Earlier quoted context omitted.
Caltrain has passing tracks at Sunnyvale and Brisbane. There are joint plans with CAHSR to add 4-track segments at Millbrae, San Mateo (between Hayward Park and Hillsdale), Redwood City, and Palo Alto (California Ave). The Millbrae tracks are part of the new station design: they are removing one of the 3 BART tracks (superfluous because BART terminates at Millbrae) and using the space to construct two dedicated HSR t…
Ah, thanks for the reminder there are passing tracks already. Are passing tracks really practical? Wouldn't they have to be extremely long to accomodate high speed trains mixed with local Caltrains? I have a hard time picturing this all working out even under ideal circumstances.
It occurs to me that this might be why they've chosen those particular areas. Sunnyvale, Redwood City, Hillsdale, Millbrae, and South San Francisco (just south of Brisbane) are all baby bullet stops, where all of the local, limited, and express trains stop, and so you can reliably count on every Caltrain stopping there and letting a HSR train pass. Cal Ave is the odd one out, but it still has local + limited service.