310 mph on Japan Maglev Train

Wired:

It’s currently the world’s longest and fastest stretch of maglev train, reaching speeds as high as 310 mph in a demonstration last week. But Japan’s L-Zero only lives on 26 miles¹ of test track, and we’re still more than a decade away from completion.
After five years of trials, plus some starts and stops, Central Japan Railway Co. is finally starting construction on a maglev line between Nagoya and Tokyo, a 177-mile trip that will be cut from 95 minutes on today’s high-speed trains to just 40 minutes with maglev by 2027. To put that kind of speed in perspective, Amtrak’s Acela takes about 3 hours and 40 minutes to go about 210 miles. A trip from Boston to New York on maglev would take under an hour.
By 2045, JR Central hopes to extend the line to Osaka, which will cut the number of passengers on the frequent flights between the two cities. When built, the maglev will join an airport line in Shanghai and a low-speed train in Nagoya, among other rail systems that use magnets to float rail cars above a track to reduce friction and increase stability.
While Japan’s maglev promises to be an impressive technical feat, there’s some worry that Japan’s population won’t be big enough to sustain it. The Nagoya extension alone is expected to cost anywhere from $52 billion to as much as $90 billion, ² thanks to the difficulty of tunneling through cities and mountains to make a straight track.

Problem number one of transportation improvements: how to fit the needs of the design into the built landscape.  It killed many an urban interstate highway route over the years, and any new high speed transport solution is going to run into those issues.