Techradar can exclusively reveal the reason why you never manage to get to work on time. Drivers yakking away on their mobile phones when they should be concentrating on the road conditions are to blame.

Drivers using their mobile phones while driving are apparently impeding the traffic flow, clogging up motorways and extending commute times, according to a US survey.

When drivers are not distracted by mobile phone conversations, they are more responsive and follow traffic flows better.

"It has to do with the reaction to changes in speed," Peter Martin of the University of Utah's Traffic Lab told Reuters.

"When a driver who is not distracted is in a traffic stream and the vehicle in front slows down, the driver will brake in response. When a vehicle speeds up in front, the driver will respond and speed up," he said.

The researchers studied 36 university students, each of whom drove through six 9.2-mile long motorway scenarios in low- to high-density traffic.

The drivers used a handsfree phone during half their trips and no phone in the other half. They were told to obey posted speed limits and use turn signals but the rest of the driving decisions were up to them.

The researchers found that when the drivers were distracted by a phone conversation, they made fewer lane changes, drove slower and took longer to get where they were going. They drove about 3.2km/h slower than the undistracted drivers, and took 15 to 19 seconds longer to complete the 9.2-mile trip.

Such delays contribute to the general flow of traffic in towns and cities all across the country. Around 10 per cent of US drivers are said to be using mobile phones at any one time.

"Delays in traffic streams of very small amounts grow into massive numbers when you project it across a highway and across a nation," Martin said.

"It's a bit like breaking wind in the elevator. Everyone suffers," Martin added.

Previous studies have likened driving while talking on a mobile phone to driving after drinking alcohol. Legislation introduced last year made it illegal for UK drivers to use mobile phones without a handsfree set. Some 50 countries have also banned drivers from using handheld phones while behind the wheel.