The authors provide an explanation of urban sprawl using topics commonly taught in the principles of economics course. Specifically, employing the concepts of congestible public goods, they explain that underpriced road usage leads to an inefficiently large proportion of the population moving farther from the cities. Increased demand for highway usage leads to expansion of the roads, according to common public policy, which reduces the price of using the road even lower than its already inefficient price. Given time to adjust to the lower price of travel, peak demand becomes more elastic and drivers shift away from the inconvenient off-peak to the now relatively cheaper peak alternative. Furthermore, there is complementarity between highways and other trunk-line public utilities. The under pricing of these congestible goods results in an increased demand for their complement: highway usage.