Researchers have found no link between the number of US drivers making phone calls while on the road and the number of accidents recorded.
A team at Carnegie Mellon University and the London School of Economics analysed more than eight million incidents of car crashes and all fatalities on roads in eight US states.
They examined data before and after 9pm local time over a three-year period.
However they say their results do not include texting or internet browsing.
The timeslot was chosen because during the period studied (2002 – 2005) many American mobile phone operators offered free calls after 9pm during the week.