Picture a set of binoculars — only a pair the size of a low-rise building. That’s the shape of BART’s Transbay Tube — the dual-bore, 3.8-mile passageway that connects the West Oakland Station to San Francisco’s Embarcadero Station. Every weekday during peak commute hours, more than 60,000 BART riders cruise through the tube. What most don’t know is that they’re in a trench on the floor of San Francisco Bay.

Bay Curious listener Jennifer Schulz rides through the tube a lot and can’t help but to think: What if there was an earthquake? How safe is the Transbay Tube? Would it crack? Would bay water flood into my jam-packed BART car? Could I be trapped?

Since 2005, BART has been undergoing a major earthquake retrofit. The final phase is expected to begin next year, finishing up some time in 2023. The cost? So far, $1.3 billion.

KQED’s Tena Rubio spoke with Tom Horton, BART’s earthquake safety manager.

Is the Transbay Tube safe during an earthquake?

What I can say is that it’s safer than most other places people are going to be in their working day. I mean, some of the buildings downtown are obviously built to very modern standards and can survive a large earthquake. But most of the buildings in the Bay Area probably would be collapsing in the size earthquake we’re talking about.

Walk us through what happens if there is an earthquake.

First, we reduce the speed of the train down to 27 mph, which gives an operator plenty of time to see what’s in front of him, and see if there’s any cracking or anything of that nature. But our goal is to not stop in the Transbay Tube. If for some reason folks have to exit the train, we have protocols in place to do that.

What would happen? Would it leak?

The tube does get leaks every now and then, as all tunnels do. And BART actually has an active program to plug those leaks when they happen. During the earthquake we expect that the earthquake forces will cause the liner to crack and then you’ll get leakage. Now the tunnel doesn’t collapse. The tunnels are plenty strong enough to stay up. But if you get too much leakage, it fills with water and that’s what we’re trying to prevent.

So if it did crack, can it fill with water and flood?

We have a pumping system. Part of the retrofit is to increase the size of that pumping system so you can at least slow down the rate of fill. The idea is that you can slow it down enough so that people can get out well before the tube floods.

So it sounds like you’d almost want to be in the tube? That it’s safer than other areas?

Unless it’s a very, very large earthquake you’d probably want to be in the tube. Now we talked about the flooding problem. So if you’re in an earthquake that large it would be problematic, but then so is everywhere else in the Bay Area. So it’s kind of a wash, if you will.

To hear more from Tom Horton and the safety of the Transbay Tube, listen to the full episode of Bay Curious at the top of this article.

A Response Plan, Ready and Waiting

All that talk about earthquakes got us thinking — what if something catastrophic did happen in the Bay Area? After the big one, it’s not going to be easy for anyone to get around. So what will happen to people who really need medical care?

Reporter Eli Wirtschafter learned about one unusual tool San Francisco has to address that problem: old Muni buses that have been turned into giant ambulances.

The idea was first used on New Year’s Eve 2010, when big celebrations were planned at the Embarcadero. To provide extra medical support, the San Francisco Fire Department borrowed a 40-foot Muni bus and turned it into a makeshift mobile clinic, treating people who might have partied a little too hard.

From that time on, the idea of having a bus-sized ambulance “just stayed with us,