A couple in Washington State has sustained multiple injuries after crashing their car into a tree while having sex, police said.

The man was drunk and the woman was sitting on top of him, engaging in sexual activity , while they navigated a local highway, State Trooper Brooke Bova told The Independent. Both were naked.

The man failed to negotiate the curves in the road, Ms Bova said, and struck a tree with his car. The woman broke her pelvis and the man broke his wrist.

Their three-month-old child, properly restrained in a carseat in the back, was uninjured.

Witnesses told police they saw the couple, both in their early twenties, exit the vehicle naked. Some witnesses reported one of them fleeing the scene. Ms Bova believes the couple were scrambling to locate their clothes before police arrived.

“I’ve never seen anything like this,” Ms Bova said.

If the man is convicted, it will be his fourth DUI in Washington State – a felony offence. He has also been charged with vehicular assault and child engagement. He was booked into Pierce County jail immediately after his release from the emergency room.

The woman has been admitted to the hospital and it is unclear whether charges will be brought against her, Ms Bova said. Authorities have not announced what will be done with the child.

A study of college students conducted by researchers at the University of South Dakota found 33 per cent of men and nine per cent of women had engaged in sexual activity while driving. None of the students surveyed had crashed their cars as a result.

Thank goodness the child is safe. All is well that ends well.