The effects of alcohol on driving behaviours are well known and the legal limits are clear and well publicised. The consequences of drug use on driving behaviours are not as widely understood, but with recent advertising campaigns (the “wide eyed” advert) and celebrities being arrested for drug-driving, levels of publicity are increasing.

After alcohol, cannabis is the most frequently detected drug found in the blood of motorists who have been involved in a collision. In a recent journal article, Andrew Sewell and colleagues from Yale University reviewed a large number of studies examining the effects of cannabis on driving. Experimental lab-based studies have shown a wide range of impairments in driving skill after cannabis use, including reduced reaction times and psychomotor skills, and difficulties in maintaining attention and tracking objects in the environment.

Interestingly, although cannabis use clearly has a detrimental effect on driving skills, research has shown that drivers who have consumed cannabis are more cautious in their driving. A number of studies have shown that people who have used cannabis drive more slowly and leave larger gaps between their car and the car in front of them. Such findings, however, contradict the conclusions of other researchers who have suggested that individuals who use cannabis are likely to be “risk takers” and therefore are more likely to be involved in an incident.

Returning to Sewell’s review, they emphasised the dangers of driving after the consumption of both alcohol and cannabis. Each drug impairs driving skills in distinct ways. Cannabis use reduces the more “automatic” driving skills, aspects of our driving behaviour that we do not consciously put effort into, but has less of an effect on tasks that require conscious concentration and processing (such as negotiating a junction). In contrast, alcohol consumption has more of a detrimental effect on complex tasks that require conscious and focussed processing. Consequently, driving after the combined use of alcohol and cannabis has far more than just double the risk of using either drug in isolation.

Alcohol and cannabis are not the only drugs known to influence driving behaviours. There is relatively little evidence looking at the effects of cocaine use on driving skills and the research that has been done tends to suggest that the use of cocaine does not have a direct influence of driving behaviours. There are, however, indirect impairments to driving behaviour following cocaine use, due to the short term changes in temperament and long term changes in personality. The increased feelings of euphoria and invincibility that are associated with cocaine use are likely to have an indirect, but very real, influence on driving behaviours, leading to high levels of risk taking.

It is clear that the use of drugs before driving has a negative impact on driving skills, but there is relatively little publicity regarding this. For alcohol consumption there are clear guidelines regarding the number of units that may be “safely” consumed before driving. Given that drugs such as cannabis and cocaine are illegal, a “zero tolerance” approach is the only real recommendation that can be given. However, the effects of drug taking on driving should be more widely publicised and included in driving education schemes, so that individuals have a full understanding of the potentially disastrous consequences of driving after drug taking.

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Dr Victoria Bourne (BA Hons, DPhil)

Consultant to Driving Risk Management Limited

Recently there was lots of press reporting of a study conducted by the Transport Research Laboratory which looked at how listening to sport radio might influence driving behaviours. They found that reaction times were up to 20 per cent slower and last minute hard braking nearly doubled when people were listening to sport radio. Much of the media attention also emphasised the comparative similarity of the increased risk of listening to sport radio and drink driving.

We have a relatively good understanding of how mobile phone use is distracting and how this distraction impacts on our driving behaviour. Far less is known about how listening to the radio or music might affect driving. Essentially both distractions are caused by the same thing. We only have limited information processing resources. If something else, such as a mobile phone conversation or listening to sport radio, uses up some of our attention we have fewer resources available to dedicate to driving. So how much does listening to music or radio really influence our driving behaviour?

First, it’s interesting to consider why so many people listen to music or the radio whilst driving. For many people it’s a way to relieve boredom or to counteract fatigue and tiredness. One survey[1] found that 52% of respondents turn on music or the radio if they’re feeling sleepy, even though this is one of the less effective countermeasures. Drivers seem to believe that listening to music or the radio will improve driving performance, or at least avoid deterioration in performance by relieving fatigue. Unfortunately not all research supports this idea.

Much of the research looking at the consequences of listening to music or the radio has not actually aimed to examine these effects. Instead, they have been interested in the effects of mobile phone use and the music or radio condition has simply been used as a comparator task. Typically, these studies have found that having a conversation on a mobile phone[2] or even with a passenger in the car[3] causes reaction times to slow down, but that listening to music does not. It therefore seems that listening to music or the radio is at least less dangerous, or distracting, than using a mobile phone.

In car entertainment is currently diversifying and the use of televisions and DVD players for passengers in the rear of a car is becoming more and more common. Although the driver cannot see the visual display, they often can hear the audio and this may provide distraction. One study[4] compared driving behaviour whilst participants were in a driving simulator with no sound, with a radio playing or with the audio from a film in the background. As with the previous research, neither the radio nor the film audio was found to impair driving performance.

Whilst there is little evidence for audio distractions having a detrimental effect on driving behaviours, there is quite consistent evidence showing that the type of music that you listen to influences your driving behaviour. In one study[5] participants took part in a computer-based driving game whilst either listening to music that they chose or music that was chosen by the experimenter. They found that participants who were listening to their own music drove more efficiently, were less distracted and anxious and also enjoyed driving more than those listening to the music selected by the experimenter.

The emotional content of music can also influence driving behaviour. One research project[6] asked participants to listen to happy, sad or neutral music whilst driving in a simulator. They found that, in comparison to the neutral music, speed decreased when listening to either happy or sad music. However, when listening to the sad music, participants maintained good lateral control, but when listening to the happy music participants were more likely to stray out of their lane.

Relatively little research has really examined how listening to the radio or music influences your driving behaviour. Some research suggests that there are no negative consequences, whereas others suggest that what you are listening to might have either positive or negative effects. It seems likely that more research is needed to get a true understanding of the possible effects of auditory stimulation whilst driving. For example, the current evidence suggests that what you are listening to is likely to either enhance or impair your driving performance. Listening to music that you like and choose seems to be beneficial, whereas listening to a sports radio programme can have a detrimental effect, particularly if you are listening to your favourite team play.

To some extent, all possible distractions whilst driving come down to the same basic problem. Driving requires a great deal of attention and information processing, and as mentioned earlier, we only have limited resources available. Consequently, any distraction to the driver could potentially have a negative impact on their driving. Some distractions, such as the use of a mobile phone, take away more of our attention and information processing capabilities and significantly reduce the resources that can be devoted to driving.

One problem that is likely to become increasingly apparent is the number of distractions that drivers can be exposed to. If a driver is dealing with and paying attention to mobile phones, sat navs, talk radio shows and DVD players, passengers and who knows what else all at the same time, it’s obvious that their driving will be influenced. Perhaps future research needs to examine not only how individual distracters influence driving behaviour, but also the effects of multiple distracters.

[1] Anund et al. (2008)

[2] Bellinger et al (2009)

[3] Consiglio et al (2003)

[4] Hatfield and Chamberlin (2008)

[5] Cassidy and MacDonald (2009)

[6] Percher et al (2009)

Dr Victoria Bourne (BA Hons, DPhil)

Consultant to Driving Risk Management Ltd

After an accident, people often report that they failed to see the other vehicle involved in the crash with enough time to avoid the collision, even though they looked in that direction. These “looked but failed to see” errors are very common and it has been estimated that not seeing another vehicle is implicated in up to 50% of collisions. Why are we so bad at detecting other vehicles, even when we actively look for them?

Look but fail to see errors can largely be explained in terms of the way in which humans process information. Our subjective view of the world feels rather like we are watching a film and that we smoothly look around the world with a perfect representation of the outside world being efficiently processed by our brain. Surprisingly, this is very far from the truth.

When we look at something, we actually only have clear vision in a small, central part of our visual field. If you hold you thumb up in front of you at arms length, our clear patch of vision is about the size of your thumbnail. Outside of this patch our vision becomes increasingly blurry. In addition to this, the way in which we move our eyes is not at all like the smooth camera we perceive. We tend to fixate our eyes on something for around a quarter to a third of a second and then move our eyes to a new location with this movement, or saccade, taking around 30-50 milliseconds. When we are moving our eyes we are, effectively, blind.

So, our visual input is actually very degraded. Each second we will see about three “snapshots” of our visual world and these snapshots are mainly quite blurry. In reality our vision is more like a cartoon flip book where a slightly different image is shown on each page, but flipping quickly through them gives the impression that the characters are moving. In addition to being blind when our eyes move, we also have no visual input when we blink. These two factors combined mean that we are, essentially, blind nearly 20% of the time! Additionally, research has shown that drivers at a junction may only look at the road that they are merging with for less than half a second[1].

Why does it seem like we have a clear and smooth moving perception of the world, when actually we only have blurry snapshots? Essentially our brains do some amazing “piecing together” of our snapshots and allow us to perceive a clear and smooth moving world. Part of this filling in is done on the basis of our experiences and existing knowledge. Imagine driving up to a busy junction near to where you live that you cross everyday. Your memory of this junction, called a schema, is part of what allows your brain to create a complete and clear image of it. Given this it’s easy to imagine how looked but failed to see errors can occur.

The limitations of our visual processing system can explain, at least to some extent, look but failed to see errors. But other factors also contribute. How conspicuous, or noticeable, a vehicle is also makes a big difference as to whether a driver sees it or not. Much of the research in this area has concentrated on motorcycle conspicuity given the relatively high frequency with which motorcycles are not seen before a collision. Given that the front of a motorcycle is relatively small, it seems quite obvious that it would be easier to miss, but what can be done to reduce this risk.

The use of headlights and wearing of bright clothing have been examined as two of the most likely ways of making motorcyclists more visible. The use of headlights during the daytime has been found to reduce the number of motorcycle accidents; however, interestingly this is also true for cars, trucks and buses[2]. It has also been suggested that headlight use is only increases conspicuity when a motorcycle is further away and that it is little use at shorter distances[3].

Research has also examined whether there are differences in looked but failed to see errors between novice and expert drivers. Typically these studies monitor where the driver is looking and then these patterns are compared between the two groups[4]. The experienced drivers had very different looking “strategies” when driving on a motorway, urban or rural road. This suggests that they vary their driving techniques according to the environment. In contrast, novice drivers had very similar patterns of eye movements and fixations on all three of the road types. One implication of the experienced drivers being able to adopt suitable driving behaviours for different road types, this may also come at a cost. Because of all their experience, these drivers are likely to have well established schemas of the roads they frequently drive on. Consequently, they may be less likely to see and oncoming vehicle if it does not “match” with their existing schema. Ironically, this means that experienced drivers may be more likely to commit looked but failed to see errors than novice drivers.

Although looked but failed to see errors are relatively common, there are techniques that can be used to minimise these errors occurring, and consequently the associated risks. Observation is a key skill for driving, but one that is often overlooked and taken for granted. Training can improve observation skills through developing visual search strategies.  Such methods can reduce the occurrence and risks that arise due to looked but failed to see errors.

[1] Langham (1999)

[2] Olson (1989)

[3] Hole et al. (1996)

[4] Underwood

Dr Victoria Bourne  (BA Hons, DPhil)

Consultant to Driving Risk Management Limited

Driving when feeling very tired is obviously highly risky behaviour and estimates have suggested that up to 20% of collisions could, at least to some extent, be attributed to fatigue. So how does being tired influence our driving behaviours and what can we do to reduce or avoid our chances of being involved in an incident?

One of the ways in which fatigue impairs driving behaviour is by making reaction times slower. In one study[i] 240 male drivers were stopped between 1am and 6am. They were asked to rate how tired they were and to complete a simple reaction time task. Those who felt rested had reaction times of around 189 milliseconds (ms), but those who were very tired had significantly slower reaction times of 309 ms.

However, some research[ii] has suggested that this increase in reaction times might not be seen in actual driving behaviours. Instead, it is argued that, when fatigued and driving, we allocate our resources in such a way that we prioritise collision avoidance, but that other tasks, such as steering accuracy, may suffer. There is also some evidence to show that driving performance when fatigued is more affected when driving an easier route than when driving on a more complex one[iii]. It seems that the added cognitive load enables the driver to allocate their processing resources in a way that leads to safer driving behaviour.

Regardless of why fatigue influences driving behaviour, it is clear that the chances of having a crash increases greatly when the driver is tired. The important issue is how this risk can be avoided or minimised. Two psychologists, Reyner and Horne[iv], have conducted a series of experiments examining how effective various methods of reducing fatigue are.  Methods such as listening to loud music or opening the window are only effective for a very short period of time, around 15 minutes. Similarly, consuming a highly caffeinated drink only relieved sleepiness for about 30 minutes in people who had no sleep at all the night before, although it was more effective if people had at least some sleep. The researchers concluded that by far the most effective method of avoiding fatigue was to take a short nap, of just 10 to15 minutes, and then have a caffeinated drink.

Some people are more at risk of driving when fatigued than others, and those who drive as part of their occupation are particularly vulnerable. There is evidence that the attitudes of employers can influence how well drivers deal with fatigue. One piece of research[v] examined how the organisational safety climate and occupational stress might influence driving behaviours whilst fatigued. They found that fewer “near misses” occurred when drivers exhibited lower levels of work-related stress and worked for organisations with a high awareness of driver safety-related issues. However, while both factors were found to be significant and important, the occupational safety climate had a far greater effect. This study really emphasises the importance of the attitudes, policy and training provided by employers in reducing potential on-road incidents.

For instance, research has proved conclusively that there are two times of the day during which collisions due to fatigue are most likely to occur: at night time between midnight and 6 a.m. and at mid-afternoon in the post-lunch dip. A sensible risk management action would therefore be to arrange work patterns so that no business driving was required in the early hours and that drivers were mandated to take a break during the afternoon period.

Ideally, people would not drive when they feel sleepy, but in the real world this is hard to police and prevent. One thing that is clear from the research is that the risk of having a crash can be reduced if driver safety is taken seriously by both employer and employee. This involves having policies in place, procedures to identify likely risk scenarios and interventions that are tailored to specific need.

[i] Corfitsen (1999)

[ii] Van der Hulst et al. (2001)

[iii] Matthews and Desmond (2002)

[iv] Reyner and Horne (1998, 2000), Horne and Reyner (1996, 1997)

[v] Strahan et al. (2008)

• Driving Risk Management Limited can provide Fatigue Awareness Seminars for groups of up to 20 people. For more information email info@drivingriskmanagement.co.uk, call 0845 619 1275 or visit www.drivingriskmanagement.co.uk