ABSTRACT
An independent integrated cost and schedule life-cycle risk analysis has been used to compare the viability of two competing tunneling options even at different levels of design maturity. This paper describes the process used to provide the Santa Clara Valley Transportation Authority (VTA) with a comprehensive decision-making basis using comparative risk profiles for two tunneling alternatives; a single large diameter tunnel versus two smaller twin tunnels to extend San Francisco’s Bay Area Rapid Transit (BART) service into downtown San Jose. VTA also conducted a fact-finding mission along with BART to Barcelona’s Metro Line 9 (L9) subway to allow first-hand evaluation of a single-bore system. Construction and system risks were qualitatively assessed and quantified in terms of cost and time to compare the cost and duration of the two options, including the differences in Operations & Maintenance (O&M) costs for the first thirty years of operation.
