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States should ban all driver use of mobile phones and portable electronic devices, except in emergencies, a US safety board has said.

The National Transportation Safety Board (NTSB) recommendation includes a ban on hands-free devices, making it stricter than any current state laws.

Thirty-five states have banned texting when driving, and nine states have outlawed hand-held mobile phone use.

But enforcement is generally not a priority.

And no states ban the use of hands-free devices for all drivers.

The NTSB does not have the power to impose such a nationwide ban, but its recommendations carry significant weight with federal regulators and lawmakers.

In a unanimous vote, the board also recommended increased enforcement of existing laws.

would make an exception for devices seen as aiding driver safety, such as GPS systems.

The debate was prompted by a pile-up in the state of Missouri last year, caused by a 19-year-old driver who sent or received 11 texts in the few minutes before the crash.

Missouri has a law banning drivers under 21 years old from texting while driving, but was not enforcing it regularly at the time of the accident.

"We're not here to win a popularity contest," NTSB chairman Deborah Hersman told reporters on Tuesday.

"No email, no text, no update, no call is worth a human life."

Other high-profile cases investigated by the NTSB include the death of 25 people in a train collision, which involved an engineer texting.

Another accident involved a lorry driver who was using his phone when he collided with a van, killing 11 people.

About two out of 10 drivers have texted or emailed from a mobile phone while driving, according to a survey of US drivers by the National Highway Traffic Safety Administration.

Half of drivers between 21-24 years of age had done so.

The survey found that many drivers do not think it is dangerous when they use phones on the road - only when others do.