VTA Report Supports Single-Bore Option for BART Silicon Valley Project

A single-bore tunnel is the smarter, faster, and more community-friendly way to complete the final phase of the Santa Clara Valley Transportation Authority’s (VTA) BART (Bay Area Rapid Transit) Silicon Valley Extension, according to a VTA-commissioned study released this week. A link to the report can be found here.

The findings of the report, assembled by VTA consultants, suggest that a twin-bore approach could increase costs by as much as $600 million, and would not allow the extension to open any sooner than 2037, the projected revenue date of the single-bore design. The twin-bore design would also involve impactful cut-and-cover construction in downtown San Jose, something that officials plan to avoid using the single-bore approach. According the report, VTA staff will continue to look for cost-savings opportunities but will not recommend further analysis of the twin-bore design.

Notably, the single-bore tunnel has been approved since 2018. The VTA and BART Boards of Directors endorsed the plan, and the Federal Transit Administration has issued its Record of Decision, clearing the way for engineering and construction to proceed. Switching to a twin-bore design would require restarting environmental reviews, repeating engineering work, and buying new tunnel boring machines – delaying progress and increasing costs.

In May 2022, VTA awarded a progressive design-build contract to Kiewit Shea Traylor JV. Stage 1 involved preconstruction activities, including, planning, design, scheduling and cost estimating, as well as advance construction activities. Upon successful completion of Stage 1, the PBD contract would then proceed to Stage 2, which would include major construction activities including tunnel boring. However, as Stage 1 evolved, VTA and the contractor were unable to agree on cost proposals, according to a report on Metro-magazine.com. Engineering News-Record (ENR) reported that project cost estimates were approximately $7 billion at the time the Stage 1 contract was awarded. More recent estimates were approximately $12.7 billion. In June, VTA decided not to proceed to Stage 2 and seek another contractor.

BSVII Project is a six-mile, four-station extension that will bring BART service from Berryessa/North San José through downtown San José to the City of Santa Clara, includes three stations with underground platforms (28th Street/Little Portugal, Downtown San José, and Diridon), one ground-level station (Santa Clara), a train maintenance and storage facility at Newhall Yard, and additional facilities. Five miles of the six-mile alignment were planned to be constructed in a large diameter single-bore tunnel, with the remaining one mile at-grade rail.