[chipsy]

In sprawl, the city is bearing most of the risk: all the developer has to do is throw up some more cookie-cutter detached homes and sell them, while the city has to keep all of the grid infrastructure and services to those homes running for decades to come; low density sucks up the budget that could otherwise be used to create big-ticket service improvements like transit. At the bottom end, this can send suburbs into a Detroit-esque downward spiral where they are no longer viable.

Developers are much more grudging in taking on the economic risks of infill projects with higher densities, but even low-rise, 3-4 story buildings are sufficiently dense to push this equation in the other direction and make city services more sustainable and cost-effective.