Bringing Bay Area Rapid Transit (BART) to Silicon Valley has proven difficult due to costs and because BART and the Santa Clara Valley Transportation Authority (VTA) officials haven’t always seen eye-to-eye, but on Friday the agencies made a breakthrough.

Officials have agreed to use what is known as a “single bore stacked platform configuration,” meaning two boarding platforms will sit one above the other in a single tunnel, rather than two tunnels with one set of tracks side-by-side. BART officials had previously expressed operational concerns with the single bore option, but last week seemed satisfied with a new set of compromises the agencies worked out.

VTA’s BART Silicon Valley Phase II Extension Project is a six-mile, four-station extension from Berryessa/North San Jose through downtown San Jose to Santa Clara. The project includes a tunnel, three underground stations (28th St./Little Portugal, downtown San Jose and Diridon Station), an at-grade station in Santa Clara, and a storage and maintenance facility.

“It remains essential for VTA to work with BART to identify an acceptable configuration because BART will ultimately operate the system,” Bernice Alaniz, BART Silicon Valley business operations and communications director, said in a recent memo.

The BART project alignment. Image courtesy of VTA

One of BART’s operational concerns with the stacked configuration was around emergency access to the enclosed stairwells, especially for passengers on the upper levels, who would have to go downstairs to go back up. Another issue was ramped tunnels, which are uncommon along BART routes and would require additional training for operators. Lastly, VTA’s design of the tunnel ventilation system differed from BART’s and would also require operational training.

In response to BART’s concerns, changes are planned for the ventilation facility at 13th St. and Stockton Avenue, which can also be used for emergency evacuations. In addition, revised design concepts reduce four train track ramps to two.

Carl Holmes, BART’s assistant general manager for planning, development and construction, said that the reduction of the ramps was key to their agreement, along with reworking the ventilation stations to allow for the emergency egress of riders and first responders.

“While these challenges and concerns BART expressed exist, there is an opportunity with the single bore stacked configuration to enhance that configuration and address these operational concerns,” he said.

The decision comes after VTA designed 10 percent of the center platform last summer to see if a twin bore option with side-by-side tracks was feasible, but determined that proposal would require a much larger and deeper tunnel diameter, increasing costs by about $4 billion and adding substantial construction risks.

A forum of contractors said that given the size and depth of the tunnel and the risk involved, it was uncertain that VTA would receive competitive bids for the project, and if it did, they’d be much higher than budgeted.

VTA also evaluated two other tunnel configurations, weighing funding constraints, environmental clearances, construction impacts, contracting risks and innovation opportunities, but ultimately landed on the single bore with stacked tracks option.

An illustration of the single-bore, stacked rail option. Image courtesy of VTA

Moving forward

The first 10 miles of the BART Silicon Valley Berryessa Extension Project is in its final testing stages. Passenger service is set to begin in a couple of months. Phase II of the rail project runs from Berryessa across US 101 to downtown (at 13th Street to Stockton Avenue) and continues to Santa Clara station and the yard.

Judging by similar construction occurring in Los Angeles, Chief BART Delivery Officer Takis Salpeas estimated that a 1,200-foot segmented construction project downtown would take about nine months.

The single bore stacked tracks will run 12,500 feet from 13th Street to Stockton Avenue. A twin bore configuration will run east of 13th Street with a station at 28th Street/Little Portugal.

“Over many months, VTA and BART have been sharply focused on overcoming hurdles that have tried to derail the long-time goal of bringing critical transportation solutions to Santa Clara County,” Alaniz said. “…the second, 6-mile phase into downtown San Jose and Santa Clara…radiated progress and partnerships.”

Mayor Sam Liccardo also expressed his relief Friday.

“Many of us were on edge as we looked at some of the cost estimates of the larger bore,” Liccardo said, “and the $4 billion was making everybody’s eyes pop out. Thank you for finding this creative design solution.”

Contact Lorraine Gabbert at [email protected]