I've often heard the argument about urban transit being more useful due to serving larger numbers of people, and although it sounds persuasive, I've come to the realization that it's pretty much bunk. In order to determine the true value of a piece of transportation infrastructure, you should measure it in terms of the total amount of transportation it provides (in terms of passenger kilometres) rather than the number of people it serves.
One can compare the passenger KMs (and therefore usefulness) of an urban transit line like the
Yonge–University–Spadina line in Toronto to a potential HSR between Toronto-Ottawa-Montreal, by multiplying the distance the average passenger would travel by the number of passengers. The YUS line has average weekday ridership of 714,210 persons. It extends north from Union in two separate arms each of about 15km. Obviously most people will not be traveling from end to end so if we assume the median trip is 1/2 of one of the arms (7.5 km), then it would provide
5,356,575 passenger/KMs of transport per average weekday.
Now, the distance between Toronto-Ottawa-Montreal by "way the crow flies" is about 520 km. The exact route it will take will likely be longer. If we use the French
TGV for the comparison, its train capacity ranges from 345 to 750 people depending on the route. If we assume ours are somewhere in the middle (548) and they're normally about 3/4 full that's 411 people per trip. If the train runs every hour between 7am and 11pm (16 trips per direction per day) then it would provide a total of
6,839,040 passenger/KMs per day.
Obviously without actually having a HSR line with real details to use, we can't make an exact comparison. But the point is, HSR has the potential to provide just as much transportation as urban rail transport does.
The same kind of debate sometimes arises around inner urban transit vs commuter rail and honestly, there's no rational reason to be biased as to whether it's fewer people making longer trips or more people making shorter trips, or if the average person uses it every day or a couple times per year. Long and short distance travel are both of vital importance to the public.