The track can be used for 1-2 centuries (as they have been in Europe). That includes many refurbishments and replacement of steel but much of the construction cost will be low per passenger.
Older tracks can't be used for high speed trains. In France, all the new high-speed lines are constructed for this usage (lot of straight lines). On older lines, an high-speed train will be at the same speed as a normal commuter train.
He didn’t say they could. But tracks built today can be used forever, because wheel-on-rail technology has a hard limit at Mach 0.5 and we’ll never have faster trains than we have today.
