Since much of that growth in population has been up on the "mountain', I would think that Tehachapi, would be the end of the best potential end point for the population base of likely commutes and/or other potential "rail market" trips to the jobs and/or services (medical, education, business, cultural, personal) to the AV itself, ditto Santa Clarita, ditto the other stations.

This Kern County extension would offer those folks direct access to air service out of Burbank Airport, and full connections at Union Station for other rail destinations, and when the LAUPT run-through is completed single train service all the way to San Diego. That is, if we really wanted to have a truly "first world" regional and interregional rail passenger system....?

Of course, we'd cut over a half an hour off of that travel time, using the new Lang to 118 HSR/Toll Road tunnel under Saugus Mountain, for direct service to Burbank Airport and LAUPT, making for much travel times, competitive even in non-peak periods.

Not easy you say? Another track from Lancaster up the east end of Tehachapi at a minimum on the Kern County end, but easily doable.

And, just "imagine" if you could offer that kind of "first world" utility of rail passenger service (not just "peak" commuter service) all day, frequent, and reliable regional and interregional rail passenger service....?

And, I'd say, that given our ever increasing isolation and impaired access, increasingly caused from gridlock itself, that we'd have excellent ridership from many of these "outlying" "edge" centers, into and out of the major urban centers.