Motorway 'safe' distance chevrons

[25NAD90TUL]

WinstonWolf said:

I think this is the point we've all been putting across

Only point I've seen is that two seconds is enough, see my recent post on this.

[25NAD90TUL]

WinstonWolf said:

If it is woefully inadequate why does a H&S obsessed government advise it?

Winston, surely you're not suggesting the government can offer any kind of enlightened view on any subject let alone driving? Look at the recent flooding and the responses from the 'floods' minister, laughable! How well the flood defence system has worked, yeah right, only in areas not prone to flooding! It's not rocket science, get the drain channels and rivers dredged, oh dear no money for that...

Government is a joke on every level especially road safety, look at their belief in reducing speed limits against driver further education.

I took your comment above as the joke it was intended as.

Mate if that is so who on earth are the DoT who I quoted their Highway Code book? Department of Transport, hang on, that IS the government!

[WinstonWolf]

25NAD90TUL said:

I also spoke to a Police Advanced friend who said he considered a minimum of '30 feet at 30mph and an extra yard for every extra mile per hour. At 70mph 30 feet plus forty yards, giving a safe minimum following distance of 150 feet'.

So while I accept, and never disputed, that my 7 seconds is more than double what is considered the minimum, this information also points to your 2 seconds at 70 as WOEFULLY INADEQUATE which, if you remember was what I said originally.

Now if anyone wants to dispute that then good luck to 'em.

Right, time for the physics again

150 feet is a bit over 45 metres...

So, we know that 1MPH = .44M/s (excuse the metric)

Which means that at 70 MPH you're travelling at 30.8 M/s



So in two seconds you'll travel 61.6 metres or 202 feet which gives you an additional 25% safety margin on the distance your police AD advised.


Now not only do I dispute it, I've used your own numbers to punt you into the back of the net

[WinstonWolf]

Oh, and I used to be HRG, here's me playing with my brakes

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

[25NAD90TUL]

WinstonWolf said:

Right, time for the physics again

150 feet is a bit over 45 metres...

So, we know that 1MPH = .44M/s (excuse the metric)

Which means that at 70 MPH you're travelling at 30.8 M/s



So in two seconds you'll travel 61.6 metres or 202 feet which gives you an additional 25% safety margin on the distance your police AD advised.


Now not only do I dispute it, I've used your own numbers to punt you into the back of the net

Bullst! You haven't, my post stated that 2 seconds at 70 was 62 metres, you could've saved yourself those maths if you had only read it properly! Yes the TrafPol did say his figures were an absolute minimum. Presumably that figure was meant for Police Advanced Drivers perhaps.

PMSL at you, but it's all good, enjoying your input good buddy!

[WinstonWolf]

25NAD90TUL said:

WinstonWolf said:

Right, time for the physics again

150 feet is a bit over 45 metres...

So, we know that 1MPH = .44M/s (excuse the metric)

Which means that at 70 MPH you're travelling at 30.8 M/s



So in two seconds you'll travel 61.6 metres or 202 feet which gives you an additional 25% safety margin on the distance your police AD advised.


Now not only do I dispute it, I've used your own numbers to punt you into the back of the net

Bullst! You haven't, my post stated that 2 seconds at 70 was 62 metres, you could've saved yourself those maths if you had only read it properly! Yes the TrafPol did say his figures were an absolute minimum. Presumably that figure was meant for Police Advanced Drivers perhaps.

PMSL at you, but it's all good, enjoying your input good buddy!

That's not maths, see the post I popped in above this one if you want maths

[25NAD90TUL]

WinstonWolf said:

That's not maths, see the post I popped in above this one if you want maths

No! I don't need a maths lesson ta, I'm a Doctor in an advanced discipline of Environmental Science!

My post had that inclusion, the 62 metres thing, yes it was more than the police figure, and your point is?

My point is that two seconds is not enough, see the 'deluded' part of the quote. Not quite getting your point buddy. Are we going off-topic in order to attempt to save face?

Edited by 25NAD90TUL on Saturday 18th January 23:50

[25NAD90TUL]

WinstonWolf said:

Oh, and I used to be HRG, here's me playing with my brakes

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

Oh, for a minute I thought that HRG was an abbreviation for something important.

Good stuff though, I love maths also! I have a BSc, MSc and Phd, not in Maths but Maths applied to a branch of Environmental Science. I have a brass name plaque although it isn't mounted at my front door. I worked as a consultant for English Nature before they changed to Natural England, I rarely use the pre-fix, unless I want to lord it over someone lower down the academic scale than myself. Here I'm just the Separation_Master a well known, much misunderstood character with a penchant for the stylistic side of the system.

Good to make your acquaintance buddy, we're never going to agree I can see that, but no matter, it's all good, enjoying our intercourse.

Edited by 25NAD90TUL on Sunday 19th January 05:05

[WinstonWolf]

25NAD90TUL said:

WinstonWolf said:

That's not maths, see the post I popped in above this one if you want maths

No! I don't need a maths lesson ta, I'm a Doctor in an advanced discipline of Environmental Physics!

My post had that inclusion, the 62 metres thing, yes it was more than the police figure, and your point is?

My point is that two seconds is not enough, see the 'deluded' part of the quote. Not quite getting your point buddy. Are we going off-topic in order to attempt to save face?

Not at all, check out my brake maths post

Nothing will stop dead on the motorway. Nothing, nada, zilch. You merely need to match the slowing rate of the vehicle in front within the two seconds and you will stop clear of the obstruction.

I do enjoy a bit of robust debate

[Tonsko]

[SK425]

25NAD90TUL said:

The two seconds rule is considered a BARE MINIMUM and you're deluded if you think it's enough.

Why would it be considered a minimum if it was not considered enough? That would be a non sequitur of the sort only blurted out by the deluded.

[SVS]

WinstonWolf said:

Nothing will stop dead on the motorway.

I was once driving briskly in the outside lane of the M25 when the engine fell out of my car. The car stopped dead. I hadn't braked, of course, so there were no brake lights to alert the driver behind me.

Unusually for the M25, the driver behind had left a good stopping distance in front of him. He was just able to manage an emergency stop.

I later found out that my engine bolts had failed at once. It was a freak accident, but freak accidents can and do happen occasionally. That's when you need an emergency stop. The added danger of a freak accident is that it increases your 'thinking distance' and therefore lengthens your total braking distance, because your brain isn't prepped to respond to the unusual. Your brain is prepped to look for what it expects to see. This is a well established phenomenon called 'inattentional blindness'.

'Thinking distance' alone has been found to be up to 2 seconds (!) in these circumstances

Edited by SVS on Wednesday 15th January 03:25

[25NAD90TUL]

SK425 said:

25NAD90TUL said:

The two seconds rule is considered a BARE MINIMUM and you're deluded if you think it's enough.

Why would it be considered a minimum if it was not considered enough? That would be a non sequitur of the sort only blurted out by the deluded.

Hi, the 'deluded' thing came from a passage I quoted earlier from some advanced driving literature. Please don't dissect my post in order to remove the comment from the context in which it was delivered.

[StressedDave]

SVS said:

'Thinking distance' alone has been found to be up to 2 seconds (!) in these circumstances

Indeed - the typical reaction time quoted from the literature (found from some relatively scary tests undertaken by the Merkins) is 0.75 to 1.5 seconds, so allowing 2 seconds makes sense. Back in the day anyone requiring more than two seconds to react to something was entering the envelope where charging for WDC/WRC/DDD would be considered.

Now my maths suggests that the stopping time (and FWIW, we never, ever, use time in such calculations in an accident investigation sense because nobody cares how long it took you to hit someone, only whether you could have avoided it geographically), allowing for a 2 second reaction time, is 6.5 seconds. Now, having a second second distance gap might make sense if your method of reaction is to wait for everyone else to come to rest before braking.

Otherwise, it is excessive. This doesn't make a difference if you're sitting in lane 1 and everyone can overtake you, but doing the same in lane 3, and the methods employed to maintain said gap might be considered unreasonable to the drivers behind. Whilst I would never compromise safety, forefront in my mind as an advanced driver is how my actions will be perceived and I'd imagine continually dropping back (as it might be perceived) would cause a smidgin of red mist to may drivers on the road.

[25NAD90TUL]

StressedDave said:

Now my maths suggests that the stopping time (and FWIW, we never, ever, use time in such calculations in an accident investigation sense because nobody cares how long it took you to hit someone, only whether you could have avoided it geographically), allowing for a 2 second reaction time, is 6.5 seconds.

So half a second short of the 7 seconds I've been banging on about?

[Vipers]

SVS said:

WinstonWolf said:

Nothing will stop dead on the motorway.

I was once driving briskly in the outside lane of the M25 when the engine fell out of my car. The car stopped dead. I hadn't braked, of course, so there were no brake lights to alert the driver behind me.

Unusually for the M25, the driver behind had left a good stopping distance in front of him. He was just able to manage an emergency stop.

I later found out that my engine bolts had failed at once. It was a freak accident, but freak accidents can and do happen occasionally. That's when you need an emergency stop. The added danger of a freak accident is that it increases your 'thinking distance' and therefore lengthens your total braking distance, because your brain isn't prepped to respond to the unusual. Your brain is prepped to look for what it expects to see. This is a well established phenomenon called 'inattentional blindness'.

'Thinking distance' alone has been found to be up to 2 seconds (!) in these circumstances

Edited by SVS on Wednesday 15th January 03:25

Bloody ell, st does happen. But I did have a chuckle at your term "The car stopped dead"........

The entire debate is good, some good points, but why do they only have chevrons on only a couple of roads, and with the brain dead morons we all meet daily are probably a waste of paint. What I can't stand are the morons who insist driving 25mm in front of you.

[StressedDave]

25NAD90TUL said:

So half a second short of the 7 seconds I've been banging on about?

The bit in brackets is actually the more important bit. A 7 second gap equates to a smidgin over 219m. Allowing for a 2 second reaction time (generous), the total stopping distance from 70 mph is a smidgin under 134m. Any more reaction time is treading in the realms of carelessness, so you're wasting 85m of road unnecessarily.

Stop getting hooked up on time - it's the wrong approach. No one cares how long it takes to get to a point on the road. They do care that if they're stationary at that point, you'll not hit them.

[bomma220]

Mate of mine was driving his '96 Micra on the M1 at about 3am. He was overtaken by a DB9 just before entering a

chevron section of the motorway. He did his very best to obey the 2 chevron rule but completely buggered his car

up in doing so...

[25NAD90TUL]

StressedDave said:

The bit in brackets is actually the more important bit. A 7 second gap equates to a smidgin over 219m. Allowing for a 2 second reaction time (generous), the total stopping distance from 70 mph is a smidgin under 134m. Any more reaction time is treading in the realms of carelessness, so you're wasting 85m of road unnecessarily.

Stop getting hooked up on time - it's the wrong approach. No one cares how long it takes to get to a point on the road. They do care that if they're stationary at that point, you'll not hit them.

Forgive me because I'm getting confused, to me it looks like you are saying 6.5 seconds required to stop and in the next breath you state a distance which doesn't equate to 6.5 seconds in terms of distance travelled at 70, I realise that upon applying the brakes you will be decelerating hard from 70 downwards, so won't be doing 70 for the whole 6.5 seconds.

Not being dis-respectful or arguing for the sake of it, I need clarification on this, so you are saying that what I quoted from the Highway Code is not correct in your view and the full stopping distance recommended in the book as the safe following distance is not what you are recommending I use as a minimum?

My reaction times aren't too bad, but I don't want to start relying on them for my survival, in case they are not as good as I imagine. Finally do you consider a following distance of two seconds at 70mph to be adequate?

Edited to add: The bracketed part of your post? Seconds/metres it amounts to the same distance, to me the seconds thing is just a good way of measuring the distance while driving, seconds/metres surely that is just splitting hairs...

Everything I have ever done, read, been taught, used on test is being thrown into disrepute here, it looks to me as though even the Highway Code's advice is being cancelled out, this what get's me about AD, so much conflicting stuff, Christ I have a mate who's a bobby who regularly accompanies me and who considers my thinking sound, how many mway patrols I must have passed when using a 7 second gap, or 215 metres if you prefer that nomenclature must I have passed in my career doesn't bear thinking about and never once been pulled or even had a sideways glance.

Best wishes Dave and seriously I'm not messing about here or bickering for the sake of it, this to me is a serious safety issue we're discussing.

Edited by 25NAD90TUL on Wednesday 15th January 09:25

[0000]

25NAD90TUL said:

So half a second short of the 7 seconds I've been banging on about?

No.

You've been talking about 7 seconds gap at 70mph, not 7 seconds at, say, an average of 35mph (not accounting for reaction time and assuming linear deceleration).