How tight?

I don't know ... I have seen claims they are too tight to be workable. Other than vague happy talk, all I can find is the fuzzy diagram from a 2003 document that was part of the Environmental Impact Report process.

When I say in the post that I don't know if its physically possible ... that's part of it. Swinging the central platform tracks so they come in #2 and #3 from the outside, and the tail track so they go out #1 and #2 from the outside, buys some straightening. Probably not enough, though.

When I was sketching out an operations table, I included one empty slot for four full slots on the access track for delays.

On the CAHSR blog, Brandon in San Diego pointed out that Prop 1A requires 5 minute headways on the HSR network, so on the operation model above, with alternation between HSR and Caltrain built in, an argument can be made that 2 1/2 minute headways would be required by the funding legislation. Tighter headways does not increase platform capacity, so if they can arrive at 2 1/2 minute headways, that could be one open slot for each pair of inbound services.

Its parallel arrival HSR / departure Caltrain and parallel arrival Caltrain / departure HSR that is the point of having an egress track on either side of the access track ... eliminating that crossover between access and egress tracks at grade (or at least, putting it off to the mouth of the tunnel, when its a "half-dive" ... cheaper because the tracks have to dive into the tunnel in any event) ... is what that accomplishes.

As for bidirectional operations on the Caltrain egress track, if the Caltrain egress track is taken down first, to dive under the common access track to the tunnel, it can be a central branch, switched to both sides of the two way track out of the current terminal at 4th, which is about 2km away.


I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.

Even better would be another connection between the two outer tracks, so that a Caltrain departure opposite a parallel Caltrain+CHSR arrival is possible.

From the diary:

The only player that strikes me as having the opportunity to say, "wait a minute, here's a fix that won't cost all that much to implement" is Caltrain. But ... under the solution above, they are giving up a 900 ft. platform, connected to the tail tracks, for what could end up being a 800 ft. platform, with only one connection to the tail track, and that connection only available when the closest HSR platform track is empty.

So, yes, the above, which would make it operationally feasible to squeeze 8tph into four terminal platforms, and which may or may not be physically feasible, does knock on to make things even worse for Caltrain. Efforts to squeeze extra capacity out of the same infrastructure tend to generate bad trade-offs like that.

If there is going to be three tracks, the ideal would be an access track on the one side, an egress track on the other, a bi-directional track in the middle with switches at several points along the tunnel, and an adequate 3:6 fan out including as many dives as necessary to avoid blocking movements.

But the TBT is a property redevelopment project using a transit project as its hook, with the location itself the wrong place for a central rail terminus, and while cut and cover tunneling for the station throat can be useful as an excuse to take over and redevelop certain sites, extra money for an adequate platform access or extra tunneling for dives (and its basically tunneling in mud, so it'll be fairly expensive) ... they are kind of "only if someone else pays for that part".


I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.