Everything old is new again.  Partially borrowing a technology
concept used by banks, entrepreneur Elon Musk introduced a
design for a new transportation system that he said could
shuttle passengers between Los Angeles and San Francisco in 30
minutes.  For now, it's an early, conceptual design at best -- a
proposal for an idea that may never be built and likely gone
unnoticed had it not been for the attention Musk receives for
his other projects, including Tesla Motors and PayPal.  "The
Hyperloop (or something similar) is, in my opinion, the right
solution for the specific case of high traffic city pairs that
are less than about 1500 km or 900 miles apart," he wrote on his
blog Monday, following through on his previous hints for the
project.  "Around that inflection point, I suspect that
supersonic air travel ends up being faster and cheaper. However,
for a sub several hundred mile journey, having a supersonic
plane is rather pointless, as you would spend almost all your
time slowly ascending and descending a