What Makes Some Drivers Speed?

Reasons as to why some drivers tend to exceed speed limits constantly and why some are prone to drunk driving are entirely different, a study by UT researchers suggests.

A study commissioned by the Estonian Road Administration and carried out by a team of researchers led by Jaanus Harro, UT Professor of Psychophysiology, sheds light on biological factors behind risky traffic behaviours such as speeding and drunk driving.

According to Diva Eensoo, a member of the team and research fellow in healthcare management at the UT Department of Public Health, drunk drivers and speeders exhibit two entirely different types of impulsive behaviour.

Causes are found in the brain

In both cases the underlying causes can be attributed to the person’s impulsivity and tendency to seek excitement. However, whereas a drunk person decides to sit behind the steering wheel without considering the potential consequences of his or her actions, speeders tend to be very aware of what they are doing.

Individuals who are prone to drunk driving find it hard to restrain themselves and yield easily to their impulses. Their behaviour is inconsiderate, with rash decisions that lead to risky situations. “Such persons act with no regard for themselves or others,” says Eensoo.

Drivers who speed are also impulsive and feel a constant need for novel sensations and experiences, but at the same time they are characterised by quick decision-making and an optimistic disposition. They are conscious of the risks they are taking and therefore feel that there’s nothing wrong with exceeding the speed limit.

According to Eensoo, risky behaviours have a clear biological background. Their causes lie in the levels of serotonin, a hormone produced in the brain. The functioning of serotonin neurons can be measured by studying platelet monoamine oxidase (MAO) activity in blood samples. Among drunk drivers platelet MAO activity was found to be considerably lower than in the reference group, whereas in highway speeders it turned out to be higher.

“However, biology doesn’t determine everything – the influence of the surrounding environment needs also to be factored in,” says Eensoo.

Predicting and correcting drunk driving

In conducting the study blood samples were collected from 1866 students participating in driving courses at driving schools in Tallinn and Tartu. They were also invited to fill out questionnaires in order to establish their personality traits.

All participants were given feedback on their susceptibility to either conscious (speeding) or unperceived risk-taking behaviours (drunk driving). Half of those who had exhibited a tendency towards risk-taking behaviours also attended a lecture on typical high-risk situations that may occur in traffic, as well as drivers’ behaviours in them, and were offered advice on how to keep one’s impulses in check.

A year later, researchers consulted the traffic violation database to see how these beginning motorists had behaved in traffic over the past year. It turned out that among those who had attended the risk avoidance training there were 50 percent less detected instances of speeding than in the reference group which had not received the training. Exactly the same proportions held true for those with a record of drunk driving.

Eensoo stresses that despite the limited scope of the study it is clear that identifying risky drivers at driving schools by means of personality tests and blood samples and offering them special training courses yields positive results.

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