Discussion on:

It runs in tubes: the first high-speed rail, circa 1870

An interesting fact which i first encountered in Martin Gardner's note in the original "Annotated Alice" is that a train running on an absolutely straight track between two points (that is, one which cuts a chord of the Earth's surface), under the influence of gravity alone, will roll from one end to the other.

And a trip for any distance will take precisely the same time as a trip over any other distance, because, essentially, the train is the bob on a pendulum with a length equal to the Earth's radius.

Wouldn't be all that great for trips across town, but NYC to LA, it would be faster than Concorde.

And free, powered only by gravity.

(Well, once you spent the trillions to dig the tunnel, which would get pretty far down around Kansas City...)

You'd have to ensure there were no air leaks etc. Although I've often
wondered about the cost the air in tunnels adds to running a subway.
I've wondered what the costs would be to build and run a mag-lev in
vacuum tunnels.

Two problems with this (except the practical matters you've
highlighted):
1. The approximation that a pendulum's period is independent of its
peak deflection only applies for small deflections, i.e. short journeys
in terms of your train.
2. If moving under gravity alone, it would take a very long time for
short journeys and longer for long ones (see point one), so you'd be
wise to power (and brake) your train like a regular one.
However, I'm pretty sure it would be quicker, for a given energy input,
than a train travelling on the surface, so it's not totally without
merit.

Well done! Thank you very much for professional templates and community edition

Sounds great! What limitations exist for passengers in regard to age and health issues? What security measures may need to be taken in the current political climate? Hope it's not the TSA (Totally Silly Agency)!

Pity that I may not be around long enough to take a trip! I do love travel, but do not enjoy flying!