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Ten seconds to impact.

An experimental way to view driving as a continuous process of accident avoidance. 

This page is a worthy illustration of broad concept only. Don't take the view precisely.

 
Introduction

When you drive a car you are continuously varying course and speed to avoid road risks. If you shut your eyes and let go of the wheel, you would be extremely likely to crash within about ten seconds. It's when this continuous process of accident avoidance has a failure that we have a crash. Almost all accidents on UK roads could have been avoided if either party took positive action in the last couple of seconds before the crash.

What we want to do here is to introduce the important idea of a continuous scale from safe driving to fatal crash. It's a young idea, and not published elsewhere as far as we know, but it's a view that tends to provide insight into how accidents happen and how they might be avoided. It points at failures in driver planning that could not possibly be overcome by the likes of speed enforcement. Especially we want you to think in terms of driving as a continuous state of crash avoidance.

We certainly don't claim that the idea is fully developed. There might be different and more useful ways to express it, and there might be other parameters that should be introduced to develop full understanding. The most controversial aspect is the link to accident and injury figures. We're not seriously suggesting that at 0 seconds to impact everyone will be killed. But we are suggesting that larger failures from drivers do more damage and cause more injury.

Do not take the "seconds" scale as precise or even literal, it's merely a general guide. For some accident scenarios, especially those at high speed the seconds figure will be about right. In town, where speeds are lower and hazard density is greater, the real seconds scale would be compressed.


 

Ten seconds to impact: Table of Effects

Seconds
to impact
Example description
[we could add descriptions of steering to avoid accidents, and add other scenarios, but these examples should illustrate the point.]
Consequence
10 No obstructions or hazards anywhere to be seen (or to hide). We accelerate. -
9 No obstructions or hazards ahead. We accelerate. -
8 Hazards ahead, but so far away that we need take no action. We maintain speed. -
7 Hazards ahead, but a minor alteration to course or speed will render them safe. We probably lift off. -
6 Obstruction ahead, but gentle braking will stop us in time to avoid an impact. Does anyone think we should guess that this happens 3,000,000,000 times each year on UK roads? It probably does.
5 Obstruction ahead, but firm braking will stop us in time to avoid an impact. 300,000,000 cases of late hazard assessment (total guess work)
4 Obstruction ahead, but emergency braking will stop us in time to avoid an impact. 30,000,000 cases of emergency braking (educated guess work)
3 Insufficient time remains to take avoiding action and damage results. 3,000,000 damage only accidents annually in the UK
2 Far too little time is available to avoid the impact. 300,000 slightly injured annually in the UK
1 We brake, but far too late and crash hard. 35,000 seriously injured annually in the UK
0 Immediate crash at significant speed 3,400 fatal accidents annually in the UK

 
Conclusions and discussion

We think the concept of a continuous scale with degrees of failure leading to degrees of consequences is a vital and enlightening view of driving. You might say "accidents aren't so special"; they are just the more extreme forms of minor errors. Good driving is made of observation, anticipation and planning. These skills, when used properly, can keep all of us at the higher end of the scale. 

In normal driving we wouldn't expect to get closer than 6 seconds, with cases of 5 seconds happening perhaps a few times each year for experienced drivers. Advanced drivers would always consider "emergency braking" at the 4 second level to be a serious error. If you want to avoid accidents, it would make sense to learn sufficient anticipation to avoid ever going worse than 5 seconds. 

Other ways to describe the scale would be in terms of hazard proximity, danger proximity, immediate risk, or degree of driver failure. Doubtless all are equally valid, and we were tempted to add descriptive columns. Since none of the views is more true or less true we settled on the simplest.

You might agree that there's little difference between the nature of the failures at the 5 seconds level and the nature of the failures at the 0 seconds level. Since vast numbers of drivers never normally get closer than 6 seconds, yet exceed the speed limits regularly, this is yet more evidence that speed is likely to have a very small role to play in the serious consequences at 0, 1 and 2 seconds.

It's most interesting that the numbers in the conclusions column rise with a log scale (1, 10, 100, 1000...) This indicates that each degree of failure is ten times less likely than the previous degree. The top four numbers are official figures, but at higher numbers of seconds we've inserted illustrative guessed figures which we think are reasonable.

Summary points:

  • Normal driving is a continuous state of crash avoidance.
  • Crashes happen when the crash avoidance systems fail but the scale is continuous.
  • Failures of the driver's crash avoidance systems are rare. The steepness of the (logarithmic) slope is absolutely astonishing.
  • Failing to recognise a hazard soon enough is the primary failure that leads to crashes, and that too is subject to the same steep slope. Bad failures are extremely rare events.
  • The major controlling parameter in crash severity (or avoidance) is obviously the time at which the hazard is recognised. Recognise the hazard in good time and nothing happens. Recognise it too late and people die. 
  • It follows that when accidents occur the speed at impact is far more a function of the time when the hazard was recognised than it is a function of the previous free travelling speed.
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Created December 2002. Last update 7/03/2004
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