The Independent Police Complaints Commission (IPCC) is seeking witnesses to the collision on Monday, which resulted in a Bradford man's death.
The 34-year-old had been driving an Audi A4 in the Heaton area of the city at around 2.45am when he failed to stop for West Yorkshire Police.
He was pursued by police vehicles on the M606 before colliding with a barrier close to junction 26 of the M62 westbound.
The man, who has not been named, died at the scene.
Today the police watchdog appealed for anyone who had seen the collision and pursuit to come forward.
IPCC operations manager Ian Tolan said: “Firstly, our thoughts and sympathies are with the man’s family, and those who knew him, at this difficult time. His family is aware of our investigation and is being supported by our investigation team.
“This investigation is in its early stages and we have already started to collect and assess vital evidence in order to begin our inquiry.
"We are now appealing for anyone who witnessed any part of the pursuit to contact us to ensure we have all the available accounts.”
The IPCC said its investigators had been deployed following the collision and attended post incident procedures, where they received initial accounts from the officers involved.
The watchdog has identified a substantial amount of evidence, including the police officers’ body worn video footage, in-car footage from the police vehicles and local CCTV.
A police helicopter was also at the scene and recorded the collision with the barrier.
One witness, travelling along the motorway at the same time, has provided a statement too.
The IPCC said all the vehicles involved will be examined in due course.
Anyone with information is asked to email [email protected] or contact 0800 096 9072.