Is BART's South Bay extension tunneling too deep? Some perspective

Some folks think that at 90 feet underground, some of BART's new South Bay platform plans, built underneath VTA's tunnel system, is not rider friendly. 

In the case of BART South Bay, how deep is deep?

The new BART South Bay station platforms will require a descent of 70 to 90 feet. That turned out to be optimal to balance engineering with passenger utility. 

"One of them being the soil conditions, the other being the appropriate amount of soil above the top of the tunnel to make it structurally sound and safe," said BART/VTA Project Spokeswoman Bernice Alaniz.

Putting the tunnel that deep causes far fewer issues for the people on the surface during the construction period. It's also critical to protect lots of buried things. 

"Going down a major east-west corridor in the city of San Jose, there would be a significant amount of utilities. This  deeper level tunnel actually allows us to bore underneath those utilities," said Ms. Alaniz. That includes water main, gas pipelines, electrical equipment, sewers, drainages, buried structures and other things known and unknown. "And especially in a very historic area, there's not a very full documentation of everything that may be there," said Alaniz. 

And, there will be new, state-of-the- art conveyances. "We will have a combination of high speed elevators that will get people down quickly. We also will have escalators. And, as you all know, some of use will stand on those escalators, some of use will also use that momentum and start walking and then we have stairs," said Alaniz. Yes, some people prefer stairs.  

But how deep is deep? Of the 181 or so subways worldwide, the deepest metro system is in North Korea's averages 360 feet down. The deepest underground station: Kiev, Ukraine; 350 feet down. Beijing; 308 feet. The Moscow Russia Subway and Barcelona systems are both 243 feet deep. D.C. Metro; 196 feet. 

New York City's deepest station; 173. Going shallower, London is at 136 feet, Paris is 118 feet, Seoul and Tokyo, about 90 feet; just like San Jose. In other words, it would be as tall as a nine-story building with elevators and escalators. By the way, BART's Embarcadero station is 60 feet down.