Commuting. Suburbs are, generally, huge collections of roads that are ready for children to play on, so they're going to be relatively narrow roads, like 2-2.5

Commuting. Suburbs are, generally, huge collections of roads that are ready for children to play on, so they're going to be relatively narrow roads, like 2-2.5 cars wide. You have that kind of roadwork for multiple square miles. All those people need to go to and from work, and so that's increased traffic. The larger the suburb, the further people need to go to get food, the longer they'll be on the road, the more cars will be on the road concurrently (most traffic in long commute times is going the whole length of the slow commute time because everyone lives further away)