Take another look at the success of Japan’s trains and the population/urbanization density.
One reason the commuter trains are so successfull, is that most people can WALK to the local Train Station, then WALK to the job at the other end.
And those are not “Bullet” trains. BUT, the bullet trains connect at each end to other mass transit stations, so you travel to your destination building once you arrive in your destination city.
In addition to the infrastructure for the rails and high speed trains, you need a way to get folks to the stations and from the stations to the buildings.
In most US transit systems I have seen, commuter rail must put large parking lots (or structures) near the stations to enable the riders to park the “Terminal” commuting device (car or SUV) in order to access the train…very few I have seen are without them.
Take the Metro in DC, for instance.
The outlying stations all have large lots; the routes all go to downtown DC, via the Pentagon, where many many bus lines originate/terminate (for terminal commutes) or through the many stations in the downtown area, where 90% of the offices are within walking distance of SOME metro station.
Some of the parking lots even go so far as to prohibit parking before 9AM, so that commuters will not get all the spaces, and day trip/shoppers are able to use the Metro to enter the city, leaving the cars behind.
And that is one of the issues in the West…not everybody on the freeway is going to the same spot. (Although sometimes it feels that way!).
San Diego is so spread out, there is not a single point everyone has to pass through to get to their destination. So to make the Light Rail work, they will have to find a way for folks to get to the offices once they arrive close to town. Ridership is aparrently picking up; perhaps they are solving that problem.
Unfortunately, most modern american commuters consider a walk of a mile to be excessive… <