If highways are always flowing smoothly (green) in rush hour, then it simply means there isn't enough demand for the highway.
It could mean a few things:
- The simply isn't enough population to utilize the infrastructure
- The highway simply isn't going where people want to go
- The economy is in a recession thus it's not being utilized as it was supposed to be
- Toll is too expensive (i.e. highway 407) if there is one
- Who knows. The road is haunted? Too many potholes? Too dangerous?
Anyways, none of the reasons are good. Given a healthy economy and population, newly built highways will reach maturity in a few years and be saturated to a point that enough people no longer find the highway attractive hence it caps out. If it doesn't, then it'll just cap at max capacity.