Safe Speed Forums

It seems to say that the worse your eyesight the closer you should drive.

It seems to say that the worse your eyesight the closer you should drive.

BUT if someone is already driving recklessly and too fast, then I feel the need to stop them myself. The police are NEVER around to assist.

He could have hit me, hit someone else, got out of his car and killed me.

But just moving over and letting them go isn't an actual practical solution either. I am never giving in to a bully - it's not the way I was brought up. Take 'em down, Danno.

I ALWAYS brake. That is just a classic - works stright away. My dad's in insurance and we all know anyway but he tells me deffo that if you hit a car from the rear, you pay. Do I care that when braking I could cuase a collision etc? NO. Sod you if you drive up my gate!

[engage provocative mode]
If somebody is driving 1 second behind you, surely you should be driving at a speed, at which, 1 second is an adequate stopping time! [provocative mode/]

This evening, in thick fog, a car pulled out in front of me - (not dangerously so), and set off at a brisk pace, in a 40 limit.
Trouble was he had not put any of his lights on. I flashed him, oncoming cars were flashing him, and pedestrians were turning to watch as he passed.
Finally, he indicated that he was turning right - as was I - into a 30 limit street. As we hesitated in the centre before making the turn, I hooted my horn, and flashed my lights, which he finally acknowledged by pulling over.
When I pulled along side with my window down, and yelled "You dont have any lights on mate", he waved me on, and promptly pulled out behind me, in front of a vehicle approaching him from behind, who failed to see him, as he STILL had no lights on!!

There is only so much you can do - and my worry is that it will be somebody else who dies or is injured as a result of his stupidity!

My dad's in insurance and we all know anyway but he tells me deffo that if you hit a car from the rear, you pay.

You do take things seriously here!

From: Observer
Sent: 13 December 2005 23:40
To: info@backoffplate.com
Subject: Tailgating

Dear Brian,

I was referred to your website from a post on the SafeSpeed forum.

First, I applaud your objective. I happen to think that failure to leave an adequate following distance is the single, most serious, common failure of UK drivers. Apart from the direct consequence (unable to stop in time so crashing into the vehicle ahead), I believe inadequate following distance (I avoid the word "tailgating" because the problem is much wider than the behaviour that most people would regard as "tailgating") is the direct cause of much of the congestion we see on motorways, particularly around junctions.

Having stated my support for your objective (I am undecided whether your invention is likely to be effective), I must point out what I feel is a failure in principle mentioned on your website:

"most of us are responsible drivers who have forgotten just how long the stopping distances are that we learnt years ago for our tests"

A safe following distance has very little to do with stopping distance. In general terms, the vehicle we are following will take as long to come to a halt, under emergency braking (given equal braking capacity), as us. The purpose of the safe following distance is not to provide space for braking but to provide time to react. The minimum safe following distance, in normal conditions, is two seconds. The average physical reaction time is ~0.75 seconds so a 2 seconds gap provides, in good conditions, a comfortable safety margin. The danger comes when (as I see all too often) a line of 3, 4, 5 or more vehicles proceeding with perhaps only a 1 second gap between each. Then, if the lead vehicle brakes unexpectedly, the second vehicle's safety margin is only 0.15 seconds, which is easily swallowed up be momentary inattention. The problem is multiplied for following vehicles.

I hope you see this as constructive comment.

Regards

From: Brian Clifford
To: Observer
Sent: Wednesday, December 14, 2005 8:46 PM
Subject: RE: Tailgating


Dear Tim

Many thanks for your email and the comments on the close distance driving problem.

I have to disagree with your comment on the relation between distance keeping and safe stopping distances. If I may quote you The Highway Code, p27, 105 Stopping distances. ‘The safe rule is never to get closer than the overall stopping distance’.

The Back-off Plate numbers have been calculated from these stopping distances at 70, 50 and 30mph.

The Code states that you should ‘allow at least a two-second gap… on roads carrying fast traffic.’

I personally am not happy with the two-second rule for two reasons.

1. It underestimates the safe stopping distances (SSD) at faster speeds.

At 70mph the 2-sec. distance is 61.6m SSD= 96m

At 50mph “ 44.0m SSD= 53m

At 30mph “ 26.4m SSD= 23m

2. Applying it is a distraction from the 100% concentration required in today’s traffic conditions. Very few people I know either are aware of it or use it.

A further point I should like to make concerns the distance-keeping chevrons that you may have come across on a few short stretches of the M1, M5 and M6 etc. These are spaced at 40m apart with the directive to maintain a gap of two chevrons between you and the vehicle in front. This distance is 80m and approaches the SSD of 96m and this would appear to confirm my view that the Back-off Plate distances are right.

I hope this has converted you to the cause. You will find other links to ‘tailgating’ that may be of interest at the website

www.backoffplate.com

Please let me know your reactions. I look forward to hearing from you.

Regards

Brian Clifford

Dear Brian,

Sorry it's taken me some time to get back to you. I maintain that it is wrong to think that 'following distance' corresponds (or needs to correspond) to 'stopping distance'. I acknowledge the 'rule' to that effect in the Highway Code but, useful as that publication is, it is not a driving manual. I suppose stopping distance can be seen as a guide to safe following distance, but it's not a very helpful one because it is much easier to establish with accuracy a two seconds gap than to memorise and then establish a gap of a specific size for a given speed (I acknowledge this is what your backoff plate is intended to facilitate).

I don't know whether I will persuade you but I'll have a go.

First - let me ask you to think about how you drive - and how you judge the appropriate gap to maintain from a vehicle ahead. I do not, and other drivers with whom I have discussed the question do not, think of the following gap as a stopping distance. In any reasonably likely scenario, it is not necessary for it to be a stopping distance. The vehicle we are following ('lead vehicle') cannot stop instantaneously any more than we can. It is our safety margin which allows us to time to react to the manoeuvres or actions of the lead vehicle. "Time to react" is the 'destination' ingredient of safe driving, represented by the "T" in "COAST". ("COAST" is the acronym for safe driving practice and is widely used by police and other advanced drivers. By applying Concentration, Observation and Anticipation we can create adequate Space and therefore Time to react.)

If it is correct to say that the safe following distance is intended to be the physical stopping distance, let me ask this hypothetical question: imagine you are driving (at any given speed) when the vehicle you are following at your safe stopping distance stops with no warning, for no apparent reason and absolutely instantaneously (and I mean "instantaneously" - zero braking distance). If your thesis is correct, you should be able to stop without crashing into the lead vehicle. Assume for this purpose that the Highway Code stopping distances are accurate (in fact they are materially inaccurate - for example, the quoted 70mph stopping distance is 96m of which 21m (~0.75 seconds) is 'thinking distance' (reasonable) and 75m is braking distance. The braking distance corresponds with 4.8 seconds braking time, assuming linear deceleration therefore average speed during braking of 35mph. In fact, maximum braking performance of modern cars is ~20 mph deceleration per second so braking from 70mph can be achieved in 3.5 seconds or ~55m. However, leave that to one side and assume your minimum stopping distance is actually 96m). If you have answered honestly, I think you will say that it is quite likely or very likely that you will not stop in time (I would not claim to be any different). The reality is of course that lead vehicles do not: (a) (usually) stop for no reason; and (b) stop instantaneously. However, it must follow, if the safe following distance is not providing the applicable stopping distance (and I have explained why it cannot be), then the safe following distance must be doing something else. That 'something else' is giving us time to react. For that purpose, if our physical reaction time is ~0.75 seonds, a following distance of 2 seconds allows us a reasonable 1.25 seconds additional safety margin (although more is obviously better).

One more reason - if safe following distance is supposed to represent stopping distance, it would NEVER be safe to be closer to the lead vehicle than the applicable stopping distance. Yet (for example) Roadcraft (the Police driving manual) teaches us that when preparing to overtake, we should take up an 'overtaking position' (typically ~1 second or less behind the lead vehicle). Does Roadcraft teach an unsafe practice? The answer is "No". And the reason it is not unsafe is that we can safely close the gap to the lead vehicle when preparing to overtake because we can increase our concentration, observation and anticipation to maximum level for the short period needed to prepare for the manoeuvre.

Regarding your point 2 "Applying it is a distraction from the 100% concentration required in today’s traffic conditions. Very few people I know either are aware of it or use it." - I do not think it should represent a distraction. It is easy enough to count "one one thousand, two one thousand" (or recite the old "only a fool breaks the two second rule" from the moment the lead vehicle passes a marker post or similar. I would agree that very few people are aware of the two second rule and how important it is. That is very much to be regretted. A national awareness/public information campaign of simple road safety messages (like this one) would do far more, in my opinion, to improve road safety than indiscriminate, semi-automated speed enforcement.

I hope I have given you some persuasive reasons to reconsider your view.

Regards
Tim

A further point I should like to make concerns the distance-keeping chevrons that you may have come across on a few short stretches of the M1, M5 and M6 etc. These are spaced at 40m apart with the directive to maintain a gap of two chevrons between you and the vehicle in front. This distance is 80m

At 70mph the 2-sec. distance is 61.6m SSD= 96m