"Smart growth" responsible for greater traffic congestion than sprawl

[John Zeger]

Being curious about the differences in the impact of growth through densification compared to growth by geographical expansion on traffic congestion, I used some data that was organized by Wendell Cox on major U.S. cities to do an analysis. I first looked at those cities that gained at least 10 percent population between 1990 and 2000 for which traffic congestion figures had been collected by the Texas Transportation Commission. I came up with 12 such cities. I then grouped these cities into three categories -- those that grew primarily through expansion, those that grew primarily through increasing urban densities, and those that grew by both expansion and densification. In the first group I put Charlotte, NC; Charleston, SC; and Columbus, OH. In the second group I put Dallas, TX; Jacksonville, FL; Portland, OR and San Diego, CA. In the final group I put Las Vegas, NV; Austin, TX; Pheonix, AZ; Winston-Salem, NC; and Houston, TX. The average increase in traffic congestion measured in terms of increase in travel time for the expansion group was 11.0%, the average for the densification group was 20.5%, and the average for the combined group was 12.9%.

The conclusion that can be reached from this analysis is that urban population growth causes an increase in traffic congestion and that growth by increasing densities ("smart growth") results in greater traffic congestion than does growth through land expansion. It is worth noting that all four "smart growth" cities examined (Dallas, Jacksonville, Portland, and San Diego) have commuter rail systems. So the presence of commuter rail did not prevent an increase in traffic congestion in those cities.

[Rando]

That's great research. I'm surprised that your post is still up & not yanked down. There is like a conspiracy to cram & jam people onto the existing 2.7% of the currently urbanized U.S.

It should be common sense that with higher density there is more congestion. There is not really a reduction in VMTs. Somehow many people think: more_people=less_traffic. Ridiculous math.

I've done similar research. One thing was to get a driving density of VMT/square_miles. Of course it goes up considerably with population density.

Also correlated are urban population size & density the larger. So the smaller metros, say <500,000, are fairly low density & really sprawl, but most metros of over 3 million will be considerably denser, but thought to sprawl more because of the high population count.

The densest urban area is LA; so it has the least sprawl & 12+ million people. The NYC urban area is about #4 for density. SF Bay is #2. The LA area is also pretty low on freeway lane miles per capita. Kansas City & Ok City are pretty low in population density & have great travel times.

Many people think Cox & O'toole are biases & maybe even twist facts. Not true. I've verified some of their facts with the Census & the TTI. Try the Texas Transportation Institute; They have all sorts of data.

Common sense? Fewer people in a square mile=less traffic.