Suburbs don't have to be substantially less dense. Heck, I think there are neighborhoods in my nearest city (Pittsburgh) that are less dense than my town just outside of it. Mine was built before cars were a given and when the trolley was a given.
There are "exurbs" which are just abominations of low density and bad design. There are some lower density suburbs, and yeah, neither of those are sustainable.
There are "exurbs" which are just abominations of low density and bad design. There are some lower density suburbs, and yeah, neither of those are sustainable.