There is a problem with the ridership estimates and it is more than that the estimates are wrong. It is because the estimate is not based on a door-to-door transit system like Tokyo has to support the high-speed system. You have look at high-speed rail as an incomplete system that drops you off at the terminal and then you are on your own to get to your final destination. Getting to the high-speed terminal from your location is the same problem. You have to rely on poor or nonexistent public transportation.

High-speed rail works in Japan because the population is mainly crowed along a straight line on the west cost. Tokyo does not have any areas like Los Altos or Los Altos Hills to service with local transportation. If you look at a map of the private, semi private, and municipal transportation system, they has essential door to door service and they travel with very little baggage. (Next time you are at the airport, just take a look at the baggage that is carry on the airlines from here to LA. – or at the carousel.)

Check out the Tokyo transportation system map
Web Link
and you will see why high-speed rail works there and will not be very effective here.