The new fourth bore of the Caldecott Tunnel is expected to open Saturday, although an exact time has not been set, a Caltrans spokeswoman said Friday afternoon.
Ivy Morrison said the state fire marshal gave approval Friday to the opening, which was one of the last steps necessary.
Morrison said the opening could happen sometime Saturday morning, but not until some final striping, paving and other roadwork is completed.
Caltrans director Malcolm Dougherty made the announcement at a ribbon-cutting ceremony for the new bore in the tunnel connecting Oakland and Orinda.
State and federal transportation officials as well as local city and county leaders were on hand Friday to celebrate the long-awaited tunnel, which is expected to unclog off-peak traffic heading toward the tunnel.
"With the completion of the fourth tunnel, Bay Area residents will get to where they're going more efficiently and safely through this historically congested area," said U.S. Transportation Secretary Anthony Foxx.
The $417 million project was funded largely by federal stimulus funding as well as through revenue from Measure J, a half-cent sales tax approved by Contra Costa County voters in 2004.
Bay City News Service contributed to this report.