What would happen if we switched to twin bore now?

In 2008, before the BART Extension Program was broken into two phases, a twin bore configuration with cut-and-cover stations was relatively advanced. However, those plans are now nearly 15 years old and would require major updates and redesign to meet the current codes and standards in addition to a new environmental clearance process. This would add years to the schedule and further delay revenue service. With only a few months to go before VTA anticipates awarding the first major construction contract for the project, such a change would add significant schedule and cost impacts and negate all the efforts and benefits of participating in the FTA Expedited Project Delivery funding program. Any potential cost savings, if determined, would also be exponentially negated with schedule delays and escalation.