A 17-year-old girl who died after being hit by a car on the M5 had got out of a police vehicle shortly before the crash.
The collision involving the teenager and a car happened around 11pm on Monday, Avon and Somerset Police said. The girl died at the scene.
The force has referred itself to the Independent Office for Police Conduct (IOPC) due to prior police contact.
The teenager was being transported to custody in a police vehicle and had got out of the car shortly before the collision, the IOPC said in a statement.
Police said the victim’s next of kin had been notified and are being supported by a specially-trained officer.
No one else was injured in the incident.
An IOPC spokesperson said: “We have started an investigation into the circumstances surrounding the death of a 17-year-old girl who was struck by a vehicle on the M5 near Taunton last night (Monday).
“We were advised by Avon and Somerset Police that the girl was being transported to custody in a police vehicle and had got out of the vehicle shortly before the collision.
“We sent our investigators to the police post incident procedure to begin gathering evidence.
“Our sympathies are with the girl’s loved ones and everyone affected by her death.”
Nationals Highways confirmed that the motorway reopened in both directions shortly after 11am on Tuesday.
Anyone who witnessed the crash or has dashcam footage is urged to call 101 and give the call handler the reference of log number 1170 of 11 November.
Detective Chief Superintendent Rachel Shields said: “Our thoughts are first and foremost with the girl’s family.
“Overnight we have updated her next of kin regarding what has happened and we will ensure they are supported by specially-trained officers at what is an incredibly difficult time following the tragic loss of such a young life.”
She added: “The IOPC has decided to take on the investigation independently, and we welcome the oversight it will give.
“We recognise this incident has had a significant effect on the devastated officers, plus members of the public, who witnessed what happened, as well as other officers and staff involved in our response. We will ensure staff are able to access any welfare support they may benefit from following this tragedy.”
