Caltrain & Prologis Propose 2,500-Unit Railyards Towers in SF

Caltrain and developer Prologis have submitted a formal application to San Francisco for the Railyards redevelopment project, a 20-acre proposal at 4th and King streets that would eventually produce 2,500 housing units across a cluster of towers and 8 million square feet of total development. The timeline stretches 15 to 20 years, which in Bay Area development terms means it’s a serious proposal rather than a napkin sketch, but nobody currently living near SoMa and Mission Bay should hold their breath.

The project has been circling for a long time. SPUR floated the concept of building above the Caltrain yards nearly two decades ago, and the late Mayor Ed Lee mentioned it during his tenure. Prologis, which owns the railyard property, is now putting paperwork behind what was previously just an idea with good bones.

The first phase centers on a rebuilt transit station at 4th and King, with an 850-foot tower rising directly above it. Additional towers would follow at stepped-down heights, with one structure planned at 7th and King streets at a height the published plans decline to specify. If you’re trying to get a sense of scale from the renderings Prologis released this week, good luck. The street-level views show pleasant walkable streetscapes and ground-floor retail. The one rendering that actually shows building heights places them in the far distance next to the Transbay district towers, which reads less like transparency and more like a deliberate choice to avoid a public reaction to massing before the project gains more political momentum. That’s a familiar playbook in this city.

The 8 million square feet breaks down as follows: roughly 2,500 residential units, plus a mix of retail, office, and possibly hotel space with proportions to be determined based on market conditions when each phase gets built. The first phase covers about 2.5 million square feet, with the residential-to-commercial ratio left flexible. That flexibility is either prudent given how much the San Francisco office market has shifted since 2020, or it’s a way of deferring the hard decisions. Probably both.

One of the more significant engineering components involves sinking the Caltrain tracks underground as part of the development. This immediately connects the project to the Portal, formerly known as the Downtown Extension or DTX, the long-discussed and still-unfunded tunnel that would carry Caltrain and eventually California high-speed rail under Second Street to the Salesforce Transit Center. A concrete box already sits under that building, waiting for trains that have not yet been funded to reach it.

Prologis says the Railyards project can proceed with or without the Portal connection, arguing the underground tunnel work can be added later. From a pure construction logic standpoint, that argument is weak. Coordinating major underground work across a single contiguous project is substantially cheaper and less disruptive than reopening a completed site for additional tunneling. Anyone who has watched a utility dig up a freshly paved street will understand the frustration. Still, decoupling the projects politically may be necessary to get either one moving.

The plans also include a public park called the Sixth Street Park, positioned on top of the overpass where the train tunnels begin. On paper it’s an appealing piece of public infrastructure. In practice, parks built above transportation infrastructure require expensive maintenance structures underneath them and often become afterthoughts when project budgets tighten. Worth watching as phases develop.

For commuters, the most immediate significance is what this means for the 4th and King station experience. The current station is a functional but deeply uninspiring end-of-the-line facility. A rebuilt transit hub with mixed-use density around it is exactly the kind of transit-oriented development that transportation planners have been advocating for since the 1990s.

The 15-to-20-year build-out means the full project won’t be complete until somewhere between 2041 and 2046. Phase one alone will reshape the edge of Mission Bay. Getting through San Francisco’s permitting and environmental review process while managing a project of this scale, phased across two decades, will test Prologis and Caltrain in ways the renderings don’t show.