.

There's an Israeli (scientific) paper that explores the issue, calculates that fewer 'encounters' take place when traffic is moving faster, and suggests that this might be the reason that crashes don't rise with speed 'as expected'. It's not available on the net.

[safespeed]

apache said:

To be honest Paul I don't think he gives a rolling donut...

I think we'll break through sooner or later because he understands driving and cares about it. But we have to break through a couple of false assumptions that have been accepted for years and fitted into the framework of understanding.

Either that or he's working for the government and here to check out our arguments.

[safespeed]

safespeed said:

Hi all and especially Vonhosen,
[...]

[...]
I hope examination of the materials will prove once and for all, that you cannot hope to control risk by reference to only ONE of the three parameters in Steve's equation.

Hi Von,

No comment at all on the original post in this thread?

[safespeed]

GreenV8S said:

... Von ...

I must say it's to his credit that he is willing to keep making his case calmly and politely despite ovewhelming and sometimes quite rude opposition from the rest of us. Let's stick to discussing the issue and not let it get personal.

[safespeed]

ATG said:

safespeed said:

safespeed said:

Hi all and especially Vonhosen,
[...]

[...]
I hope examination of the materials will prove once and for all, that you cannot hope to control risk by reference to only ONE of the three parameters in Steve's equation.

Hi Von,

No comment at all on the original post in this thread?

With all due respect, why do you expect a response from anyone? There's nothing new here. Obviously those factors and many others contribute to total risk.

If you really take the assertion that Risk = Speed * Surprise / Space seriously, then you'd conclude that "partial d Risk by d Speed" is equal to the constant (Surprise / Space) i.e. risk is directly proportional to speed, which surely illustrates the fatuous nature of writing down equations like Risk = Speed * Surprise / Space when they clearly don't hold.

What on earth makes you think that you can call a pair of terms constant? Surely the experience of driving proves that the three terms are continuously dynamic and managed in real time by drivers? Did you read the supporting material?

[safespeed]

vonhosen said:

I'm not being rude, but is that supposed to be ground breaking ?

I find it ground breaking as a simple description of a complex interaction. It warns us with utter clarity that no one parameter can set or control dynamic risk. Frankly I believe that it blows your arguments out of the water. If you don't think it does, then I reckon you haven't truly grasped its 'global' significance. (Equally, I'm not being rude.)

vonhosen said:

My contention is that as people get to higher speeds (with higher risk) they mostly don't have the required skills to deal with greater surprise OR think about how their greater speed impacts on causing surprise or misjudgement by others. We already know that those same people (vast swathes of them) are ill disciplined on leaving sufficient space.

Clearly we do not have a situation where normal driving leads to the ultimate violation of Steve's equation (i.e. crashes). Crashes are rare. Yet we have situations on every single car journey where speed is varied to zero as a risk control measure.

Controlling one term in isolation in an attempt to control risk is actually pretty absurd. That's the point. Driving risk management depends on controlling all three terms in balance together continuously.

[edited to correct spelling and for clarity]

Edited by safespeed on Sunday 18th June 11:33

[safespeed]

ATG said:

safespeed said:

... Surely the experience of driving proves that the three terms are continuously dynamic and managed in real time by drivers?

Yes of course it does. That is preceisely why bandying silly pseudo formulae like Risk = Speed * Surprise / Space is stupid. All I did was to take the silly formula at face value and derive from it a result that is clearly wrong.

I think it represents a very fundamental view of the nature of driving risk management. It's a logical relationship, not a mathematical one.

[safespeed]

s2art said:

safespeed said:

ATG said:

safespeed said:

... Surely the experience of driving proves that the three terms are continuously dynamic and managed in real time by drivers?

Yes of course it does. That is preceisely why bandying silly pseudo formulae like Risk = Speed * Surprise / Space is stupid. All I did was to take the silly formula at face value and derive from it a result that is clearly wrong.

I think it represents a very fundamental view of the nature of driving risk management. It's a logical relationship, not a mathematical one.

Then dont represent it as a mathematical equation. It does your case no favours whatosoever. Classic pseudo-science presentation.

Why do you think it's presented as mathematical equation? I never did. In fact it's obvious to me that it couldn't be, despite the presence of mathematical operators.

[safespeed]

vonhosen said:

Of course drivers have to manage all of the above. They are expected to, they are tested to show that they can. Limiting speed as a control measure doesn't absolve you of your responsibility in that regard.

I don't know, Von, perhaps you need to think about it some more. I honestly don't think Steve's equation leaves any room for doubt. I've sent Steve an email inviting him here to see if he has anything to say about it.

[safespeed]

s2art said:

If it couldnt be then its even more silly. You refered to it as an equation, it looks like an attempt at a mathematical equation relating several variables, anyone who sees it would think it an attempt at a scientific relationship. Sorry SS this is bad, damaging to your credibility and too easily open to criticism.

It's not an equation. It's a model that very closely matches a subconscious risk assessment model that we all use. Think about it -

clear road > accelerate
road narrows > slow down
uncertain about hazards ahead > slow down
steady circumstances > steady speed

We're making these adjustments constantly to control risk based on what we know, how much space we have and how much room we need.

[safespeed]

TheExcession said:

I think there is another 'S' missing from this relationship, that being 'Skill' - what may constitute a huge risk for one driver could be quite minimal for another, though I guess this is tied in quite closely to the surprise factor.

Yes, I think 'skill' is bundled in with 'surprise'. But I'm very interested in improving Steve's model. One idea discussed elsewhere is to consider the elements that contribute to each of the three terms.

[safespeed]

7db said:

Is it really risk that you want to quantify?

Absolutely. That's the main task of driving - to keep risk at a low and acceptable level.

7db said:

Isn't it rather the speed that you are trying to figure out -- per your above post, Paul. If that is the case, what is better than being able to stop in the distance you can reasonably expect to remain clear?

No, it isn't speed, although speed is the primary risk management tool used by drivers. Steve's model underpins and explains familiar things like the safe speed rule and the Roadcraft system of car control.

Steve's model tells us (for example) that we can maintain speed while surprise is increasing if we can make more space. A practical example of this would be moving out for an obstruction or hazard ahead on the left, thereby making more space.

7db said:

The discussion then quickly focuses on what is meant by "reasonably expect", and encompasses all sorts of factors about skill, surprise, space etc etc.

Yes, and I'd be delighted if it did. But the fact remains that we couldn't drive at all if we weren't running a risk management model. Understanding how to do that well is a fundamental key to safe driving.

7db said:

You'll find speed limit advocates then arguing that above a certain speed the quality of judgement of the average motorist on their reasonable expectations isn't very good at all.

Indeed, but with poor management of space or surprise we can be deadly way below the speed limit. And of course we know that the vast majority of crashes take place well within the speed limit. But if we can help drivers to better manage risk in a general sense then we can actually improve matters.

Stick to the speed limit and you'll be safe just doesn't cut it.

[safespeed]

10 Pence Short said:

Personally I think the subject of speed is far too prominent in these discussions, when use of speed is only one aspect in what should be a whole range of motoring skills.

That's because I (and others) believe that the speed limit is now dangerously prominent in the mind of the public.

I'm sure as hell not going to sit back and watch the situation further deteriorate.

[safespeed]

vonhosen said:

Your average driver out there will be listening to the radio, having a conversation with the perosn next to them & texting someone else at the same time. It's no wonder they get surprised.

And yet they only cause one injury crash per 150 driver-years. I guess they weren't going too fast then were they? Despite the fact that >50% are still exceeding the speed limit on most road types under free flowing conditions.

Let's see - shall we base policy on less surprise or less speed? I'll give you a clue - you don't need surprise to go anywhere. (And if you demand less speed you get more surprise.)

Edited by safespeed on Monday 19th June 19:39

[safespeed]

vonhosen said:

safespeed said:

And if you demand less speed you get more surprise.

Because you divert attention to speed limit compliance
Because people believe the speed limit must be a safe speed
Because you no longer police careless driving as well as you used to
Because driver skills are acquired more slowly
Because drivers are less involved and engaged at the new lower speed
Because driver skill is relatively less valued
Because the opportunity is missed to give out worthwhile road safety messages
(off the top of my head you understand)

[safespeed]

Observer2 said:

You said it - gesture politics - because automated speed enforcement largely targets behaviour that is not unsafe. At the same time, the "unsafe" speeding events are a tiny, tiny minority of the 3.5 billion a year (as illustrated above), so the prosecution of 2.2 million is a sledgehammer.

Quite. Or rather it's worse - we're using a hammer to fix a clock... See the current front page at Safe Speed: www.safespeed.org.uk

[safespeed]

vonhosen said:

This is not just a modern thing (prosecution because of the margin over the limit), it was happening 20 years ago (& some).

But 20 years ago speed enforcement was carried out by skilled officers - not robots. In large part they used their skill and intuition to land prosecutions on the folk that deserved them. After all there were speeders everywhere. Trafpol took pride in selecting worthy targets for their efforts. I agree it wasn't perfect, but, by george, it was orders of magnitude better than we have now.

[safespeed]

7db said:

I think that it does rather depend on circs -- if you drive past a reflective yellow box at much above the speed limit, then there's something wrong with your driving.

I don't believe that's true in all circumstances. And many drivers probably pass 10,000 gatsos in a year. Do you think it's true 100.00% of the time? I don't. Probably 99% or even 95%.

Here's a case in point where I might have got caught by a gatso. I'm following a heavy looking to overtake. We round a left hand bend and I'm set up for a nearside view. No oncoming. I'm out without accelerating observing ahead. All clear. Let's go. As I near the front of the heavy in perfect safety I see a gatso on the left slightly in the undergrowth. There's nothing oncoming and I abort my overtake, braking alongside the heavy. However, if something had been oncoming, I may not have had that option and I might have been flashed.

I've gone over it again and again, and I'm certain that my observation and planning was safe. Sure the gatso was hidden behind the heavy (like the heavy was the mulberry bush) , but I'd seen the entire road, assessed the possibility of all normal overtaking risks and went for it safely.

[safespeed]

7db said:

safespeed said:

I've gone over it again and again, and I'm certain that my observation and planning was safe. Sure the gatso was hidden behind the heavy (like the heavy was the mulberry bush) , but I'd seen the entire road, assessed the possibility of all normal overtaking risks and went for it safely.

But missed the Gatso. Like a driveway, or a cyclist, or a pedestrian stepping out?

It was a totally rural location in Scotland. No buildings, let alone driveways. I'd observed the entire road and wouldn't have missed a cyclist with my nearside view. Certainly I could have missed a pedestrian in the bushes, but that sort of 'hazard' would prevent driving, let alone overtaking.

7db said:

You didn't see lines on the road when you poked out for the view?

Nope. Should looking for those be part of my observation routine?

7db said:

You looked to complete your overtake exceeding the limit? You didn't think that you could hide behind the Lorry as you went past hte Gatso...?

Not without plenty of brake, which is what happened.

Anyway, the point is that we cannot GUARANTEE 100.00% to have good prior observation of every gatso. I must say, though that the circumstances described are by far the closest I've come to being caught by a gatso.