Driven to distraction

A study has suggested that "talking on a hands-free mobile phone while driving is more dangerous than speaking to a passenger", The Daily Telegraph reported. It said that a study of 41 motorists found that drivers talking on mobiles were more likely to drift from their lane and were four times more likely to miss their turning at the end of the journey.

This study has some limitations that make its findings difficult to interpret and to come to any conclusions about road safety. However, the message is an important one: drivers should avoid distractions while driving.

Where did the story come from?

Dr Frank A Drews, Monisha Pasupathi and David L Strayer from the University of Utah carried out this research. There is no indication that external funding was received for this study. The study was published in the peer-reviewed medical journal: the American Psychological Association.

What kind of scientific study was this?

In this experimental, observational study, the researchers wanted to compare the impact of mobile phone use and passenger conversations on driving performance. Their aim was to investigate if a conversation between the driver and a passenger speaking directly to each other in the car was different to that being had by the driver talking on a mobile phone. The researchers' theory was that passengers in cars would know what demands driving were placing on the driver and adjust their conversation accordingly (such as reducing the need for the driver to respond).

The researchers used 48 pairs of adults consisting of two friends aged between 18 and 49 years of age.

One person from each pair was randomly picked to be the driver in a driving simulation. This simulated a 24-mile journey in conditions that required them to pay close attention to surrounding traffic. All the drivers and passengers were told that after driving for eight miles, they were to leave the highway and pull into a rest stop.

Each driver did the simulated drive without holding a conversation. This was used as a baseline measure to assess each driver’s performance when there were no distractions.

The other person in the pair was then assigned either to be a passenger (sitting in the simulator with the driver) or a friend on a hands-free mobile phone. One person in each pair was then randomly chosen to lead the conversation (the speaker) and the other person was told to mostly listen. The speaker was instructed to tell a story about a time when their life had been threatened (not previously known to their friend). The researchers believed that this type of ‘close call’ story would be engaging among friends.

Various aspects of driving performance (operational, tactical and strategic) were measured using car position, speed and distance from the car in front. Driving performance was measured first for each driver without any distractions and then when they were conversing with their partner in the car or on the phone.

The difference in driving performance was used to compare the effects of mobile phone calls and conversations with a passenger. Those conversations were also transcribed and coded and any references to traffic by either the driver or the passenger were noted.

What were the results of the study?

Data was only available for 41 of the 48 pairs of adults due to some technical problems.

The researchers found that drivers showed a greater tendency to drift left or right during phone conversations compared to conversations with a passenger. Having a passenger or not made no difference to the speed of the driver.

Drivers talking on mobile phones kept a greater distance between them and the car in front compared to drivers with a passenger.

Drivers in the phone group were four times more likely to fail the driving task (i.e. miss the exit to the rest stop) than those in the passenger conversation group. Overall, there were fewer references to the traffic in phone conversations than passenger conversations and these additional references were made by the passenger rather than the driver.

What interpretations did the researchers draw from these results?

The researchers conclude that compared to driving without distractions, talking on a mobile phone negatively impacts lane keeping, increases the headway (i.e. distance between car in front), and impairs navigation. A conversation with a passenger does not have this effect.

What does the NHS Knowledge Service make of this study?

The results from this small experimental study are difficult to interpret. While drivers on mobile phones had a worse lane position and were less able to navigate than drivers with passengers, they drove with a greater (and therefore safer) distance to the car in front.

The researchers chose to analyse their data using a simple statistical test. This test is limited in that it cannot take into account other factors that could have affected driving, such as age or the nature of the relationship with the partner. These may have been responsible for the small differences between the drivers using phones and those talking to a passenger.

The implications of these results for driving safety are not clear. However, using mobile phones while driving is dangerous and, in general, drivers should avoid distractions when they drive.

Sir Muir Gray adds...

As a reformed user, I think others should act on these findings.