> a single line, over a relatively short distance, through terrain that isn't too challenging, going at moderate speeds,

None of this is true, or remarkable.

Almost all high-speed rail lines are a single line.

This line would have been 520 miles, or about 800km. That's longer than almost every high speed rail line in the world. For point of reference, all high speed rail in the UK put together is 1,377km. All high speed rail in Japan is 2,760km. While this single line would not be close to the world's longest (China has a single high speed rail line of nearly 2300km), it's about 30% of the total length of all Japanese high-speed lines put together.

This line was planned to have a max speed of 220mph, which is faster than all but one system in the world.