The real answer is that most roads are a transient solution as transit gets built out. They should form an auxiliary network, not the backbone of a country's transportation.

China also had a couple of twists. At least parts of the West have general counterparts to these problems.

Some cities had infrastructure built out ahead of demand. Many of the cities did start filling up with people, which is great. However, the infrastructure aged well ahead of when it was used. So some of the infrastructure is coming due for expensive maintenance, often without a solid tax structure to pay for it. Readers of Strong Towns will recognize this general pattern of overbuilding without building a solid foundation, but it just has a Chinese character to it.

Linked to that is a growing debt crisis at the local government level. The most current estimate I could find is 94 trillion yen (US$13 trillion). Many infrastructure investments were made that are projected to never be paid off in their lifespan. Again, Strong Town readers will recognize this general pattern.

Going from pure speculation, I wonder whether they might have been able to avoid some of the problems with aging unused infrastructure by setting aside land and right-of-way. Here in Portland, when they were planning the I-205 freeway, one concession to transit and bike advocates was to set aside a right-of-way for a transit way and a bike path. That particular concession was made around 1975. The bike path was built immediately. The northern end was used to extend the preexisting light rail to the airport on September 10, 2001 (great timing) as part of the Red Line. The southern end became part of the Green Line later.