An independent study by world renowned tunnelling experts, confirms the Valley Transportation Authority’s single bore tunnel design is the right approach to deliver the BART Silicon Valley 9.65 km (6-mile) extension into San Jose and Santa Clara.
The results of an independent peer review, led by the American Public Transportation Association (APTA), was presented at the VTA Board Meeting on November 3 and shows VTA’s cutting edge tunnelling methodology along with some of the proposed design innovations is deemed to be feasible, appropriate, safe, and efficient.
Single bore tunnels are increasingly being utilized for transit projects in Europe and Asia, with recent projects in Spain, France, Dubai, and the Netherlands.
This single bore approach by VTA to build the vital BART extension will save construction time, reduce the station footprint and property needs, increase the potential for transit-oriented development, reduce disruption to city streets, neighbourhoods, and businesses. The approach reduces many of the environmental impacts occurring during construction. In addition to losing the aforementioned benefits, changing to a twin bore tunnel project would cause significant schedule delays and cost increases.
The study included review of trade-offs between the single bore and twin bore designs related to safety, passenger experience, cost, and schedule. It was informed by extensive project documents and past studies, recent global tunnelling projects, and a key proposed innovation from Kiewit Shea Traylor, the joint venture contractor for the tunnel and trackwork.
APTA was engaged to coordinate an independent review of the project’s tunnelling method as part of a design review request from VTA Board member and San Jose Mayor Sam Liccardo, approved in May by the VTA Board of Directors. The findings of a previous independent comparative analysis of both tunnelling methods in 2017 helped lead to the single bore approach and current concept.
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