Traffic jams don 't stop the data flow

As commuters reach highway on ramps, detectors know all about it

By Peter Korn

The Portland Tribune, Sep 12, 2006, Updated Oct 30, 2009

If you count every vehicle and its speed on every Portland-area highway every minute of the day, and then archive all that information for years, traffic can generate an incredible amount of data.

The people whose job it is to learn something useful from the data work at the Intelligent Transportation Systems Lab at Portland State University. They’re the ones who provided the information for the Portland Tribune’s charts and tables comparing commutes.

Ironically, the PSU lab, run by Robert Bertini, is designed to analyze data produced as a mere byproduct.

During the last two years the Oregon Department of Transportation has placed approximately 150 sensors, called wire loop detectors, beneath Portland-area state highways, most just before the on ramps. The detectors produce a constant data flow by measuring what types of vehicle pass over them and how fast the vehicles are traveling.

But the reason for installing the detectors was not to produce data about traffic. The Transportation Department put the detectors in place so it could better move the traffic around.

One of the most significant traffic managing advances in recent years has been the on-ramp signals that control the rate at which drivers can get on a highway. By stopping commuters at on-ramp red lights, the meters can keep the number of cars on the freeway at a pre-gridlock level. Or, at least, that’s how it’s supposed to work.

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