The Malahat will be fully closed nightly into the weekend to allow crews to make repairs in the area damaged by rain and flooding.
On Tuesday, the highway will close at 7 p.m., reopening at 6 a.m. Wednesday. From Wednesday to Sunday, it will be closed 6 p.m. to 6 a.m.
Single-lane alternating traffic will continue at other times.
The Ministry of Transportation opened the Malahat to single-lane alternating traffic on Tuesday morning, with vehicles moving in 30-minute increments.
Emcon Services, which provides maintenance on southern Vancouver Island roads and highways, said the decision was made after completion of a geotechnical assessment of the affected area after heavy rainfall.
Significant delays are expected.
Drive B.C. says the highway will be open in 30-minute intervals and is recommending essential travel only.
The Malahat closure was put in place Monday afternoon between West Shore Parkway and South Shawnigan Lake Road.
Finlayson Arm Road is not being used as a detour route.
B.C. Ferries ran the ferry between Brentwood Bay and Mill Bay through the night after the road closure led to increased traffic on the route.
The corporation said Tuesday that traffic remains high on the route. The M.V. Klitsa has returned to its regular posted schedule.