It's possible to overbuild roads where there isn't demand for them. But for major metropolitan areas, there are large numbers of people who want to go to simila

It's possible to overbuild roads where there isn't demand for them. But for major metropolitan areas, there are large numbers of people who want to go to similar categories of destinations, and their choice of specific destination is constrained by convenience. If expanding a road reduces congestion (and thus time to reach somewhere), more people will travel farther distances to get there until a new congestion equilibrium is reached.