Motorway 'safe' distance chevrons
Discussion
WinstonWolf said:
You would be better off asking a policeman.
Do you think we should all be maintaining a 215 metre gap at 70MPH? That allows for a traffic density of less than fifteen vehicles per KM on a three lane road if all vehicles are travelling at the legal limit.
I see the problem now, you have a specific scenario in mind where this would not be appropriate. Without actually telling us this you just state that following with a gap larger than 2 seconds is always wrong. Do you think we should all be maintaining a 215 metre gap at 70MPH? That allows for a traffic density of less than fifteen vehicles per KM on a three lane road if all vehicles are travelling at the legal limit.
So let's turn this around and add traffic density into the discussion.
109er said:
Talking of 'gaps' between vehicles, why is it if you leave a safe gap you always get some idiot who
must pull/go into it reducing your safety margin
PS I own an old Land Rover with a basic single circuit braking system with 11" drum brakes
109er, you have my sympathy, you don't 'drive' a 109 you 'helm' it!must pull/go into it reducing your safety margin
PS I own an old Land Rover with a basic single circuit braking system with 11" drum brakes
Edited by 109er on Monday 13th January 14:41
Part of the logic of the large following gap is that it is there for someone to get into either in an emergency avoidance situation, or simply by accelerating into the gap, it's there for my safety and that of others.
Good, now I have the figure roughly in metres of 7 seconds at 70mph. I knew all along of course...
So with a gap of 215 metres between the car in front and myself I have the official stopping distance at 70 mph as per the Highway Code in which to stop, should the vehicle in front hit something solid, such as the car whose differential has seized in lane 3 due to the lack of proper servicing intervals being adhered to.
Someone said I'd attract attention from the bobbies? Really? They're going to be feeling pretty silly when I ask them why it is wrong to maintain the correct stopping distance behind the nearest hazard, don't you think? Also when I state that I am able to stop in the distance I can see to be clear. And what's going to happen? I'm getting done for Dangerous driving or Due care or something? And people have said that I must be the nutter here.
I'm so glad I didn't put my life in the hands of the driver ahead, following 2 seconds behind him at 70mph, trusting that he has done proper servicing and his vehicle is in good working order and his standard of driving and concentration is up to the mark, what if he's not looking ahead at the danger that is unfolding as a bad change in position forces someone into his path causing him to brake heavily, he may not be very mirror conscious to boot, and has no idea how close I'm following, the consequences don't bear thinking about.
The majority of posts in this thread only underline what I'm saying, that I would be foolish to trust YOU with MY safety. It isn't going to happen, when I see drivers following with woefully inadequate following distance, as I often do, I'm the first to drop out, it's never long until I can drop back in and get my gap sorted again, only difference is that I'm now well away from the muppets who feel 2 seconds is adequate at 70, 2 seconds to me is adequate at 30.
I'd like to see a TrafPol's response to what I've said here, for your benefit not my own, I already know what the response will be.
Being tailgated is never an issue because when you leave a sensible gap the vehicle behind you tends to leave a similar gap and so on...
So with a gap of 215 metres between the car in front and myself I have the official stopping distance at 70 mph as per the Highway Code in which to stop, should the vehicle in front hit something solid, such as the car whose differential has seized in lane 3 due to the lack of proper servicing intervals being adhered to.
Someone said I'd attract attention from the bobbies? Really? They're going to be feeling pretty silly when I ask them why it is wrong to maintain the correct stopping distance behind the nearest hazard, don't you think? Also when I state that I am able to stop in the distance I can see to be clear. And what's going to happen? I'm getting done for Dangerous driving or Due care or something? And people have said that I must be the nutter here.
I'm so glad I didn't put my life in the hands of the driver ahead, following 2 seconds behind him at 70mph, trusting that he has done proper servicing and his vehicle is in good working order and his standard of driving and concentration is up to the mark, what if he's not looking ahead at the danger that is unfolding as a bad change in position forces someone into his path causing him to brake heavily, he may not be very mirror conscious to boot, and has no idea how close I'm following, the consequences don't bear thinking about.
The majority of posts in this thread only underline what I'm saying, that I would be foolish to trust YOU with MY safety. It isn't going to happen, when I see drivers following with woefully inadequate following distance, as I often do, I'm the first to drop out, it's never long until I can drop back in and get my gap sorted again, only difference is that I'm now well away from the muppets who feel 2 seconds is adequate at 70, 2 seconds to me is adequate at 30.
I'd like to see a TrafPol's response to what I've said here, for your benefit not my own, I already know what the response will be.
Being tailgated is never an issue because when you leave a sensible gap the vehicle behind you tends to leave a similar gap and so on...
WinstonWolf said:
You would be better off asking a policeman.
I don't need to, I stated earlier in this thread that I have done this with a Class 1 Police advanced in the passenger seat.WinstonWolf said:
Do you think we should all be maintaining a 215 metre gap at 70MPH?
In a word Yes! WinstonWolf said:
That allows for a traffic density of less than fifteen vehicles per KM on a three lane road if all vehicles are travelling at the legal limit.
And?25NAD90TUL said:
Good, now I have the figure roughly in metres of 7 seconds at 70mph. I knew all along of course...
So with a gap of 215 metres between the car in front and myself I have the official stopping distance at 70 mph as per the Highway Code in which to stop, should the vehicle in front hit something solid, such as the car whose differential has seized in lane 3 due to the lack of proper servicing intervals being adhered to.
Someone said I'd attract attention from the bobbies? Really? They're going to be feeling pretty silly when I ask them why it is wrong to maintain the correct stopping distance behind the nearest hazard, don't you think? Also when I state that I am able to stop in the distance I can see to be clear. And what's going to happen? I'm getting done for Dangerous driving or Due care or something? And people have said that I must be the nutter here.
I'm so glad I didn't put my life in the hands of the driver ahead, following 2 seconds behind him at 70mph, trusting that he has done proper servicing and his vehicle is in good working order and his standard of driving and concentration is up to the mark, what if he's not looking ahead at the danger that is unfolding as a bad change in position forces someone into his path causing him to brake heavily, he may not be very mirror conscious to boot, and has no idea how close I'm following, the consequences don't bear thinking about.
The majority of posts in this thread only underline what I'm saying, that I would be foolish to trust YOU with MY safety. It isn't going to happen, when I see drivers following with woefully inadequate following distance, as I often do, I'm the first to drop out, it's never long until I can drop back in and get my gap sorted again, only difference is that I'm now well away from the muppets who feel 2 seconds is adequate at 70, 2 seconds to me is adequate at 30.
I'd like to see a TrafPol's response to what I've said here, for your benefit not my own, I already know what the response will be.
Being tailgated is never an issue because when you leave a sensible gap the vehicle behind you tends to leave a similar gap and so on...
If the diff of the vehicle in front seizes will it stop instantly?So with a gap of 215 metres between the car in front and myself I have the official stopping distance at 70 mph as per the Highway Code in which to stop, should the vehicle in front hit something solid, such as the car whose differential has seized in lane 3 due to the lack of proper servicing intervals being adhered to.
Someone said I'd attract attention from the bobbies? Really? They're going to be feeling pretty silly when I ask them why it is wrong to maintain the correct stopping distance behind the nearest hazard, don't you think? Also when I state that I am able to stop in the distance I can see to be clear. And what's going to happen? I'm getting done for Dangerous driving or Due care or something? And people have said that I must be the nutter here.
I'm so glad I didn't put my life in the hands of the driver ahead, following 2 seconds behind him at 70mph, trusting that he has done proper servicing and his vehicle is in good working order and his standard of driving and concentration is up to the mark, what if he's not looking ahead at the danger that is unfolding as a bad change in position forces someone into his path causing him to brake heavily, he may not be very mirror conscious to boot, and has no idea how close I'm following, the consequences don't bear thinking about.
The majority of posts in this thread only underline what I'm saying, that I would be foolish to trust YOU with MY safety. It isn't going to happen, when I see drivers following with woefully inadequate following distance, as I often do, I'm the first to drop out, it's never long until I can drop back in and get my gap sorted again, only difference is that I'm now well away from the muppets who feel 2 seconds is adequate at 70, 2 seconds to me is adequate at 30.
I'd like to see a TrafPol's response to what I've said here, for your benefit not my own, I already know what the response will be.
Being tailgated is never an issue because when you leave a sensible gap the vehicle behind you tends to leave a similar gap and so on...
25NAD90TUL said:
WinstonWolf said:
If the diff of the vehicle in front seizes will it stop instantly?
Is that a serious question?Yes, with a loud bang, it may skid for a couple of metres but it won't be many, it certainly won't be in a position to coast safely to the hard shoulder, coasting will be out of the question. Any movement will be out of the question, unless of course you hit it.
Probably... if it is then someone clearly doesn't understand coefficients of friction and the time and distance required to stop, even when a mechanical problem might stop the drivetrain from rotating.
FWIW, in ten years of investigating RTAs I saw precisely one occasion where a differential had seized (mainly due to a parts monkey specifying the wrong final drive ratio on a replacement). You won't be surprised to hear that given the size of the tiny pinions inside the differential, the inertia of the 4x4 simply sheared the pinion gears apart.
My boss saw something similar ten years before that where a milk float went overspeed (40 mph or so downhill) and the input shaft and motor locked. The differential worked perfectly - spinning one rear wheel up to 60 whilst slowing the other wheel down to 20. Float slews across road and crash happened. In neither case did the vehicle miraculously stop its forward motion. Nothing short of hitting an immovable part of the scenery or a vehicle coming the other way will do that.
FWIW, in ten years of investigating RTAs I saw precisely one occasion where a differential had seized (mainly due to a parts monkey specifying the wrong final drive ratio on a replacement). You won't be surprised to hear that given the size of the tiny pinions inside the differential, the inertia of the 4x4 simply sheared the pinion gears apart.
My boss saw something similar ten years before that where a milk float went overspeed (40 mph or so downhill) and the input shaft and motor locked. The differential worked perfectly - spinning one rear wheel up to 60 whilst slowing the other wheel down to 20. Float slews across road and crash happened. In neither case did the vehicle miraculously stop its forward motion. Nothing short of hitting an immovable part of the scenery or a vehicle coming the other way will do that.
25NAD90TUL said:
25NAD90TUL said:
WinstonWolf said:
If the diff of the vehicle in front seizes will it stop instantly?
Is that a serious question?Yes, with a loud bang, it may skid for a couple of metres but it won't be many, it certainly won't be in a position to coast safely to the hard shoulder, coasting will be out of the question. Any movement will be out of the question, unless of course you hit it.
WinstonWolf said:
Two metres? Is that a serious answer?
I didn't say 'two' I said 'couple', could be a 'few' metres, either way it isn't going to be many is the crucial thing. It could be any solid object or semi-solid, or not even solid at all, just an 'object' whether technically solid or not, if you hit it, you have a problem.When a differential goes bang, in the vast majority of cases the drivetrain will seize solid in a fraction of a second, it's going to take a powerful winch just to drag it onto a lowloader.
25NAD90TUL said:
So with a gap of 215 metres between the car in front and myself I have the official stopping distance at 70 mph as per the Highway Code in which to stop, should the vehicle in front hit something solid, such as the car whose differential has seized in lane 3 due to the lack of proper servicing intervals being adhered to.
You have more than twice the Highway Code stopping distance. Can one take conservatism too far in these things? Or on the other hand, why only leave twice the HC distance when you could, to be on the even safer side, leave four times?The vehicle ahead can only stop instantly if, as you say, it hits something solid (not sure a single vehicle, seized diff or otherwise, counts). Personally, I don't follow as far back as HC stopping distances as a matter of course as I can generally see that there isn't anything solid ahead of the vehicle in front. If I do spot something ahead, e.g. stationary traffic, I will probably open the gap up to rather more than 2 seconds.
Edited by SK425 on Monday 13th January 16:33
StressedDave said:
Probably... if it is then someone clearly doesn't understand coefficients of friction and the time and distance required to stop, even when a mechanical problem might stop the drivetrain from rotating.
FWIW, in ten years of investigating RTAs I saw precisely one occasion where a differential had seized (mainly due to a parts monkey specifying the wrong final drive ratio on a replacement). You won't be surprised to hear that given the size of the tiny pinions inside the differential, the inertia of the 4x4 simply sheared the pinion gears apart.
My boss saw something similar ten years before that where a milk float went overspeed (40 mph or so downhill) and the input shaft and motor locked. The differential worked perfectly - spinning one rear wheel up to 60 whilst slowing the other wheel down to 20. Float slews across road and crash happened. In neither case did the vehicle miraculously stop its forward motion. Nothing short of hitting an immovable part of the scenery or a vehicle coming the other way will do that.
It's ok splitting hairs like that, it detracts from the point though, it doesn't matter to me technically what it is they hit, or how unmovable it is, I'm trying to illustrate the point that an emergency is what it says, it happens suddenly, the more breathing space you have the better your chances of avoiding it. In your example the pinions sheared you say, that isn't the same as a differential locking up, as you are aware.FWIW, in ten years of investigating RTAs I saw precisely one occasion where a differential had seized (mainly due to a parts monkey specifying the wrong final drive ratio on a replacement). You won't be surprised to hear that given the size of the tiny pinions inside the differential, the inertia of the 4x4 simply sheared the pinion gears apart.
My boss saw something similar ten years before that where a milk float went overspeed (40 mph or so downhill) and the input shaft and motor locked. The differential worked perfectly - spinning one rear wheel up to 60 whilst slowing the other wheel down to 20. Float slews across road and crash happened. In neither case did the vehicle miraculously stop its forward motion. Nothing short of hitting an immovable part of the scenery or a vehicle coming the other way will do that.
25NAD90TUL said:
WinstonWolf said:
If the diff of the vehicle in front seizes will it stop instantly?
Is that a serious question?Lorries losing treads and loads also springs to mind.
I also tend to leave a larger gap if following a cluster of cars with very small gaps, the car in front of you will decelerate much quicker if it hits the car in front of it. Granted you should have seen this happening, however there is still the matter of debris and the gap behind to allow for.
If nothing else a larger gap means you can help smooth out braking waves thus contributing to the overall throughput.
25NAD90TUL said:
WinstonWolf said:
Two metres? Is that a serious answer?
I didn't say 'two' I said 'couple', could be a 'few' metres, either way it isn't going to be many is the crucial thing. It could be any solid object or semi-solid, or not even solid at all, just an 'object' whether technically solid or not, if you hit it, you have a problem.When a differential goes bang, in the vast majority of cases the drivetrain will seize solid in a fraction of a second, it's going to take a powerful winch just to drag it onto a lowloader.
A couple is generally recognised as two, hair splitting aside it will not stop any quicker than the manufacturer's published stopping distance.
StressedDave said:
You won't be surprised to hear that given the size of the tiny pinions inside the differential, the inertia of the 4x4 simply sheared the pinion gears apart.
Whenever I see the splines on driveshafts and such like, it always amazes me that those tiny little jiggers are what push the whole car along. I know there's gearing and all that, but even so, they're so ickle!WinstonWolf said:
It will lose speed in a slightly greater distance/time than if the driver mashed the pedal to the floor and left it there.
hair splitting aside it will not stop any quicker than the manufacturer's published stopping distance.
Put it this way it won't be a planned, controlled stop.hair splitting aside it will not stop any quicker than the manufacturer's published stopping distance.
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