Police, fire and ambulance crews from Gloucestershire are to be tested with a mock exercise which will replicate a major motorway crash.
Emergency staff will practise extracting people from crashes and treating their injuries afterwards.
Jon Hall, from Gloucestershire Fire Service, said they dealt with "hundreds of smaller collisions" but wanted to test how they handled big incidents.
"We are constantly striving to improve our response," he said.
The training exercise will take place in Avonmouth near Bristol.