The east coast and west coast states between them, however, have over half of the US's population and are mostly relatively dense. Transcontinental passenger service might be a little pointless, but clearly there is room for good-quality high speed lines. SF to Seattle, say, would be doable non-stop in about four hours on top-quality conventional (ie ~320km/h) rail. Less with high-speed maglev and other exotics, but now that China seems to have largely lost interest, I'm not sure if anyone is seriously pursuing those.