"Look where you're going"
It makes no difference to the physics or the outcome if the driver is failing to look, failing to think, failing to understand, failing to see or simply not paying attention. All the comments, descriptions and conclusions on this page are equally applicable to all these types of driver failure.
Driver inattention is a well known and widespread cause of accidents. Inattention to the road ahead takes many forms, including:
|A driver centric view
When accidents are considered, the "normal" model is to place a vehicle at some number of miles per hour, and have an object suddenly appear in front of the vehicle and ask if the vehicle could be stopped in time. This is unlike any situation which normally occurs on the road. For a start we haven't considered that the driver chose the speed on the basis of the circumstances. We've denied the driver the opportunity to anticipate the object moving into an obstructing position. And usually we've placed the obstructing object in the worst possible position, and the only possibility afforded is an emergency stop and (probably) a calculated impact speed.
We want to change all that. We want to account for the circumstances and allow our driver to set an appropriate speed. We want to give the driver the chance to observe the obstructing object and the chance to react to it. But then we want to see what happens if the driver reacts slowly or imperfectly. This is much more like a real world accident scenario. You might find the results surprising. When the driver reacts to the environment and sets a speed (as all drivers do) he has satisfied himself that if something happens ahead he can stop in time. He's probably also allowed a margin for error. This is a foundation of safe driving practice and it's the process that all drivers use consciously or unconsciously to set a speed which allows them to stop in time.
But things do go wrong. Inattention is one of the most common real failings, and may well lie at the root cause of 70 to 90% of all road accidents.
Notes to Figure 1.
Figure 1 illustrates an instant in time on a 60 mph road. The driver is looking and planning ahead, ready to deal with hazards that might appear to him in the grey hazard perception area. (Naturally the hazard perception area is illustrative, and does not relate to the mph scale.) Our driver knows that if anything appears to him in the grey hazard perception zone, he will be able to stop before he reaches it. He's even allowed for the possibility of a second of inattention, perhaps a mirror check. He knows that there are no hazards closer than 6 seconds and knows that if anything appears ahead he can stop in time. This is normal driving.
Consider the two illustrated braking options. The green area represents braking at 0.45g, which is about the max level before things become uncomfortable for passengers. In normal driving we shouldn't plan to exceed this level of braking. The red area represents what can be achieved in an emergency. Our driver keeps the difference between the two sorts of braking as a margin for error. At 60 mph the difference is about 3 seconds, and if hazard perception doesn't work, or something entirely unexpected happens emergency braking is available.
There are two areas which represent driver inaction. The first pinkish area represents inattention and the blue area represents thinking (or reaction) time.
Notice how long periods of inattention would push the braking zones well into the hazard perception zone. This is one of the main failures in driving, and it illustrates the situation where you don't see something until it's too late. Even so it would normally be possible to get some braking in before impact.
Remember we said this is an instant in time? That's very important. Suppose there is a hazard in the grey zone. It might not be serious enough to cause us to come to a full stop, but it will cause us to adjust speed. Having adjusted speed we can then stop in a shorter time, and at this new instant in time we are ready to deal with closer hazards. To understand this better, let's look briefly at an extreme example. It's a very busy situation, (imagine crowds of people, with some of them in the road) and we've slowed to just 5 mph. The same rules about safe braking zones apply, but now the distances involved are much smaller. Although we've illustrated a 60 mph situation, exactly the same shapes and layout apply to any speed. We always look ahead beyond our safe braking zone, and adjust our speed if there's a risk of our safe braking zone becoming obstructed. The speed adjustment can be all the way down to stationary if the situation demands it.
The hazard recognition zone
It stands to reason that you can't first see a road hazard 20 miles ahead, and it's obvious that recognising a road hazard when it's 1 foot ahead would lead to an "instant accident" and is a very rare occurrence indeed.
Between these extremes there's a range where all hazards must be recognised. Almost all hazards almost all of the time are recognised when they are far enough ahead that we can deal with them safely and without drama.
It's important to consider the differences between proper recognition and the failures that lead to accidents.
|Inattention and accidents
People say something happened "suddenly" and then the accident couldn't be avoided. In truth, very few things happen suddenly on the road. Much more commonly, a driver with imperfect attention will suddenly notice that something is going wrong.
|Inattention and speed
Refer to the following graph. We have calculated the equivalence between inattention and higher speed.
So, for example, a driver at 30 mph who exhibits 1.5 seconds of inattention will come to rest at the same spot in response to the same stimulus as a driver at almost 47 mph with no inattention.
We hope this demonstrates that driver inattention has a dramatic effect on safety. Quite a few reports - including the RoSPA report cited above - suggest that more than 2.5 seconds of inattention is fairly commonplace - this can produce a similar effect to driving at over 55 mph in a 30 mph zone.
Take a few seconds to be sure to understand the graph. We hear so much about the dangers of speed, yet all those claims about the supposed dangers of going a few miles per hour faster are comprehensively swamped by known and commonplace amounts of driver inattention.
You can download our "inattention / speed" spreadsheet which calculated the above graph and vary parameters to see the effects. (click here)
|Inattention and hazard perception
If a driver is late recognising a road hazard, for any reason, the effect is identical to inattention. The hazard is approached without recognition or remedial action. It makes no difference to the physics or the outcome if the driver is failing to look, failing to think, failing to understand, failing to see or simply not paying attention. All the comments, descriptions and conclusions on this page are equally applicable to all the other listed types of driver failure. We've lumped them together as "inattention" as a shorthand and because we're looking at the effects. If we were looking at the causes, then each would need to be dealt with separately.
Some things that you must do as a driver require you to take your eyes off the road ahead. One example is using the rear view mirror. So must you be at risk every time you use the mirror? The answer is no, but the correct planning must be followed.
You need a margin for error at all times
We recommend building a safety margin into your driving by only planning to use the brakes gently. If something arises within your margin, you have the option of using the brakes hard. It's very simple and it always works. See (click here).
You only look in the mirror when the situation ahead isn't developing rapidly
Obvious perhaps, but it makes a huge difference.
Managing unavoidable inattention
The very first thing we should all be doing is leaving a 2 second gap from the vehicle ahead. Contrary to common misconception, this gap has absolutely nothing to do with braking distance. We think of it as 1 second for unavoidable inattention, and 1 second for reaction. If you always have this gap, and nothing is developing ahead, you always have time for a mirror check. (Braking distance is unimportant is because the vehicle ahead has a similar braking distance to ours. The need is to start braking no later in seconds than the original gap between the vehicles.)
|Inattention and fatality
Working from the rate of emergency braking,
and also from the change in speed in a crash (known as delta v) We observe
the relationships in the following graph. (Figure 3) (the fatality risk
calculations are based on the Joksch "rule of thumb" which is discussed
Notice how rapidly the potential fatality risk falls once braking has started? After just half a second of braking from 60 mph the risk of fatality is halved. If the driver had been inattentive for just half a second, braking would not have started and the risk of fatality would be doubled.
But 1.5 seconds of inattention is commonplace (apparently). If that 1.5 seconds of inattention is combined with a need to carry out emergency braking the calculated fatality risk increases by 15 times from 6.6% to 100% of the original value.
This effect is enormous. It should be obvious that tiny changes in average driver attention would lead to quite large changes in roads fatalities.
Inattention and general risk
In this section we present the effects
of inattention at 30 mph. We have used the following parameters: Inattention
2.5 seconds, speed 30 mph, thinking time 0.75 seconds, braking effort 0.9g.
Figure 4 shows that 63% of the total distance
and 52% of the total time before coming to rest takes place while the driver
is inattentive, and over 81% of the distance is covered and 68% of the
total time before the driver reaches the brake. Notice how speed, kinetic
energy and fatality risk all remain at their maximum values during the
period before the brakes are operated. It follows that the highest dangers
are present during the period of inattention, with the risk of fatality
dropping by 50% in the first 0.25 seconds once braking actually starts.
Figure 5 is similar to figure 4 except that the horizontal scale is in distance rather than time. Both views are important, and the second appears to make our point more strongly.
However, we recommend Figure 4 as the more driver oriented view. We prefer the driver oriented view because it is the driver who made the mistake - if these sorts of dangerous mistakes are to be addressed, it's the driver who must be attending to.
We hope it's clear from these two graphs that inattention can be extremely dangerous. In fact, we would fully support a government information campaign based around the catch phrase: "Inattention kills".
Inattention - how bad is it out there?
Actually it's pretty good - we might have inattentive drivers, but don't forget we already have the safest roads in the world - so they can't be that inattentive most of the time.
We also know with certainty that the vast majority of accidents are mitigated by driver response, and logically we can't have a successful driver response without adequate attention. The following Safe Speed pages illustrate how driver responses mitigate accident effects in the real world:
(ThatAd) and (Proof):
Safe Speed pages examining the risks in pedestrian collisions.
There's no room for doubt about the evidence presented on those pages - Most of the time most drivers in most situations are effective at reducing the impact of accidents, but more importantly they avoid accidents altogether for years on end. These behaviours are largely the result of adequate driver attention.
But, on the other hand, we also know that a large number of accidents have their root cause in driver attention failings, and we should therefore deduce that any change in average driver attention should soon be reflected in the national accident statistics. So how might we alter average driver attention?
Factors affecting average attention - improving inattention
Workload - getting worse
For any activity there's an optimal workload
- too much work and we can't keep up - too little and we get bored. As
we drive faster so the workload increases. At some point we'd reach overload
and start to perform badly. But drivers have control of speed and naturally
choose to vary speed to achieve a reasonable workload in the optimal range.
If we slow them down in a misguided attempt to reduce accidents, we risk
taking their workload out of the optimal range and actually promoting inattention
and even sleepiness. The modern trend is in the wrong direction.
Distraction - getting worse
Plenty of real world driver inattention
is caused by distraction from the important tasks of driving. Distractions
might come from passengers, telephone calls, roadside billboards (to name
a few) or they might come from internal causes such as the driver worrying
about the usual things: job, relationships, money etc. If we ask drivers
to pay extra attention to something - anything - it should be obvious that
less attention will remain for the most important and immediate tasks of
driving. We believe that the modern need to pay great attention to speed
limit, numerical speed and the risk of speed enforcement is in itself an
important and significant modern distraction to the road ahead. See our
(effects) page. The modern trend is in the wrong
Concentration as a skill + Experience - not changing
We can deduce from the RoSPA figures quoted
above that improved concentration is learned as drivers gain experience.
That's another way of saying that experienced drivers have fewer bouts
of inattention. Yet we do little or nothing to help drivers to learn quickly
as they gain experience. We don't offer national additional driver training
where an instructor could point out lapses in attention and we don't even
have public information films explaining how inattention manifests itself.
It would be so easy to explain that when things appear to happen suddenly
on the road that the most common root cause is that the drivers wasn't
concentrating properly and noticed it late. There is no current trend
change - but there could be...
Safety Culture - getting worse
We've earned the safest roads in the world by having the best safety culture. If we feed the national safety culture we will help to give drivers the very best priorities and in so doing will help them to concentrate better on the things that matter the most. It follows that we must ensure we understand what the safety culture is and where it comes from - then we must nurture and develop it. Average inattention will reduce as an inevitable consequence. See (road safety). The modern trend is in the wrong direction.
|Modelling the effects of
We're working on a number of different models exploring the effects of inattention. When anything is finished and verified, we'll add it to this page. Meanwhile, if any mathematically inclined visitors are interested in collaboration on this further investigation, please get in touch. (email)
One second of inattention...
...is worth 20 mph. But safety improves remarkably quickly once braking has started.
In 2.5 seconds...
... you can reduce speed by about 50 mph if necessary. RoSPA tells us that 2.5 seconds of inattention is fairly commonplace.
When an accident risk occurs on the road at some instant an involved driver will recognise the risk. If full and complete attention is being paid then almost all risks will be recognised while they are still outside of the drivers safe braking zone.
The worse the driver's attention at the time the more likely the danger is to come within the driver's safe braking zone.
A very bad thing about inattention is that during the period of inattention the potential crash energy remains at maximum.
Sensitivity of safety to inattention
Overall road safety is very sensitive is to average driver inattention. We can't hope to eliminate inattention, but if we communicate its huge importance to drivers we can hope to make a real difference.
Modern roads policing by speed camera does nothing to promote driver attention. Instead it tends to distract drivers from the road ahead and instead requires them to pay more attention to low safety priorities like numerical speed, speed limit, speed limit compliance and the risk of speed enforcement. In this way we're moving road safety backwards, and clearly should not be surprised to see bad trends in the figures.
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SafeSpeed 2003, 2004
Created 18/11/2003. Last update 7/03/2004