This story aired in the June 16, 2025 episode of Crosscurrents.
As far as big public projects go, the Salesforce Transit Center exerts a kind of unmistakable presence in downtown San Francisco. It’s huge—spanning nearly four blocks. And it’s meant to connect the greater Bay Area to the city through a network of regional transit lines.
There’s a 5 acre park perched on top, and on ground level, you can find food and shops operating out of the terminal’s retail spaces.
What most people who visit don’t know is that beneath the streets and sidewalks are empty, cavernous spaces that stretch the length of the transit center above.
This is the Trainbox, the space built out and reserved for the rail lines that MAY someday connect downtown.
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Story Transcript:
Voices from inside a stairwell at the Salesforce Transit Center, followed by exclamations of excitement and awe.
REPORTER: Those “oohs” and “ahhs” are from a tour group of grad students from UC Berkeley. In the group are engineers, urban planners, and environmental scientists in training. They all have one thing in common: a wonky passion for transportation and city infrastructure.
And it’s because of that passion that they get a glimpse of massive, empty concrete space underneath downtown San Francisco.
It’s called the “Train Box.”
A voice calling out into the Train Box.
REPORTER: Right now, the Train Box is empty. It was built for two futures that don't exist yet.
One, it will be the last stop on Caltrain’s long-awaited Downtown Extension, so Caltrain passengers can finally go further than Fourth & King. And two, it will be the Bay Area terminus of the California High Speed Rail system.
The Train Box was designed to fit six trains—four from Caltrain and two from high speed rail, which means it’s huge.
It’s about four stories high and stretches for almost four blocks between Beale and 2nd Street. That’s about a third of a mile long.
The group enters the Train Box from a service stairwell and they fan out like spelunkers exploring a cavern. Our guide is Lily Madjus Wu from the Transbay Joint Powers Authority, which owns and operates the Salesforce Transit Center and the Train Box. She attempts to herd the group back together.
Lily Madjus Wu: Let's start right here. I know you're super excited. Um, okay guys, this is B two level, basement level two.
REPORTER: The box exists in a kind of liminal space. It has functioning power and you can hear the endless hum of the ventilation system. It has access doors and stairways ready to be used. The elevators have placeholders for buttons that will eventually take passengers from the street-level to the concourse and the platform. There’s a skylight—you can see in the Salesforce Transit Center right now —that allows natural light to pour into this subterranean space.
There’s something else at the southwest end of the Train Box that signals what this space could become, at least to an expert’s eye: four 20 foot-high square concrete panels called knockout walls.
City planning PhD student Mike Muncia explains.
Mike Muncia: So right now they, they have to have a wall there 'cause there's dirt behind it. So that wall is holding the dirt from coming back in.
REPORTER: So these concrete panels are the only thing between us and tens of thousands of pounds of dirt and rocks.
Mike Muncia: But once that dirt's removed, when they actually build the tunnel, they'll be able to just take that wall down and build the platforms and tracks directly in here.
REPORTER: Once that tunnel is complete and the rails are laid and trains for Caltrain and High Speed Rail can start operating, the Train Box will transform into downtown San Francisco’s train hub, or as some officials like to call it the “Grand Central Station of the West.” It’s official name? The Portal.
That’s the plan, anyway.
Because in order for any of this to happen,what the Train Box really needs is money. A lot of it.
The Train Box has already cost about 730 million dollars so far. The Transbay Joint Powers Authority estimates they need another 7.5 billion dollars to make it operational.That includes finishing the 1.3 mile Downtown Rail Extension for both Caltrain and high-speed rail. The Biden administration committed about 3.4 billion dollars to the project in 2024. But in order to access that money, the Authority needs to secure matching funds from local and state sources. And with the state budget tightening and a Trump administration hostile to clean energy initiatives, getting more dollars seems unlikely for now.
But for San Francisco transportation officials, it’s not really a matter of if the project will happen, but when.
Adam Van de Water: And so planning for its inevitable future is important.
REPORTER: Adam Van de Water is the executive director for the Transbay Joint Powers Authority. Building the train station before even knowing when the train tracks might exist seems out-of-order, but Adam says waiting on those projects would have made even less sense.
Adam Van de Water: Had we not built the train box first, we would then be trying to operate a transit center with a rooftop park and all that retail, and then digging underneath it at significantly higher risk, higher cost, and higher engineering challenges while trying to maintain those buses and that flow of activity.
REPORTER: The downtown extension for Caltrain is supposed to be finished by the early 2030s. And the California High Speed Rail has no firm opening date in sight.
Adam Van de Water: You wanna talk about patience, you need to have some patience for that. It's gonna take a minute.
REPORTER: But even with the grand opening of the Train Box at least a decade away—talk about patience—the Berkeley graduate students on the tour still found things to marvel at. Jacob Champlin is a master’s student in city planning and transportation engineering. He says it’s exciting to check out a huge project like this at an unfinished stage.
Jacob Champlain: I was expecting a gigantic concrete box and I got gigantic concrete box, and I think it's gonna look incredible. I love the light source here that we're looking in front of. I think that's amazing artistic work, and I'm glad that they're trying to think about as many things as possible when designing this entire concourse.
REPORTER: For others, like Ivette Torres from the Inland Empire in San Bernardino County, touring a structure like the Train Box made her think differently about the transportation projects in her own community.
Ivette Torres: There's rail all over me, warehouses, ports, and not any public transit. So being in an area where there's a lot of public transit, it's really amazing. And I hope in my work to bring more transit and electrify those fossil fuel industries, and create work that is sustainable for folks.
REPORTER: The groundwork for this future vision of transportation in the Bay Area is set, literally, in concrete in downtown San Francisco. And for transportation advocates, the Train Box represents a future that inches closer, with each day. But maintaining public interest and the political will to move these projects forward, is another story altogether.