Noah Berger for The Bay Citizen

A catwalk rises over the new East span of the Bay Bridge on Monday, Aug. 29, 2011, in San Francisco

Drivers heading to San Francisco over the President's Day weekend won't be able to use the Bay Bridge. Caltrans announced Tuesday that it will close the upper deck from 8 p.m. on Friday, Feb. 17 until 5 a.m. on Tuesday, Feb. 21 for construction work on the new eastern span.

The lower deck, which carries traffic from San Francisco to the East Bay, will remain open throughout the closure.

In a statement, Caltrans said crews will be building "a slight detour near the toll plaza" that will allow the new eastbound lanes of the span to be completed earlier than originally planned.

The bridge's current westbound lanes stand in the path of where the new span's eastbound lanes will be. The detour will "slightly" shift westbound traffic to the south of its existing path, and will make room for construction crews to demolish sections of the existing roadway that are in the path of the new incline section. A video explanation of the new configuration is available at www.baybridgeinfo.org.

Without the detour, Caltrans said, the new span's eastbound lanes would not be finished until the spring of 2014, six months after the westbound lanes. The detour should allow the new span to open to traffic in both directions in the fall of 2013.

To help prevent freeway gridlock, BART will be running hourly trains to 14 stations all night on the Friday, Saturday and Sunday of President's Day weekend.

The service is a rare exception to BART's long-standing policy of not running trains overnight, despite the pleas of bar and theater patrons. BART maintains it needs the early-morning hours to perform maintenance on the tracks that cannot be done while trains are running.

BART spokesman Jim Allison explained Tuesday that the transit agency is able to run overnight service — but only for a limited time before track problems pile up.

“During the Loma Prieta earthquake, we ran overnight transit for a month, but then we had to catch up with all the maintenance,” Allison said.

The nearly 25,000 fans of the Facebook page Make BART Trains run 24 Hours shouldn’t get their hopes up that overnight train service will become a regular thing.

BART has given up on the idea, board member Bob Franklin told The Bay Citizen last week. Instead, the transit agency is looking into an all-night bus that would cross the bay and stop at select BART stations.

Caltrans warned drivers that the work on President's Day weekend may cause traffic on other Bay Area bridges. The agency also said inclement weather could cancel the bridge closure.

Caltrans said that when the upper deck reopens on Tuesday, Feb. 21, it may take drivers some time to adjust to the detour. A similar detour installed over Memorial Day weekend last year also caused some traffic delays, while drivers adjusted to the new eastbound traffic lane configuration.