Traffic Down 30% in Cities: How?

New data show that in 2008 traffic congestion in the nation's cities declined by 30 percent, the result not of new roads or transit, but of modest declines in VMT.

The decline in congestion -- which analysts have labeled 'startling" -- was almost universal. Traffic congestion actually declined in 99 of the nation's 100 largest metro areas, according to Inrix, which monitors traffic around the nation. The company's data come from tens of billions of reports from GPS-equipped vehicles traveling the nation's roads, the same data that provides real-time traffic information to commercial users and web-services like Mapquest, Garmin and On-Star.

Their key conclusions: 'peak hour congestion on the major roads in urban America decreased nearly 30 percent in 2008 versus 2007,' and nationally, 'congestion was lower every hour of every day in 2008 versus 2007 – between 15 percent and 60 percent lower depending on the hour and day.' See the full report here.

How did such a small decline in travel produce such a big drop in congestion?"

Full Story: The Tipping Point



Suspect Study! On closer review of the data...

If you consider the source of the data -- only cars with GPS devices -- you've got to take this study with a very large grain of salt.

This study probably leaves out most cars -- I find it hard to believe that more than a relatively small percentage of cars are equipped with a GPS device. Did the study take this into account? Did the study take into account that there might be a bias built into the study if there is a direct correlation between income and the presence of a GPS device in your car? (I'm betting that folks with higher incomes are more likely to have a GPS device in their vehicle.) Is this sample really representative of the total universe?

Without these details, I'd be mighty reluctant to make any policy decisions based on this suspect study. The full article didn't answer these questions -- and I'm afraid I don't have the time to read the study now. Perhaps it answers these concerns satisfactorily. But these are the questions planners and elected officials should be asking before they give this study any credibility.

Daniel Lauber, AICP
AICP President 2003-2005, 1992-1994
APA President 1985-1986

Yes, Mr. Lauber, if you look closer...

It appears that the researchers deserve more credit than you so quickly give them. Follow the link and I think you'll find that they didn't just recruit drivers who already own ordinary GPS devices.
Mike Stanger

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