The Santa Clara (CA) Valley Transportation Authority (VTA), currently underway with a $4.7 billion, 16-mile Bay Area Rapid Transit (BART) extension into downtown San Jose, is considering boring one tunnel, instead of two, to lower costs and reduce the time traffic and local businesses will be disrupted.
The VTA estimated that tunneling into downtown could cost $500 million but that the single-tunnel option could save $50 million and reduce the four-year tunneling schedule by 10 months. BART officials prefer the existing two-tunnel, single-track strategy, which is the global standard for this type of rail.
Speeding up the VTA's decision is a $1.5 billion Federal Transit Administration grant deadline, requiring them to vote soon.
The number of projects requiring tunneling has increased in the last several years because new technology has made it a cost-effective and efficient option. The Wall Street Journal reported that German tunnel boring machine (TBM) manufacturer Herrenknecht now serves as many as 100 projects each year, up from roughly 20 in 2000. New York City officials say TBMs have driven the cost of city tunneling projects down significantly.
That doesn't eliminate the possibility of tunneling problems. A TBM dubbed Bertha, which carved out a new tunnel for Seattle's Alaskan Way Viaduct project, broke down in December 2013. The incident put the TBM out of commission for two years. After resuming operations in late 2015, Bertha was forced to stop digging in January 2016 when a sinkhole formed near its path. Washington Gov. Jay Inslee stopped boring operations until general contractors developed a plan to improve tunneling operation monitoring.
Tunneling has also been a recent focus of SpaceX and Tesla founder Elon Musk. His new TBM venture, called The Boring Company, has reportedly been in very preliminary conversations with Trump administration officials about the possibility of boring a hyperloop tunnel between Washington, DC, and New York City.
Most recently, The Boring Company received permission from the city of Hawthorne, CA, to dig a 2-mile tunnel under city streets to test an alternative transposition mode, which uses electric sleds to move vehicles at speeds of up to 125 mph.