New research reveals that talking on a hands-free phone while driving can be as distracting as talking on a handheld mobile.

The study, carried out by researchers at the University of Sussex, finds that drivers who are engaged in conversation are less likely to spot and react to hazards.

Sixty volunteers were invited to watch films shot from the point of view of a road driver and tasked with spotting road hazards such as pedestrians stepping into the road or other vehicles pulling out. The volunteers were divided into three groups. The first group was undistracted during the task whilst the other two were distracted by requests to agree or disagree with statements that required them to use mental imagery and finally statements that did not require visualisation. The volunteers were experienced drivers and not aware of the purpose of the research.

Unsurprisingly, those who were undistracted had the best hazard detection and response times whereas the worst was the group that was asked to answer questions that required visualisation. It was concluded that the worst performing group were found to restrict their gaze to a small section of the road in front of them, reducing their hazard spotting capacity.

The researchers claim that telephone conversations may affect driving performance because the two tasks compete for similar processing resources.

The road charity Brake has renewed its call for the government to restrict use of hands-free mobiles. They said the new study adds weight to extending the existing legislation to cover all mobile phone use within a vehicle, not just the use of handheld mobile devices.

In 2006, research by the National Highway Traffic Safety Administration estimated that up to 22% of crashes could be caused by driver distraction, and drivers who perform a secondary task at the wheel are up to three more times likely to have a crash.

On a separate issue, a former Navy SEAL died earlier this year after his autonomous car crashed into another vehicle in Florida. Cameras on the vehicle are believed to have failed to make a distinction between the white side of an articulated lorry and the bright sky. It did not automatically apply the brakes and crashed into the lorry as it turned left at a divided highway intersection.

Responding to the National Highway Traffic Safety Administration’s (NHTSA) decision to open a preliminary evaluation into the performance of Autopilot – Tesla’s software which controls steering, braking, lane changes and speed adjustments – during the accident, Tesla released a statement on its website.

In the Queen’s Speech in May the government announced that the Modern Transport Bill will include new laws that will make the UK ready to pioneer driverless cars.