Safe Speed Forums

I'm sorry Noob Saibot, you are completely wrong.

If your above statement were true, motorways would be the most dangerous of all our roads. They are NOT. They are the safest, despite traffic speeds of 70mph or above.

Roads with the fastest traffic speeds are in fact the safest. Not the most dangerous.

To attempt to over-simplify road safety is a dangerous issue, slower speeds do not necessarily equate to a reduced frequency of collisions, or reduced severity.

I'm not sure what you mean by "brake assist" in this context? I'm thinking of the system that some manufacturers fit which decides whether or not you are applying the brakes in a "panic" situation. If (it thinks) you are, the computers take over and do nothing but try to make each wheel give you as much retardation as possible.

As for wet stopping distances, I'm curious as to what you base this assertion on? Sports car manufacturers (and drivers) generally spend more on tyres than the lower end of the market for cost reasons. I accept that in the special case of braking hard from high speed in standing water, there is more chance of the lighter car with the wider tyres aquaplaning but in our hypothetical debate we'd already loaded them up to the same weight. The sports car's biggest advantage is a low centre of gravity so you don't get the weight transfer off the back wheels on to the fronts which means the back brakes are free to do more to help stop the car. In an MPV, I doubt the back brakes would be doing very much at all by the time you get to a (say) 0.8G stop!

T2006, that's why I qualified what I said with 'all other things being equal'.
Yes there are many, many other factors at play, road type / conditions being one, but I don't see how you can wriggle out of the basic facts, without resorting to some highly convoluted arguments. Are you saying the roads would be safer if we all drove faster?

We can both agree there but I'd add tyres to the list too. The complications arise when designing the rest of the car to optimise the tyres' grip so that it can generate the heat in the discs in the first place. that bring suspension gemoetry, damper characteristics, weight distribution and heaven only knows what else into the equation! The important thing is to convert all the KE into heat AND THEN GET RID OF THE HEAT - that's what sports cars tend to excel at but the bits you need to do that are too expensive for small hatchbacks.

I was thinking about brake servos, otherwise known as power assisted brakes, and ABS in particular. These things are sometimes sacrificed in sportier cars as they have less weight to brake and these things are heavy (TVR, for example, do not put ABS on IIRC?)

I'm not sure about those things you described - I don't think I would like to hand over control of braking to a mechanical device.

Arguably the BEST* thing to come out of motorsport is the improvements in things like brakes that filter down to "mere mortal" cars, my car now has vented discs and it's only a short while ago that these were for exotic cars only!

(* and the thrill of driving on the edge on a track!)

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the brake booster (i assume we are referring to) is a completely independant system (at present, in most cases, subject to change) from the ABS.

boosters sit between the pedal and the master cylinder and amplify your pedal input (usually) using engine vacuum, and as such is a passive system.

ABS of course sits between the master cylinder and the wheels to prevent wheel locking.

Probably not but we're not saying everyone should drive faster rather everyone should find the safespeed for the conditions.
The roads would certainly become unnecessarily more dangerous if we're forced (by menaces or otherwise) to drive slower.

Let's face it, our speed camera policy makes the other things quite unequal.

Nope. Even with the qualification (in fact entirely because of the qualification) your statement is wrong.

As was pointed out in an earlier post - all things being equal (two identical cars carrying identical weights begin their journey from the same point at the same time, both accelarate at the same rate but one settles at a speed 10 MPH higher than the other...) there is every possibility that the faster moving car passed the point where the hazard occurred well in advance of it happening and therefor avoided the collision completely, whereas the slower vehicle got there just at the right time to smack into it.

You generalisation is fundamentally incorrect. You may have to redefine your point but as it stands it is nonsense.

You'll struggle to find any car (except maybe the odd kit car) these days without a servo. In any case, servos don't make the car stop any better or worse - just make the pedal easier to push. People often get in my car and comment on how lousy the brakes are. They're not to be honest, it's just that it doesn't have as much servo assistance as most modern cars but it stops plenty well enough if you press the pedal hard enough. To be honest, I think most modern cars are grossly over-servoed.

As for "brake Assist, nobody likes admiting that a machine can do it better than they can but manufacturers only started fitting it because it was painfully obvious that most people (OK, "many" people) could NOT do it as well as the computer!

ABS isn't that heavy in the great scheme of things. TVR are pretty much unique amongst their peers for not fitting ABS but that was a reflection of the last chairman's personal feelings on the matter rather tha na weight-saving measure. To my mind, they got it wrong there but that's just my opinion! I've a feeling the situation might change under the new guy!

Or the faster car could arrive just in time, and have less time to react, whereas the slower car hadn't got there yet? As I said in my original post, time and place arguments completely fudge the issue and bear no relation to the overall risk.

By all means argue against speed camera policy where you believe it to be failing, but you should not need to rely on denial of basic physics to do this.

I'm not wriggling out of anything.

I was just informing you, your prevoius claim was completely incorrect.

No convoluted arguement is necessary to disprove your claim as my previous post demonstrated very well.

Oh, and I did not suggest the roads would be safer if we all drove faster. I just suggested the likelihood of crashing was not increased by speed, as motorways being the safest roads prooves.

It has been demonstrated that drivers, driving at the 85-90th speed are at lowest risk of crash. This is a well known scientific fact, freely available in the public domain.

So, in some circumstanses, if condtions permit and a driver is driving below the 85-90th percentile speed..... YES - it would be safer to speed up rather than slow down.

Drivers driving below 85th percentile speed are at dramatically INCREASED risk of crash. So driving slowly can Kill.

I've already mentioned, you should not attept to oversimplify road safety. It is not as black-and-white a relationship as you suggest.

I'll give you a different answer. I don't see how speed can ever be different if all other things are equal. After all drivers select speeds to suit environments so either the driver has to change or the environment has to change. That's the only way to get different speeds.

Now if the environment changes and speeds increase we know that crash likelihood drops. Faster road are safer. There's an interesting conflict between this observation and traffic calming of course.

But what about drivers? Can we make them drive more slowly without changing their psychology? I don't think so.

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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

That's not really how it works. The 85th percentile drivers tend to not crash because they are competent but not over confident. It's the quality of the driver that gives the speed choice and the crash risk. So a less competent 50th percentile driver would not be improved if we forced him to drive faster.

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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

Both of the above statements ae utterly wrong. The studies show that the safest (least crash involved) drivers choose to drive at speeds in the 80-90%ile range. It DOES NOT FOLLOW that it is safer to drive in the 80-90%ile speed range. That just happens to be the range of speeds chosen by the safest drivers. We do not want to encourage drivers whose level of comfort/competence leads them to drive at (say) the median speed to think they will be safer if they drive faster. THE OPPOSITE IS TRUE

It is also totally untrue to say that crash risk increases dramatically below 85%ile speed. The crash risk doesn't change. However, some of the least safe drivers (most crash involved) are those driving at well below 85%ile speeds (not just a bit below, well below). On the other hand, it follows that they will crash at low(er) speeds so they may represent less of a danger to others than (some) drivers who drive well above the 85%ile speed.

SNAP

It doesn't improve overall understanding or advance our cause if we respond to an absurd argument with an equally absurd counter-argument.

You're both missing the point. In the real world, the environment is always different, and all things are never equal.
Theories which depend on everything else being equal, when they never, or seldom, are in the real world, can't apply to the real world - no matter how sound the maths and physics are on paper, if it can't, or doesn't, happen in the real world then it doesn't work.
I have been writing 'real-world' computer simulations for the best part of two decades now, not only concerning road safety but in many other fields as well. In my experience, the results of real-world simulations are pretty close to what's actually measured in real-life, but those of theoretical, 'all other things being equal' models seldom come close, and are generally way out.



Less time than what? That's another theory which looks good on paper, but doesn't match up to what happens in the real world.



Far from fudging the issue, they explain (or come close to explaining) what actually happens. Simple 'all other things being equal' models simply don't.



Then so be it. There was a time when people were put to death for daring to suggest that the earth is not the centre of the universe.

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

Sorry if my previous post had a degree of ambiguity to it.

The point i was attemting to make is that often that many drivers are forced to drive at a speed well below the 85th %ile speed due to poorly set, council imposed speed limits.

Thus reducing a drivers speed does not necessarily equate to reduced risk accidents.

Pete, help me out here because I've never really been able to connect with the supposed point being made in this observation.
If something happens to which we have to react as we are travelling along, then I can see that its true to say that if we'd been travelling at a different speed we'd not have been in the vicinity when that particular thing did happen.
However, we may have well arrived been in the vicinity of something else happening either earlier or later in our journey and thus we might still have to react as before.
Life isn't like a video game in which we watch the pattern of falling rocks or knife-thowing ninjas and move to avoid them. Every time we undertake a similar journey, all the probability numbers are re-crunched and one day, at one particular time the die might be cast such as to place the guy with the Walkman on his ears waving goodbye to his mate as he steps off the pavement from behind a van, right in our path at precisley the point where our speed would make a difference to our ability to avoid killing him.
Isn't this the point being made in those, if you brake from 40/30/20 adverts?

Yes, it could happen, but what's the probability? Think of how often you have to brake hard, or take other action, to avoid an accident. How often does it happen, on average? I'll hazard a guess that it's not less than about once a year, tops - so to say that it's extremely unlikely that anything's going to happen on the same journey is a vast overstatement.



Yes, that does happen - when a myriad of circumstances come together and places you precisely at the wrong place at the wrong time. But your speed is just one of those many circumstances and so has little say in it - it could be 10mph or 100mph.
But, of course, being a good driver, you will have seen the parked van from some way off, you will have considered the possibility of someone stepping out from behind it, and so you will have slowed right down in good time before you passed the van just in case there was someone there about to step into your path.

And - more to the point - being a good, attentive, hazard-aware driver, the slower your normal travelling speed the longer you spend on the road, so the higher the probability is that you're going to be in the wrong place at the wrong time.



No, the point of those ads is to make us believe that we automatically change from good, safe drivers to rabid child-killers the moment we drift slightly above the speed limit, and to try to make us grateful for the good people in the SCP's for keeping us safe.

Those ads typically rely heavily on the 'all else being equal' theories, which tell us little or nothing about what really happens in the real world.

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