Elastic demand requires free-flowing masses. I'm quite sure New Yorkers or Londoners would be able to fill as many new subway trains during the rush hour as you could humanly add to the rail network, at least on the sections that are most commonly shared between lines to different destinations.
On the other hand, if the on-ramp of a highway would only let cars through for one minute every 10 minutes (which would be considered a good service interval for any suburban public transit), the demand for roadspace would likely be a bit less elastic. Ditto, if the highway would only go to a set of destinations with no connections.
Motorists can embark on a trip any time, join the highway any time, and take any exit, and continue from there to local destinations. This free schedule suits way more people than fixed departures to fixed destinations using public transit.
Only in a densely built city you can achieve the same: people sharing segments of public transit before diverging to a number of different destinations.
On the other hand, if the on-ramp of a highway would only let cars through for one minute every 10 minutes (which would be considered a good service interval for any suburban public transit), the demand for roadspace would likely be a bit less elastic. Ditto, if the highway would only go to a set of destinations with no connections.
Motorists can embark on a trip any time, join the highway any time, and take any exit, and continue from there to local destinations. This free schedule suits way more people than fixed departures to fixed destinations using public transit.
Only in a densely built city you can achieve the same: people sharing segments of public transit before diverging to a number of different destinations.