Sam Jaffe, writing on the Navigant Research blog, says... "The biggest concern with this plan has to do with temperature. The pod will be compressing air and expelling it downwards and backwards. All that air compression creates an enormous amount of heat, which can damage the pod and its machinery"....I remember those pneumatic tubes in department stores...
Musk's idea isn't new. Ever since pneumatic tubes using negative air pressure to shoot capsules through tubes showed up decades ago -- department stores used them for transactions and newspapers used them to carry stories from the newsroom to operators that would produce metal type for the printing presses -- people have dreamed of traveling through cylinders at high speed.
Imagine traveling like that.
I believe the truly modern technological solution is not to travel at all. Overcome the need to have the body go anywhere. That's the most efficient answer to our transportation problems. Musk's tube would supposedly get people back and forth between San Francisco and Los Angeles. Why? Pick a city. Stop this senseless flitting from one city to another.