Overview

• The August analysis estimates the single-bore tunnel will save about $600 million versus a twin-bore alternative and limit disruption to downtown streets and utilities.
• VTA officials argue that reverting to a twin-bore design would inflate costs by at least $600 million without advancing the current 2037 delivery target.
• Consultants from Gall Zeidler and retired BART engineers have challenged the report’s assumptions, calling the twin-bore cost estimate overinflated and the comparison flawed.
• The agency plans to present the cost, risk and impact report to its board and oversight committee and affirms it will not pursue further twin-bore evaluation.
• Phase 2 of the six-mile extension now carries a $12.7 billion budget, retains a funding gap of over $700 million, and faces tunneling delays that could push start into 2027.