AMoonHawk saidLOL .... " speeds of up to 4,000 miles per hour" ..... oh sure ... the human body can withstand that for 45 minutes
Actually, it can. The speed itself is not the problem; when you're travelling at constant speed, no net force is applied to your body. It's the acceleration that gives you the 'push'.
Most subway trains accelerate at about 2.5 mph per second. At that rate, it would take about 27 minutes to accelerate from 0 to 4,000 mph. That is too long. So if you would limit the acceleration phase to under 10 min, you would need an acceleration 3 times that of a subway train. That would be very uncomfortable in an actual subway train with its lousy seats, but if you place all seats in the direction of travel and make them comfortable giving good back support, like a plane, I think it would be very well tolerable. Supersportscars accelerate 0-60 in 4 seconds, that is an acceleration of about 15 mph per sec, people can easily withstand that too - although not for 10 minutes probably..