When BART and Santa Clara Valley Transportation Authority first discussed plans to send trains rolling under downtown San Jose, transit officials contemplated a design with two tunnels that would burrow for miles under the street.
That idea turned out to be monumentally expensive and time-consuming, and would have set the Silicon Valley extension back years, according to a new cost report released on Monday. The report helped validate a decision that VTA’s board made years ago, to pursue a more modern and less-invasive single bore configuration.
Single-boring, it turns out, will save VTA at least $600 million while helping ensure it can open the second phase of BART-to-San Jose by 2037, according to the report’s findings. Additionally, single-bore construction minimizes disruption to surface streets, since it requires drilling a hole deep underground, rather than using the “cut-and-cover” method of digging a shallow trench and then filling it…