SAN FRANCISCO (CBS SF) — Two major Bay Area tunnels used by commuters faced closures because of PG&E’s planned Public Safety Power Shutdown, but crews worked Tuesday evening to install backup generators so they stay open during Wednesday’s outage.

Caltrans said it was preparing for full closures of the Caldecott Tunnel in Contra Costa and Alameda Counties on State Route 24 and the Lantos Tunnel along State Route 1 in Pacifica due to the power shutoffs because the tunnels cannot operate without electricity.

READ MORE: UPDATE: 15 Injured, 20 Rescued After Fire Erupts Inside San Francisco Tenderloin Apartment Building

Caltrans tweeted that crews were preparing for possible full closures of both tunnels shortly after 6 p.m. Tuesday.

Caltrans said around 8 p.m. that PG&E will begin installing four backup generators inside the Caldecott Tunnel so it will not have to close. The operation will begin at 10 p.m. and could take up to 14 hours, so the Wednesday commute may still be affected, though the tunnel will remain open during the installation.

The shutdown was also thought to close the Tom Lantos Tunnels, informally known as the Devil’s Slide Tunnels, a major north-south artery that runs through the county and carries thousands of commuters every day. PG&E crews will also work through the night Tuesday to install generators to keep Devil’s Slide open during the outage.

The tunnel closures were estimated to continue for as long as five days. Changeable messages signs have been activated and will provide updated detour information as needed.

Kevin Rose, Manager of the Office of Emergency Services for San Mateo County, said he received word from PG&E that the power will be shut down in the county some time Wednesday.

READ MORE: Santa Rosa Police Search For Hit-And-Run Driver Who Critically Injured Bicyclist

ALSO READ: Bay Area Power Outage Survival Guide

“When the power is shut off, there will be no fire suppression system, so they have to shut it down,” Rose said. “Residents will have to take alternate roads to get to their destinations.”

As for the details, they were to be worked out during a conference call at 5:30 p.m. between PG&E and all the affected counties, Rose said.

Some time Tuesday, Rose said the county will alert residents through the SMC Alert system that the tunnel will close starting at noon tomorrow.

The power shutdown will affect San Mateo County residents in a way normally reserved for weather events.

MORE NEWS: Two Die In San Francisco Shootings Early Saturday Morning

“It’s like a bad winter storm without the rain,” Rose said.