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