Yesterday there was a post on here where Elon tweeted a reply to someone that his guess was the closest yet:<p><a href="https://news.ycombinator.com/item?id=6046943" rel="nofollow">https://news.ycombinator.com/item?id=6046943</a><p>He seems to verify that there will be "pods" 2m wide, so it sounds like this will be tunnel- or tube-based.
The real issue is the safety issue. Shutting down a vehicle moving at 2500 feet/sec without subjecting the occupants to unhealthy G-forces is going to be rather difficult. But who knows, the human body can certainly withstand some pretty intense shock:
<a href="http://www.youtube.com/watch?v=s4tuvOer_GI" rel="nofollow">http://www.youtube.com/watch?v=s4tuvOer_GI</a>
If it's any kind of open track, it'll have problems with sonic booms. 400 miles in 30 minutes is 800 mph, a speed which exceeds the speed of sound at sea-level (~ 760mph). The neighbors aren't going to like that.