Mr Batley described how Tamzin then got out of the car before going across the northbound lane, climbing the barrier and making her way on to the southbound lane where she was struck.
“Her injuries were not survivable and Tamzin was declared deceased where she was found on the motorway,” he said.
“Police and the Independent Office for Police Conduct (IOPC) inquiries are ongoing as to the circumstances of the collision and how Tamzin came to be where she was found.”
The inquest heard Tamzin, who lived in Henlade, Somerset, was pronounced dead at 23:10 GMT and identified by fingerprint comparison.
Mr Batley said a post-mortem examination gave a provisional cause of death as head, neck and chest injuries pending further investigations.
Mrs Marsh said: “On the basis of the information provided to me, I believe I should open an inquest into the death of Tamzin Ellen Hall.”
She adjourned the case until a pre-inquest review hearing on 5 November next year, which Mrs Marsh said was the earliest available date due to the complexity of the case.
Tamzin’s family, Avon and Somerset Police, the IOPC and the driver of the vehicle which collided with Tamzin were recognised as interested people in the inquest.
The circumstances of Tamzin’s arrest and her transportation, as well as how she left the police car and what happened afterwards will also be examined.