Walnut Creek commuters heading home through the Caldecott Tunnel face overnight lane reductions starting Tuesday, Sept. 15.

Caltrans will close Bore 1, the right eastbound bore on SR-24, from 10 p.m. to 4:30 a.m. on Tuesday, Sept. 15, and Wednesday, Sept. 16, for lighting upgrades and routine maintenance, according to a Caltrans press release published Sept. 14.

All other bores will stay open in both directions during the work. Drivers should still expect delays and be prepared to merge as eastbound traffic funnels through fewer lanes.

What to expect

Changeable message signs will alert drivers approaching the tunnel. All work is weather dependent.

Caltrans advised motorists to allow extra travel time and slow down near crews in the construction zone. The agency has not published specific detour routes for this closure. Drivers who want to avoid the tunnel entirely during the 10 p.m. to 4:30 a.m. window will need to find alternate routes on their own.

Caltrans District 4 posted the advisory on X on Sept. 14, the day before the first closure night, noting that drivers should "prepare to merge & slow down for crews."

Previous Caldecott closures

The four-bore Caldecott Tunnel connects Contra Costa County to Alameda County and is the SR-24 corridor linking Walnut Creek to Oakland. Caltrans performed a similar round of overnight closures in May, when Bores 1, 2 and 3 were each shut down on separate nights from May 11 through May 13 for drainpipe sampling, water sludge collection and maintenance.

For real-time traffic updates, Caltrans directs motorists to 511.org or to call 1-800-472-7623 for statewide road conditions.