Japan's railroad system has a big geographic advantage - the country is long and narrow. The railroad system is primarily a long end to end line with short crosswise branches.[1]
That's an efficient structure. The branch lines don't have to be fast. Many are still narrow gauge, at 3 ft 6 in.
The US had to fill a huge area in the railroad era. That left a lot of underutilized track once the road network got good.
The US had to fill a huge area in the railroad era. That left a lot of underutilized track once the road network got good.
[1] https://www.jrailpass.com/pdf/maps/JRP_japan.pdf