How do the “bullets” work? Passing local trains when they’re stopped on stations? I didn’t notice a third set of rails anywhere for that.

There are three passing points on the line, where trains can pass each other without interrupting opposite-direction traffic. From North to South, they are…

• Between 22nd Street & South San Francisco, with Bayshore accessible via the 'local' tracks only.

• Between Redwood City & Menlo Park.

• Between Sunnyvale & Santa Clara, with Lawrence accessible via the 'local' tracks only.

Today, the northernmost and southernmost passing points are used by the Limited or Baby Bullet services to overtake the Local services. The service being passed has the middle station (Bayshore or Lawrence) as a scheduled stop, and remains in the station until they observe either a clear signal, or until they observe the faster service passing.

The passing point between Redwood City & Menlo Park is mostly used when a service (any service) is running slow, to allow on-time services to overtake. This is especially important when the slow-running service is a Local.

Finally, there are crossovers placed frequently along the line, often every 2-3 stations. These are used most often when maintenance is being performed on one section of track, or if a train is disabled. They are not used during normal operations.

There's pretty limited passing on the routes judging from the schedule [0]. It looks like there are a couple sections along the corridor where there's an extra rail for passing [1].

[0] https://www.caltrain.com/schedules/pdfs?active_tab=route_exp... [1] https://hsr.ca.gov/wp-content/uploads/docs/programs/statewid...

They don't really pass, except in Burlingame and Sunnyvale. I think they basically just leave enough room between regular trains for the bullets to skip some stations. This is one of the reasons I think the SJ-SF segment of HSR may end up being a bottleneck.