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Study confirms VTA's single bore tunnel proposal for extension

The single bore tunneling approach will save time and money, and generate significant environmental benefits, authroity officials say.
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An independent study conducted by tunneling experts has confirmed the Santa Clara Valley Transportation Authority’s proposal for a single bore tunnel design on the Bay Area Rapid Transit Silicon Valley extension project to San Jose and Santa Clara.

The results of the independent peer review, which was led by the American Public Transportation Association, were presented at a VTA board meeting Nov. 3. The study confirmed the transit agency’s tunneling methodology, along with some other proposed design innovations, is feasible and safe for the 6-mile extension, VTA officials said in a press release.

Single bore tunnels have become increasingly common in transit systems in Europe and Asia, with recent examples in Spain, France, Dubai and the Netherlands, they added.

The single bore approach will save construction time, reduce the project’s environmental footprint, increase the potential for transit-oriented development, and reduce noise for and disruption to residents. The alternative — switching to a twin bore tunnel design — would cause significant delays and increase costs, VTA officials said.

The study compared single bore and twin bore tunneling methodologies as they related to safety, cost, scheduling and rider experience. Joint venture contractor Kiewit Shea Traylor provided project documents and past studies.

The Silicon Valley extension will connect BART rail service to more than 1.7 million people in Santa Clara County. To be completed in two phases, the first phase (already completed) extended service into the county from Alameda County, while the second phase will extend service from the Berryessa Transit Center into Santa Clara County. That phase is currently is in design and engineering stage.

Contact Progressive Railroading editorial staff.

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