East Bay Times: Federal funding gap demands a cheaper option for BART extension

But then, in 2018, it all changed, supposedly to appease some downtown merchants. From then on, the VTA staff has been struggling to plan for a single-bore tunnel, about 53 feet in diameter with platforms buried eight stories underground, that will require tunnel lining twice as thick as originally planned and excavation of millions more cubic yards of soil. If the BART extension project fall over…