Lancashire Police has suspended a driver training technique which has been blamed for causing a pile-up on the M61 on Wednesday.
Two lanes were closed for two-and-a-half hours and tailbacks stretched back to Manchester after five police cars crashed near Chorley.
The experienced traffic officers had been attempting a "controlled stop" on an unmarked target vehicle.
Five officers were taken to hospital with whiplash injuries.
Assistant Chief Constable Adrian McAllister said he had ordered an investigation, adding: "Thankfully, none of my officers has been badly injured and no members of the public were involved at all.
"In the circumstances I feel it only right that the constabulary suspend this type of training with immediate effect, pending the outcome of the investigation and a full report to the Chief Constable."
The force said the training had been supervised by advanced driving instructors with warning signs used to keep normal motorists away.
The incident at junction nine resulted in the closure of two lanes of the motorway while the wreckage was cleared.