ORINDA, Calif. -- Federal, state and local officials gathered in Orinda Friday to celebrate the beginning of construction on the fourth bore of the Caldecott Tunnel.

Rep. John Garamendi, D-Walnut Creek, joined members of the U.S. Department of Transportation, the state Legislature, Caltrans, and local transportation agencies at the groundbreaking ceremony for the project that will add a fourth bore to the tunnel connecting Oakland and Contra Costa County via state Highway 24.

The four-year project, which costs $420 million, will alleviate traffic congestion in the area and is expected to create jobs for more than 5,000 construction workers.

John Porcari, deputy secretary of the U.S. Department of Transportation, said the money "is being invested in more than just a tunnel."

The project represents "investing in jobs, here and now today, when we need them," Porcari said. "We're investing in an easier, safer, and less congested trip for the 160,000 daily commuters when this project is finished, and by reducing congestion here in the East Bay, we're investing in a greener environment."

Nearly half the project is being funded by money from the American Recovery and Reinvestment Act of 2009. The $197.5 million in federal stimulus money is an example of how "the federal government was there when we needed it, Garamendi said.

The two-lane, 3,389-foot bore was expected to be finished in spring 2014 and would eliminate the need for the existing central bore to alternate between westbound and eastbound traffic for the morning and evening rush hour.

Garamendi, who lives in Walnut Grove, had his office in San Francisco during his eight years as the state's insurance commissioner and lieutenant governor, and said he traveled through the Caldecott Tunnel nearly every day.

"This was my commute route morning and night, and it was just awful," he said. The project "is really an important one for everyone in this area."

The construction of the tunnel, being done by the Sylmar-based firm Tutor-Saliba, would begin with crews setting up their staging areas and building a temporary sound wall at the west portal. Crews would be working from both sides of the tunnel, excavating at a rate of one to two yards per day.

The noise buffering was part of a settlement with a consortium of community groups known as the Caldecott Fourth Bore Coalition that sued Caltrans in 2007 over environmental concerns related to the project.

Assemblywoman Nancy Skinner, D-Berkeley, whose district encompasses both sides of the tunnel, said she thinks those constituents are "very pleased now" with both the settlement and the prospect of a decrease in pollution from cars idling in traffic on either side of the tunnel.

Gov. Arnold Schwarzenegger had been scheduled to attend Friday's ceremony, but instead had to travel to Southern California because of a series of severe storms that caused significant damage to the region.

Schwarzenegger released a statement about the tunnel project, saying that it "is a perfect example of creating jobs for hardworking Californians while improving California's transportation infrastructure."

The fourth bore comes nearly a half-century after the third bore was added to the tunnel in 1964. The original two bores of the tunnel opened to traffic in 1937.

"Today's really a historic day" for Bay Area transportation, Caltrans director Randy Iwasaki said.

A Web site for the project, www.caldecott-tunnel.org, has been set up to allow local residents to follow the progress of construction on the fourth bore.