How's the Dubai to Abu Dhabi Hyperloop coming? That's the ideal situation. Flat route across desert. Government cooperation. Parties willing to pay for an expensive luxury system. If that doesn't work out, nothing will.
I agree. An evacuated tube build in a flat area with little development between the source and destination would really be a great proof of concept if they could get it built and running.
Real tunnels are much more complicated than pretty pictures of tunnels. Many tunnels have to hold up what's above them; they're really long arch bridges. Brunel's Thames tunnel looks like one.[1] Modern tunnels are usually round tubes, but structurally still arches.
Water is a big problem. On a good day, the New York City subway system pumps out 13 million gallons. There are bad days. Many cities are near sea or river level, so plan on a lot of pumping for urban tunnels. Water during construction has been the cause of many tunneling disasters. Some of Japan's longer tunnels hit underground rivers. Tunneling in soft wet soil is mostly about keeping water out.
Tunnels which carry large numbers of people need extensive rescue facilities. Usually, there are two tunnels, with cross-connections and emergency access points. Fire suppression and smoke control systems are needed. Eurotunnel has had five fires, three of them major, despite elaborate fire control systems and much advance preparation for emergencies.
The various Hyperloop documents gloss over all of these real-world issues.
