Updated January 7, 2011

What does the project entail?

A fourth tunnel bore will be built north of the existing three tunnel bores at the Caldecott Tunnel on State Route 24 between Oakland and Orinda. Two smaller projects that will help traffic flow in the area, as well as a project to landscape the construction staging areas after construction, are also part of the Fourth Bore Project. When the project is complete, two tunnel bores will accommodate westbound traffic and two tunnel bores will accommodate eastbound traffic.

How big is the tunnel?

The new fourth bore will accommodate westbound traffic through an arch-shaped tunnel 3,389 feet in length and 41 feet in width at the base, with two 12-foot lanes, a 10-foot shoulder on the right and a 2-foot shoulder and 3-foot walkway on the left. Seven cross passages will connect to the existing northern bore that will serve as an emergency escape route for both tunnel bores.

What is the project schedule?

Work began in late January 2010. The tunnel will take about four years to build. For more information on project schedule click here.

How much will it cost?

The project was originally allocated $420 million. However, thanks to favorable market conditions the construction bids were lower than anticipated. The adjusted budget for design, administration and construction of the Fourth Bore Project is $390.8 million.

Who is funding the project?

The project uses funding from a number of sources, including federal, state and regional sources. The two largest sources of funding on the project are American Recovery and Reinvestment Act (ARRA) and Contra Costa Measure J funds. See Funding.

Who are the project partners?

The project partners are Caltrans, the Contra Costa Transportation Authority and the Alameda County Transportation Commission.

Who is the contractor?

The contractor on the main tunnel project is Tutor-Saliba Corporation of Sylmar, California.

Will the contractor work from both ends of the tunnel?

Yes, by tunneling from both directions, the contractor will save both time and money. Tunneling on the east side began in August 2010. Tunneling on the west side should begin in February 2011

Will there be blasting on the project?

That is up to the discretion of the contractor. Blasting is an effective way to break up hard rock. However, blasting is too noisy to be done at night, and the third bore would be closed during blasting for safety reasons. Thus, noise and traffic restrictions would allow only a short period of time near mid-day for blasting. The contractor would need to determine whether such restrictions make blasting a cost-effective and efficient method of loosening hard rock.

Will the contractor work at night?

The contractor will work at night. In terms of ambient light, it makes little difference inside a tunnel whether it is day or night. The tunnel must be illuminated at all hours. Working at night will allow the contractor to complete the project much more quickly.

Working at night? Won't that be noisy?

Night work will be restricted. No blasting or off-hauling of tunnel spoils will be permitted at night. The surrounding earth will substantially muffle any noise generated inside the tunnel. nighttime noise.

Are you using a tunnel boring machine?

No. Tunnel Boring Machines (TBMs) are custom made for each job. They are very effective in the right circumstances, but also very expensive. TBMs work best when the surrounding rock is consistently hard throughout the boring area. Fractured rock, the type at the Caldecott, would tend to collapse around the machine, slowing the operation. The New Austrian Tunneling Method is a better fit for the job.

What is the New Austrian Tunnel Method?

The New Austrian Tunneling Method (NATM) is a process of sequential excavation in which the length of the excavated section is based on the surrounding geology. The rock is assessed on a scale of one through five, with one being the hardest rock. The harder the rock, the farther the workers can tunnel before installing supports.

Why not have three bores open in the westbound direction in the morning and three bores open eastbound in the evening? Wouldn't that be most beneficial?

Having three bore open in one direction would have little benefit because there are only four lanes available in each direction. Three westbound (or eastbound) tunnel bores would feed six lanes from the tunnel into four lanes of the freeway, creating a bottleneck.

Where will the dirt from the tunnel be dumped?

Spoils – the material excavated from the tunnel – will be transported to three locations. Up to 280,000 cubic feet of clean spoils - material that does not contain hazardous substances - will be stockpiled on Treasure Island for future use by the Treasure Island Development Authority.

Spoils that are considered hazardous will be transported to Clean Harbors in Buttonwillow, California or Waste Management in Kettleman City, California. Until excavation begins, there is no way to accurately estimate the amount of soil contaminated with hazardous material. According to Caltrans's studies, the most likely contaminant on the project would be naturally occurring hydrocarbonswithin the tunnel, or aerially deposited lead, which would have accumulated on the ground near the portals, a remnant of the time when vehicles ran on leaded gasoline.

The project also has a printable fact sheet. Click here.