Tunnels are regularly closed for traffic albeit for short times even if all is fine. We are not talking about extraordinary closures here. But normal maintenance closures.

What are the 10 maintenance tasks performed in tunnels?

• Testing of traffic control equipment
• Washing surveillance cameras
• Control of emergency stations
• Control of fans
• Emergency power control
• Calibration of gas meters
• Control of water supply
• Tunnel washing
• Sludge removal
• Inspection of the tunnel structure

These are the once cited at Norwegian press (I give the source below, like everybody else). Can you add more?

Cheers.

source: https://bil24.no/derfor-stenger-tunnelene-sa-ofte/