The Clyde Tunnel was shut to traffic last night while emergency services carried out a major training exercise.
The exercise on the M8 involved the Clyde Tunnel - which links Govan to Whiteinch in Glasgow.
The incident involved police, firefighters and ambulance crews.
Drivers were urged to seek alternative routes, but the tunnel was open as usual this morning after the exercise was completed by 10pm yesterday.
A spokesman from Police Scotland said: “This live play exercise is an integral and important part of our training.
“It has not impacted the local communities or any of the services involved.”