Your first paragraph is nonsense. The problem can be boiled down to the cost benefit structure of roads. There are no congestion charges so the cost is zero or

Your first paragraph is nonsense. The problem can be boiled down to the cost benefit structure of roads. There are no congestion charges so the cost is zero or almost zero plus the time spent driving. Cities build roads where people want to go so the idea that someone would build a useless road should be thrown out. This means the benefits of a constructed road are on average positive. Positive benefits minus zero costs mean infinite demand or as others affectionately call it "induced demand". The only cost that remains that stops people is the fact that they still have to spend time driving so from the drivers perspective the cost benefit structure does not change no matter how much road capacity you build. If their time budget for driving is thirty minutes then the road will fill up until the trip takes longer than thirty minutes. This filling up effect can take the form of people switching from other modes of transportation like buses or bicycles to cars or from smaller cars to bigger cars that take up more space.