This is true--but then a top speed of 140mph, as asserted by Elon and company, is unlikely to be feasible because the cars involved won't have time to accelerate to that speed before needing to decelerate at a human-comfortable speed for arrival (which then causes knock-on effects on everybody else in that tunnel system, and I hope their braking systems all work perfectly forever).

And we haven't even gotten into how a top speed of 140mph will burn the hell out of street tires.

It's just...dumb. It's not thought out. It's aggressively reality-averse. It's thought-leadery as hell.