Last week, the Texas Transportation Institute released its big annual study of traffic across the country, the Urban Mobility Report (pdf), which ranks the traffic congestion and commutes of every major city in America.

By their count, Portland has the 23rd worst commute in the nation, with drivers delayed an average of 36 hours per year thanks to traffic.

The report has some interesting and worthwhile data, like seeing how much gas and time is wasted because of traffic jams, but Portland economist Joe Cortright shows some serious flaws in their rankings. His group, CEOS for Cities notes that the traffic rankings don't account for the length of time people actually spend driving, but just rank based on delays. That means cities that sprawl get good rankings, whereas more compact cities are dinged for density.

"For example, consider Nashville and Portland," writes Cortright. According to the report, Portland has a worse traffic problem than Nashville, with and 36 hours of delay per year per traveler, compared to Nashville, which has an average 35 hours of delay. But the data also shows that the drivers in Nashville have to drive farther to get to their destinations and wind up spending a total of 268 hours per year commuting compared to the average Portland commuter who travels only 193 hours per year. The report "completely misses the importance of land use planning as a key to reducing the burden of peak period travel," concludes Cortright.

This is a big deal, because congestion is used as an excuse to build more and larger freeways, when a solution to actually cut down on time wasted in traffic is to build denser cities.