BART moved one step closer to reaching downtown San Jose and Santa Clara Thursday when the board of directors of the Santa Clara Valley Transportation Authority unanimously approved the first major contract to build a BART extension into the heart of Silicon Valley.

VTA spokesperson Bernice Alaniz said Thursday the first contract package for the tunnel and trackwork, for $235 million, has been awarded to Kiewit Shea Traylor, a joint venture. It is a progressive design-build contract.

VTA is building the BART extension to Santa Clara County. The first phase of the extension brought trains to Milpitas and San Jose's Berryessa neighborhood in late 2019.

The second phase is a six-mile-long extension from the Berryessa BART Station to downtown San Jose and ultimately to Santa Clara.

The contract approved Thursday will be carried out in stages, Alaniz said. It will include investigation of innovations, engineering and design, open book cost estimates and the work schedule.

The first stage is to begin this month and last through December 2023, setting the stage for major construction which includes boring a tunnel under downtown San Jose.

Three other contracts will be considered in the future for the systems, stations and the Santa Clara Station and maintenance yard.

VTA's BART Project is a six-mile, four-station extension that will bring BART service from Berryessa/North San Jose through downtown San Jose to the City of Santa Clara. It includes three stations with underground platforms (28th Street/Little Portugal, Downtown San Jose, 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 is planned to be constructed in a large diameter single-bore tunnel, with the remaining one mile of surface rail track.