Not a new idea but enough to get an argument going
Way back when Digital Equipment Company existed, I was lucky enough to be teamed up with a fantastic crazy engineer called Tom Stockebrand, He designed the Dec Tape drive for the PDP-8 !
With a $2000 grant from MIT we built a 1km vacuum tube in the desert in New Mexico and sent an array of objects down the tube at high speed and managed to reach twice the speed of sound.
The idea was to prove that high speed travel by rail could compete with air travel if the speed was fast enough and the train was long enough as trains have a difficulty with bandwidth in competing with air travel.
The working model was demonstrated at the reform club in London in mid 1985.
Our sponsor Professor Frank Davidson of MIT was commissioned to advise UK and French governments to invest in Macro Engineer or Big is Beautiful engineering.
In those days we debated sending trains from New York to LA in 21 minutes. We would accelerate at 4G for 12.5 minutes half way across the USA (underground in a vacuum tube suspended by magnetic levitation ) - the concept got to designing 4G chairs to allow aged persons to sit in a seat and withstand 4G for such a time!)
Of course the channel tunnel ended up going a lot slower.
Nevertheless why not build a tube connecting the two cities - the distance is almost 350 miles and to do it 30 minutes would require an average speed of 700mph. Now wheres that slide rule?