[www.citymetric.com]

I think this guy is channeling Bob2. The term "fast enough" trains seems to be built around trains that can run about 110 mph, with average speed including stops of around 70 mph. IOW, what the NE Regionals achieve (though they can run up to 125 mph in places) and many if not most conventional (non-HSR) passenger lines in Europe. Yes, both the NEC and most European main lines are largely if not completely (for long distances) grade-separated, but they're not up to HSR standard so speeds are somewhat limited.

Between DC and Boston, and on most European lines, electrification is standard to support the higher speeds. Amtrak and the UK have some diesel-powered trains running at top speeds of 110-125 mph, but most are in the 90-100 maximum range. The problem with those diesel trains is not only the lower top speed, but also the more leisurely accel and decel, which cuts into their competitiveness with short-distance air and 2-3 hour driving.

Anyway, Bob has been promoting "fast enough" trains by various names for a long time. Interesting to see somebody actually writing a book that's at least in part about them.