But it's not just density that helps reduce car use. In fact, the study fond that mix of uses has more of an impact on reducing car use than density.
"Planners for the last 40 years have been calling for mixed-use development, but we haven't known how beneficial mixed-use development was in terms of discouraging driving and encouraging walking and transit use. The study provides an estimate [of] just how important it is to balance jobs and housing in a neighborhood, rather than having all housing or all jobs.
The study made an attempt to generalize across something like 60 individual studies. It provides measures that can be used by planners and by policy makers to evaluate development proposals, to do health impact assessments, to do climate action plans.
If California metropolitan areas, under their smart growth climate law, double the density of their regions over the next 20 years, what effect will that have on total vehicle miles and total emissions? Now there's a convenient way of summarizing the effects. We can say with some certainty that if you double density you'll get a five to 10 percent reduction in vehicle miles traveled."