A 17-year-old girl has died after being hit by a car on the M5 shortly after being detained by police.
The incident happened between junctions 24 for Bridgwater and 25 for Taunton at about 23:00 GMT on Monday.
The teenager died at the scene and her next of kin have been informed. No-one else was injured.
Avon and Somerset Police said a mandatory referral had been made to the Independent Office for Police Conduct due to the recent prior police contact.
The M5 was closed in both directions following the crash while inquiries were carried out and repairs were made to make the motorway safe.
National Highways confirmed at 10.20 GMT on Tuesday the northbound carriageway had reopened between junctions 24 and 25, and the southbound carriageway was due to be reopened.
The site of the crash is near Creech Heathfield, close to Taunton.
There are long delays on local roads, especially the A38 near North Petherton and Bridgwater.
Motorists travelling southbound on the M5 are experiencing delays of 90 minutes, with seven miles of congestion.
There are delays of 30 minutes and congestion for two miles northbound.
Anyone who witnessed the collision or may have dashcam footage which could help the investigation is urged to contact police.
