How distracting is talking on a mobile phone when driving?

It’s well known that we’re not supposed to drive while using a hand-held mobile phone to talk or send an SMS, but you can drive while talking on a hands free kit. If you want to know how difficult it is to drive while texting, have a go at this game by NZTA. But what about driving using a hands-free phone (either via Bluetooth, plugged directly into your car or via a headset or headphones attached to your phone)? Is it any different than talking to someone else in the car?

A recent study at the University of Illinois and the Beckman Institute has evaluated how distracted we are in four different situations:

Driving without anyone talking to us
Driving while talking to someone in the passenger seat
Driving while talking to someone on a cellphone where the other person can’t see what you are doing
Driving while talking to someone on a cellphone where the other person can see where you are driving on a small screen

It turns out that what the other person can see profoundly affects your likelihood of having an accident. Previous studies have found that, contrary to what you might think, passengers often aren’t distracting (as long as you’re not having an argument with them). If they are also drivers they act like another set of experienced eyes on the road and can alert to driver to potential issues and dangers.

The experiment involved setting up a number of fairly novice drivers (almost all college students) in a simulator. They had to complete a quite complicated drive which involved navigating in traffic where the roads and other drivers were unpredictable. The team monitored all aspects of the driver’s performance including reaction times, lane position, following distance, speed, ability to navigate to a specific destination, and so on. Their speech to their conversation partner was recorded, too, and an eye tracker was used to track exactly what they were looking at.

The results were interesting. The first scenario – a driver with no distractions – had the least risk of having an accident (which is not surprising as the driver could pay full attention to the road). The second scenario – having a passenger in the front seat sitting next to them – did increase the accident rate slightly, but the passengers did function as an extra set of eyes, helped with navigation and remembered road signs. The third scenario was like a typical phone call – the conversation partner could not see what the driver was doing. This tripled the likelihood of a collision. However, in the fourth scenario where the conversation partner had a video feed to a small screen so that they could see what the driver was doing, the accident risk was reduced by 40-50% over scenario three, but was still higher than with a passenger in the car.

As the conversations were recorded, too, it was noticed that when the conversation partner could see a developing danger, they tended to adjust their conversation, either stopping talking, or providing assistance or additional warning about the road ahead.

What wasn’t covered in the study was how much the risk increases when having a heated or emotional conversation rather than a non-emotional conversation; whether a call to discuss what to have for dinner is less risky than a call with bad news.

What it did prove though, was that it is much more risky to talk to a person on the phone while driving, whether they can see what you are doing or not, and therefore it’s best just to let them leave a message rather than answer it.

The reasons for the increase in accident risk are that when your brain is focused on the conversation, your reaction times are much slower – an average of 9% slower according to some studies.