Okay, maybe dense cities were a bad example. Obviously density makes a larger number of stores per square mile more viable than it would be in a less dense area

Okay, maybe dense cities were a bad example. Obviously density makes a larger number of stores per square mile more viable than it would be in a less dense area, even if you have a highly effective transportation system. My point though is that, all factors considered, our current city layout actually is close to optimal under the assumption that road construction is free. The problem of course being that road construction is _not_ free; we've just created an incentive structure that causes the market to behave as it it were.