TTI’s Urban Mobility Report Is Still Only About Mobility

Traffic

Evaluating land use and transportation policies in terms of accessibility rather than mobility is the goal of many planners and advocates, whether they know the terminology or not.  This new focus requires recognizing the interconnectedness of land use and transportation decisions.

Unfortunately, one of the most influential voices in transportation research and policy has not yet made these changes.  From Greater Greater Washington (via Market Urbanism):

The Texas Transportation Institute today released the final version of their report on congestion, which ranks the DC area tied for first with Chicago in hours wasted in traffic. Unfortunately, the report’s methodology completely misleads as to the seriousness of traffic, and TTI is pushing the wrong policy solutions.

The TTI report narrowly looks at only one factor: how fast traffic moves. Consider two hypothetical cities. In Denseopolis, people live within 2 miles of work on average, but the roads are fairly clogged and drivers can only go about 20 miles per hour. However, it only takes an average of 6 minutes to get to work, which isn’t bad.

On the other hand, in Sprawlville, people live about 30 miles from work on average, but there are lots and lots of fast-moving freeways, so people can drive 60 mph. That means it takes 30 minutes to get to work.

Which city is more congested? By TTI’s methods, it’s Denseopolis. But it’s the people of Sprawlville who spend more time commuting, and thus have less time to be with their families and for recreation.

Sadly, despite CEOs for Cities pointing out these methodological problems last year, TTI went ahead and finalized its report without fixing them (PDFs). TTI ranks Portland as worse than Nashville, with a Travel Time Index (TTI) of 1.23 1.15 for Nashville and 1.151.23 for Portland. However, because of greater sprawl, Nashville commuters spend an average of 268 hours per year commuting, while the average Portland commuter spends 193 hours per year.

What does this mean for public policy and the Washington region? TTI’s data is often used to justify spending money on new freeway capacity, since congestion sounds bad. TTI even promotes this approach. Tim Lomax, a co-author of the report, told the Post’s Ashley Halsey III, “You can do little things like stagger work hours, fix traffic-light timing and clear wrecks faster, but in the end, there’s a need for more capacity.”

In some sense, we shouldn’t be surprised, since the report is titled the Urban Mobility Report.  However, the goal of commentators and the CEOs For Cities report is to call attention to the fact that mobility (or level of congestion) alone is not an adequate means of measuring the performance of our land use and transportation systems.

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