KM - I was encouraging you explain your reasoning in engineering terms. Faster, cleaner, safer than what? All three at once? Clearly the train is not faster than air travel. Regarding building in the near term: the OP allowed for a tunnel. I am unaware of any technical reason the Strait could not be crossed with a tunnel using today's technology, given it amounts to only two English Channel tunnels.
Actually, I was referring to faster than air travel. There have been some references (going back many years) to travel through evacuated tubes at speeds of over 1000 mph (1600 kph), and with continued advances in maglev technology, etc., this should become feasible. I was careful to point out that it is not an economically logical concept today, but in the future (twenty second century maybe) there is no reason to assume that it won't be.