Many young folks interested in improving connectivity between metropolitan regions wonder whether high-speed trains might be the answer. Unfortunately, fast trains are unlikely to be the solution. Here is what I wrote to a student who asked about the feasibility of high-speed rail. High-speed rail may make sense in the northeast corridor of the USA, but not elsewhere. The challenge is having enough density of origins and destinations. You need both, just like with urban transit.
A good portion of this travel market is price sensitive. This is why the new, inexpensive, bus operators are seeing strong demand for medium distance inter-city travel.
Essentially, high-speed rail is a high-cost service that only a small percentage of the market can afford. You need a large higher density corridor for that relatively small niche that can afford it to amount to enough demand to make high-speed rail work.