Ken W2KB wrote:As early as the 1960's, or even earlier, science fiction literature postulated a pneumatic tube between NYC and SF. The capsule/trains would "fall" into a downward sloping tunnel, assisted by high speed airflow, and reach speeds of 1,000 mph or so. (No supersonic shockwaves as the internal tunnel flow would be at that speed.)
If anything is ever constructed, the pnematic concept is probably the most feasible.
What could be called the 21st century variant of those pneumatic tube concepts would be the similar concepts for a maglev operated in a partially evacuated vacuum tube. These vehicles would be familiar to anyone who saw the Extreme Engineering show on Discovery featuring the extremely far fetched (and poorly thought out) Trans-Atlantic Tunnel. That show proposed maglevs moving through a floated tunnel at upwards of 1000mph between New York and London. There also was a plan in Switzerland for a series of vacuum maglevs linking the major cities both within Switzerland and potentially in adjacent countries. In so mountainous a country, where any true high speed line is bound to involve a very high proportion of tunnel construction it really does make some sense to make the line fully underground and remove the air from those tunnels to achieve speeds which a surface line would not be capable of. The system was to be called SwissMetro, but it'd seem that despite some testing, the plan has been downgraded and is highly unlikely to be started anytime soon. Certainly
the website has lost much of its
former glory, and the
wikipedia article on the subject makes clear that little will be done in the future on the matter.
If we ever come to a point where it's much more efficient for long distance transportation to use a ground based, perhaps alternative fueled, powerplant than a fossil fuel airborne powerplant then it might make sense to invest in a national vacuum maglev system. With a system providing speeds upwards of 600mph with less friction and a cheaper, domestically produced power source it'd certainly have distinct advantages over airliners, but with a massive cost up front. When compared with an above ground train the problems of a sonic boom, track/rail interface and the propensity for for derailments at such high speeds, birdstrikes and other FOD suction, and other problems are mitigated, as jtr1962 noted. As he also said an inductive pickup would certainly be needed, as a pantograph or shoe would simply break off at the slightest kink in the power supply rail or wire. When compared to the non-maglev pneumatic tube of the 1960s the friction which an airtight seal would require would be unnecessary, and most of the tubes coud have their vacuum maintained, eliminating the inefficient cycling of air a pnuematically driven vehicle would require.
Maybe some day when automation reduces the cost of tunnel construction and fuel costs reach an excessive amount we'll finally reach the point where it makes sense to build tunnels for very high speed ground transportation. However I don't put much faith in this. Oil prices are significantly higher than they were just 5 years ago and they've long since passed points which were previously forecast to trigger reductions in consumption with no action being taken on our part. If we haven't made a significant effort to build TGV or ICE-like HSRs to connect cities like San Fran and LA, or Dallas, Houston, and San Antonio, at 25 to 50 million dollars a mile, with the current oil price problems it'd have to go extremely high for a 100+ million dollar a mile SwissMetro-like tunnel vacuum maglev to make economic sense.