Since it's an interesting mindgame I thought about it a little further: There IS a hard problem to solve here: If your train takes 5min to stop from 4000km/h, i

Since it's an interesting mindgame I thought about it a little further: There IS a hard problem to solve here: If your train takes 5min to stop from 4000km/h, its breaking distance would be 166km (assuming linear deceleration)! This means that you could only shut down sectors further away than 166km from the closest train - all sectors within are your vulnerable zone. That seams quite risky to me. On the other hand we do fly millions of people a year in pressure cabins with no way to escape. Since with this new system people's life would depend on tubes 160km long instead of 70m (length of a 747), all you need is materials that are 2000 times more reliable than those of our jet planes. While being emerged in seawater. And enduring a much higher pressure difference. Yeah. I'd say let's wait and see what nanotechnology gives us :).