Here's some counterintuitive food for thought... communities with higher mixed use denisty demonstrated reduced congestion.
Excerpt:
"[The study] found that roadways in more compact, mixed, multi-modal communities tend to be less congested. This results from the lower vehicle trip generation, particularly for local errands, more walking and public transit travel, and because the more connected street networks offer more route options so traffic is less concentrated on a few urban arterials. This contradicts our earlier assumptions."