Thanks for your comment. There are several corridors in the US where high-speed rail was or is being considered.
The emissions per passenger mile depend very much on occupancy, as well as the carbon intensity of power generation. Also, putting in place the infrastructure for high-speed rail is very energy-intensive (making all that concrete).
Here is a good study of the relative impact of flying, high-speed rail, and driving. http://iopscience.iop.org/1748-9326/5/1/014003/pdf/1748-9326_5_1_014003.pdf
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