yael perkal

But, if there is less air then there is less friction and less heat. I think that the tunnels should have heat absorbent, natural source is better like flow of water.

This is interesting.

Thank you, I assumed somebody have already thought about it before, as it very simple concept. Thank you all, I really like this forum

What do you think about building sealed long tunnels for trains, that after they are being built, there are pumps vacuuming it out of air, at high percentages of the atmospheric density. Suppose the train is sealed too and compressed like airplanes, and there are sealed passages in the stations connecting the train to to open world, to let people get in and out of the train. What do you think about reducing drag and fuel consumption in this model?