If you are ever in London, this place is amazing:
<a href="https://www.postalmuseum.org/visit-us/what-to-expect/mail-rail/" rel="nofollow">https://www.postalmuseum.org/visit-us/what-to-expect/mail-ra...</a>
All the problems from the hyper loop involve the energy of a vacuum. Why not accelerate the air in the tube in an actual loop? You reduce air pressure in front and increase it behind the car? Train cards could have baffles to allow for stops (let the air pass by the car).
The images don’t appear for me but do on the original New Statesman article:<p><a href="https://www.newstatesman.com/politics/2013/12/londons-victorian-hyperloop-forgotten-pneumatic-railway-beneath-capitals-street" rel="nofollow">https://www.newstatesman.com/politics/2013/12/londons-victor...</a>