ORINDA -- Caltrans began tunneling Monday on the Caldecott Tunnel's fourth bore, and officials predicted that the Highway 24 project to ease congestion will cause only minor or modest traffic disruption over the next three years.

"We've waited a long time for the tunnel to begin. Today, we dig," Bijan Sartipi, Caltrans District 4 director for the nine Bay Area counties, said during a short ceremony in Orinda.

A 130-ton excavation machine called a roadheader carved out a few inches of soil. Dust and soil flew high into the air to cheers from construction crews, politicians and transportation officials crowded into an excavated clearing for the extra two lanes to be added to the six-lane Caldecott Tunnel.

The new bore is scheduled to open in late 2013.

Victor Mendez, administrator of the Federal Highway Administration, said the tunnel is the second-largest highway project in the United States made possible with funding from President Barack Obama's economic stimulus act. The federal bill provided $197.5 million of the $420 million project cost.

Caltrans officials said the project is not expected to have big effects on traffic because most of the construction is inside the hills between Orinda and Oakland. However, many nighttime closures of the third bore will be necessary to dig seven escape tunnels to connect the third and fourth bores, said Vince Bonner, Caltrans senior design engineer.


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Some lane closures on Highway 24 will be needed later in construction when Fish Ranch Road onramps to Highway 24 are rebuilt and lengthened for safer access to the freeway, Bonner said.

One temporary construction feature that bothered many Highway 24 drivers was removed over the past two weekends when Caltrans took down a K-rail, a concrete barrier, installed just to the right of the westbound portion of the freeway. Many drivers said the rail made them feel cramped, although Bonner said he was not aware the structure caused an increase in accidents.

The concrete barrier was installed as a construction buffer for contractors rebuilding and slightly moving the Highway 24 off-ramp connecting with northbound Highway 13 into Berkeley. That new off-ramp is set to open in September.

Contact Denis Cuff at 925-943-8267. Read the Capricious Commuter blog at www.ibabuzz.com/transportation. Follow him at Twitter.com/deniscuff.