Safe Speed Forums

Hmmm. That's put me on the spot! I'm trying to get hold of some real figures from current cars but the trouble is, they're so closely guarded by the manufacturers that it's fairly hopeless! The legal limit for a new car being type approved is 6.43ms^-2 with the clutch in or 5.76ms^-s with the engine connected. They refer to "mean fully-developed deceleration" in the Reg. Even then, this is only carried out from (I think!) 160kph or 80% of it's maximum speed if it can't manage 160! The term "Mean fully-developed deceleration" has a formula to define it but at a quick glance, they seem to take a "slice" of the deceleration - ignoring the first bit and the last bit (in other words, they take the "best" bit - after the brakes have warmed up but before they might be starting to fade a little)! I've been told, (by people who ought to know about this sort of thing!) that there are SOME cars out there that don't exceed the legal minimum by very much!

Now, I completely agree that most high quality performance-orientated cars will be able to VERY comfortably better this. I'm also happy to believe that there will be some road cars that can AVERAGE 0.9G from maximum speed right down to stationary, but I'm not sure that we can just let people believe that if they have a well-maintained car built in the last (say) 5 years, that they can automatically expect these levels of deceleration on demand!

As for the other caveats, I was actually thinking of making it more vague - something like "under ideal conditions, a well-maintained, good quality car on manufacturer's specification tyres and driven by an alert, skilled driver, ought to be able to ..."

How strange! I would have thought they could use it as a selling point. Performance cars could be seen as being safer Perhaps that’s a problem in today’s politically driven, road safety policy


Wow! I wouldn’t have thought that limit would be so low. Still, it’s fairly consistent with the figures given in the Highway Code.


Is this relevant? I would have thought the pads against the disks would provide more brake force than the tyre against tarmac can handle, even with cold disks or a bit of fade?
This of course assumes a good braking control system, or a driver well versed with braking control.


I can’t and won’t argue with that.

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Views expressed are personal opinions and are not necessarily shared by the Safe Speed campaign

Am I missing something…

Let’s say it takes 4 minutes for 60 cars to pass through a village all doing 30 mph. If the speed is reduced to 20 mph it will now take 6 minutes for 60 cars to pass through the village. That’s 2 minutes longer for each group of 60.

Now let’s say the morning rush/crush lasts for just an hour. At 30mph that’s 900 cars in total. By slowing the traffic to 20mph, for those same 900 cars to pass through, it equates to an extra 30 minutes of traffic. That’s half an hour more of extra smoke and noise pollution for the village!

Is that really what they want or maybe they're just too stupid to realise?

(This assumes the distance between cars is negligible at both 20mph and 30mph, which it is where I live)

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The views expressed in this post are personal opinions and do not necessarily represent the views of Safe Speed.
You will be branded a threat to society by going over a speed limit where it is safe to do so, and suffer the consequences of your actions in a way criminals do not, more so than someone who is a real threat to our society.

I think that I give more emphasis to external factors than others do. And that I am much more cautious, and forgiving, about errant behaviour on the part of non-motorist road users, especially younger ones. For example when a child runs into the road and is KSI I would start from the premise that the motorist was not showing sufficient care: the majority of posters would blame the parents for not teaching the child the GXC.

I am firmly of the opinion that, away from motorways and major trunk roads, the motorist uses the road on sufferance from the rest of the populace, human or animal. Most posters believe they use the road as of right and that non motorists should keep out of their way.

Such beliefs obviously condition ones opinion of what is a safe speed. I am far from being a slow coach and do enjoy driving quickly and do get very impatient with unnecessary slow drivering. But I am always prepared to slow down

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When I see an adult on a bicycle, I do not despair for the future of the human race. H.G. Wells
When I see a youth in a motor car I do d.c.brown

You certainly are!


Now let’s say the morning rush/crush lasts for just an hour. At 30mph that’s 900 cars in total. By slowing the traffic to 20mph, for those same 900 cars to pass through, it equates to an extra 30 minutes of traffic. That’s half an hour more of extra smoke and noise pollution for the village![/quote]

You are assuming the same linear separation between vehicles at both speeds. At 30mph the minimum safe separation is (HC stopping distance) 76feet or about 1.7 seconds. So 60 cars would pass in 107 seconds. At 20mph the safe spacing is 40 feet or about 1.3 seconds. So 60 cars would pass in 78 seconds.



If the distance between vehicles really is zero I would think that that the length of the rush hour would be vastly extended by the time it take to sort out all the rear end shunts.

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When I see an adult on a bicycle, I do not despair for the future of the human race. H.G. Wells
When I see a youth in a motor car I do d.c.brown

I didn't mean negligible as in contiguous; I meant they’re stuck up yer bum the at/from the same distance So yes, the same linear separation. It’s a rough guide/calculation, the principle holds true. Having lived in a village, Bournville, I can say they go past at the same distance whether 20 or 30mph, or more sometimes...

Sounds like you could be a cyclist as you mention them in your sig. Me too.

I think us cyclists absolutely see and suffer more than most other groups if you take into account accidents, near misses and general heart-stoppers. At least once a week, on my journey to work, something happens to me on my bike but never on my feet, never in my car and rarely on my motorbike. Why is this?

Apart from a token helmet we should wear, cyclists are basically a pedestrian but unlike pedestrians who have their own ‘road’ we are forced to mingle with the traffic. So I really can’t think of a more vulnerable or potentially dangerous means of travel myself and like I say, if you really want to see motorists, and pedestrians, at their worst – ride a bicycle.

Is say this because I hate speeding motorists nearly clipping my handlebar and the plethora of other stupid, inconsiderate and blind-sighted things I suffer from them on a regular basis. As a generalisation, I would say many drivers do go too fast too often, but that isn’t what bothers me most.

What bothers me most and what is killing and maiming most IMO is: lack of concentration, (mob phones etc.), poor judgement, and a whole gamut of other stuff besides simple speed… This focus on speed regardless of the conditions does us no favours whatsoever, but I think that's what you said or agree with

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The views expressed in this post are personal opinions and do not necessarily represent the views of Safe Speed.
You will be branded a threat to society by going over a speed limit where it is safe to do so, and suffer the consequences of your actions in a way criminals do not, more so than someone who is a real threat to our society.

i vaguely recall mean-fully-developed-decel being based on the middle 80% of the measured stop, with that decel being extrapolated forward and back to get an idealised braking distance. takes out the variability in the initiation & low speed parts of the stop.

bear in mind in this discussion 0.9g would likely be all out emergency braking, extremely uncomfortable and not something you want to be doing even due to an unexpected hazard. most people would judge 0.6 to be harsh (my own assessment).

An ex-cyclist, unfortunately, owing to ill-health. But I agree with most of your comments about the dangers of cycling. But I think the biggest danger to cyclists is not from lack of concentration but from lack of respect. Many motorists, but not I hope on this forum, consider cyclists to be a nuisance who have no right to be on the road and are fair game for aggressive behaviour to the point of killing them. This is one of the things I was referring to in the thread about attitude.

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When I see an adult on a bicycle, I do not despair for the future of the human race. H.G. Wells
When I see a youth in a motor car I do d.c.brown

I think where you are getting a little confused about rural motorways (without refering back) is a comment made by our friend weepej who said something along the lines of " no road is safe to travel after dark at more than 50MPH, if it doesn't have lighting.". I said what about rural motorways or indeed the German Auto bahn. The point being that a good rural dual carriageway can be just as safe as a rural (as in not lit) motorway at 80MPH in the dark.What is your problem with this?

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My views do not represent Safespeed but those of a driver who has driven for 39 yrs, in all conditions, at all times of the day & night on every type of road and covered well over a million miles, so knows a bit about what makes for safety on the road,what is really dangerous and needs to be observed when driving and quite frankly, the speedo is way down on my list of things to observe to negotiate Britain's roads safely, but I don't expect some fool who sits behind a desk all day to appreciate that.

I would be part of that majority if the motorist was acting in a reasonably predicable manner and the dependent wasn’t taught the GXC by their guardian – I wouldn’t automatically blame the parents (they may well have educated and tested the youngster to a reasonable level); by the same token you can’t automatically start with a premise that the motorist wasn’t showing sufficient care. Of course both these possibilities must be checked when such a KSI occurs.
I will agree we must be far less tolerant of errant behaviour from motorists than from unprotected flash-bags.


I do agree there is a level of disrespect shown to other road users and that this is wrong. I do come across the occasional twunt who shouts that roads are for cars; I usually correct them by saying ‘motorways are for motor vehicles, roads are for road users’.
IMO, most posters here don’t come across in such a selfish and ignorant manner, so I think you’ll have a job justifying that opinion, on this forum anyway.

I am firmly of the belief that the populous generally gains by the contribution from the motorist (especially cyclists, otherwise there would be no-where to cycle – or they {we} would have to pay a shedload for it). Granted there may be a few individuals who don’t benefit but you can’t keep absolutely everyone absolutely happy.


To be honest, I don’t think that actually answered my question.

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Views expressed are personal opinions and are not necessarily shared by the Safe Speed campaign

Not much. Sorry if I misunderstood you. Personally I derate my speed by about 20% when driving on Motorways at night with other traffic. The visual clues about what is going on ahead are that much harder to interpret when all you can see are lights

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When I see an adult on a bicycle, I do not despair for the future of the human race. H.G. Wells
When I see a youth in a motor car I do d.c.brown

This of course neglects the rate at which vehicles are fed into, and clear, the area (at a greater speed), and also the length of the area. Unfortunately it is this kind of oversimplification that has led to the current, failed, road safety policy. Furthermore, both these spacings are below the "two-second rule". How do you define the "safe spacing"?

I do take exception when posters, such as yourself, try to pidgeonhole me, or make assumptions about what I would consider a "safe speed". I'm sure it would surprise you to learn that I am not a speed freak, I do not drive a particularly fast or 'souped-up' car, and I have a clean driving licence and record. I know that I share these characteristics, or at very least most of them, with a significant proportion of the other regular posters here. One does not have to want to drive like a lunatic to find fault with the current, again failed, road safety policy, and improperly set limits. It is a flawed debating technique to try to paint the other party as a member of an undesirable group, indeed it is a form of ad hominem (though not nearly as distasteful as your puerile name-calling), so lets just stick to debating the issues on their merits shall we?

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Regulation without education merely creates more criminals.

graball, you were defending 80mph in the dark along "proper rural roads, not duals".

Let's ignore that the speed limit is 60mph, that is the speed at which you are legally obliged to stay under or at.



Then you say that headlights give you 75 yards forward visability.

At 80mph the stopping distance is according to Safe Speed is 109 yards, and I think that's under estimating (the reaction time is less than half of what it should be for a start).

Clearly 80 mph on dark rural single carriageway roads is way too fast, if there is something or someone in the road you are probably going to hit it, or have to take emergency evasive action (always a bad idea).



http://www.visualexpert.com/Resources/pedestrian.html

I am aware it is an oversimplification but it is no more simple than the post to which I was replying. I defined safe spacing, for this exercise, as the stopping distances given in the Highway Code. Incidentally: is the "two second rule2 in the Highway Code?


Now , where have I done that to you. I abhor pigeon-holing. Everyone is an individual not a "type". The thread trying to associate driver behaviour with type of car is, for me, completely repellent.


It doesn't surprise me at all. From reading your posts it is obvious that you are a responsible and careful person, albeit lacking in humour and been prone to take offence when none is offered


Quite agree. I have never accused anyone off wanting to drive like a lunatic.



Again: I ask when I have done that to you?


And let us not jump on the high horse when our cherished arguments are contradicted.

Despite a charming PM from PeterE expressing his appreciation of my "polite and tolerant exposition of an 'alternative' view on Safe Speed", I cannot help forming the impression that the knifes are out for anyone who dares to challenge he views of the established members.

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When I see an adult on a bicycle, I do not despair for the future of the human race. H.G. Wells
When I see a youth in a motor car I do d.c.brown

Well it was in a Porsche 911 and although I can't find any braking spec for that car, I do know that the braking distance on it is far shorter than the average car. I don't know about the safe speed table for braking distances but the Highway code chart is based on a 1960s Ford Anglia with drum brakes so is totally out of step with modern cars.

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My views do not represent Safespeed but those of a driver who has driven for 39 yrs, in all conditions, at all times of the day & night on every type of road and covered well over a million miles, so knows a bit about what makes for safety on the road,what is really dangerous and needs to be observed when driving and quite frankly, the speedo is way down on my list of things to observe to negotiate Britain's roads safely, but I don't expect some fool who sits behind a desk all day to appreciate that.

Nah! Cliamte control, MP3 stereos with Ipod docking and the like - that's what sells cars! 0.9G might mean something to techie nerds like us, but Joe punter likes a "tick list". He can understand that "having ABS" might be a good thing (even if he doesn't really know what it does) but I don't think decelerative ability will mean much. Besides, in this age, where manufacturers are increasingly removing gauges and taking the numbers off the few that remain in case they get sued when the car fails to "do what it says on the tin", they'd be daft to make numerical claims for decelerations!

Yes, it's surprising. Remember that's fully-loaded though! It just shows how good modern performance cars are! But then, that's one of the drawbacks of an over-restrictive legal framework when it comes to car design. It's no coincidence (in my view!) that some of the best engineered high performance stuff comes from a country where they have no speed limits on some roads.

I think so. The brakes need to turn the kinetic energy into heat and then dissipate it to the atmosphere as quickly as possible. You can lock the wheels pretty easily in a car with drum brakes, but you wouldn't want to stop from a "ton" in one in a hurry! Something very noticeable with "competition" pads is that they are pretty poor until they've got some heat into themselves. After that, I think they resist fade much better. The road car manufacturer needs to compromise. He needs pads with decent initial "bite" but good fade resistance. I think that as you initially stamp on the brakes, deceleration isn't that good for a second or so until the brakes warm up. I think there's then a period where they work extremely well (perhaps more than 0.9G) and then I think they start to drop off again as they get very hot towards the end of the stop. Obviously this latter effect is not really noticeable on a high quality, high performace car but there are plenty of "ordinary" cars that see a bit of a drop-off. I've just grabbed an old copy of "What Car" from July 2002 and they publish 70 - 0 stopping distances for quite a few cars that they've tested. Making the assumption that the deceleration is linear (which I don't think it will be!) most of the "premium" saloons and hatches can manage about 0.9G but there are plenty of more humble cars that post surprisingly poor figures! The worst seemed to be the WV Polo with a pretty lousy 77m stopping distance (0.66G)! Looking down the columns, about 55m from 70 is 0.9G and I have to agree that this seems like a reasonable average figure for saloons hatches and sports cars. MPVs and 4x4s are, not surprisingly, a bit worse. They record an amazing 1.2G for the Daewoo Leganza (which I'm not sure I believe!) and a rather more credible 1.06G for the Ferrari 360 Modena. The 1.2 Fiat Punto was a mere 0.7G and the 1.6 Focus a rather disappointing 0.83G along with the 1.4 Honda Civic. Not surprisingly, MPVs and 4x4s were generally worse. When you think that these figures are (presumably) recorded with an unladen vehicle (OK with a bit of test equipment) on OE tyres and brake linings, that's not all that impressive!

The 2002 copy of What Car that I referred to in the last post quotes a stopping distance of 47.7m from 70MPH for a 911 Coupe. That's not all that remarkable to be honest - not quite as good as a Laguna, for instance!! I was surprised to be honest.

Well, you absolutely will I'm afraid, whatever your motivations or intentions, it appeared belligerent and antagonistic, and I don't think that is the sort of thing we want visitors to these fora to be exposed to. So yes, for that, you have my criticism.



Contradicted, but not with any substance.



Tin-foil hat time.

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Regulation without education merely creates more criminals.

This was a 2008 911 turbo which I believe has Ceramic brakes. Top gear did a programme which featured the Mercedes Mclaren which they proved could accelerate to 60MPH and back to rest within the Highway codes stopping distance from 60MPH.

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My views do not represent Safespeed but those of a driver who has driven for 39 yrs, in all conditions, at all times of the day & night on every type of road and covered well over a million miles, so knows a bit about what makes for safety on the road,what is really dangerous and needs to be observed when driving and quite frankly, the speedo is way down on my list of things to observe to negotiate Britain's roads safely, but I don't expect some fool who sits behind a desk all day to appreciate that.

A detailed and closely reasoned argument, not. If that is your level of debate I am not surprised that you are unable to engage with my subtle reasoning and rapier like wit.

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When I see an adult on a bicycle, I do not despair for the future of the human race. H.G. Wells
When I see a youth in a motor car I do d.c.brown