The George Massey Tunnel will be closed in both directions for four consecutive nights later this week.
The Ministry of Transportation and Infrastructure said in a statement that overnight closures of the tunnel, which connects the cities of Delta and Richmond on Highway 99, are needed as part of the ongoing upgrades to the counterflow system.
The tunnel will be closed on the following dates and times:
Thursday, April 4 and Friday, April 5
Saturday, April 6 and Sunday, April 7
The ministry says drivers can detour via the Alex Fraser Bridge during the overnight closures. Emergency vehicles and late-night buses will be able to travel through the tunnel with the help of an escort vehicle.
The upgraded electronic lane-control system is expected to be in operation in time for the morning commute on April 8, according to the ministry, marking the end of the manual counterflow controls that have been used during the upgrades.
Counterflow lanes are used on weekdays to allow three lanes of traffic to flow northbound toward Vancouver during the morning rush hour, switching to southbound during the afternoon commute.
An estimated 80,000 vehicles use the four-lane tunnel daily, leaving it congested for hours.
The NDP government has committed to building a new $4.15-billion eight-lane tunnel to replace the crossing by 2030.