Costs of sprawl

Putting numbers on the obvious: sprawl costs taxpayers more. Canadian study, but ratio matters more than the precise numbers. http://usa.streetsblog.org/2015/03/05/sprawl-costs-the-public-more-than-twice-as-much-as-compact-development/
I'm amused that their low-density urban is near the high end of US cities -- Chicago, Boston -- while the "mid-density" is higher than anything I know of besides NYC. Certainly denser than San Francisco or Somerville.