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Wireless Beltway

Developing such a map is precisely the job of a white Ford E-150 van that regularly cruises a 30-kilometer stretch of the Washington, DC, Beltway, one of the nation’s epicenters of both traffic and talk (60 percent of area residents own cell phones). The van is owned by San Ramon, CA-based U.S.Wireless, a leader in the nascent business of generating traffic information. As the van tools down a congested stretch of I-495 from Springfield, VA, to Andrews Air Force Base, MD, a passenger talks on a cell phone. Every nuance of the signal fingerprints from that conversation is captured by a network of antennas and computers the company has installed on office and industrial rooftops lining the highway.

Then, thanks to a GPS receiver system in the van, each fingerprint is matched with an exact spot on the route. Later, when cars with cell-phone-chatting occupants drive by, the U.S.Wireless computer picks up the fingerprint, finds a match from its database, and-presto-spits out a location. By gauging how the fingerprint
changes over time, the system’s algorithm can calculate direction and speed, too. “Wherever we set up the network, we’ll be able to monitor vehicle density, speed and acceleration, and provide that information to anyone that’s willing to pay us,” says Howard Blank, U.S. Wireless’s vice president of technology.

To help support this grand experiment in cell-phone-signal cartography, the Maryland and Virginia transportation agencies are ponying up a combined $400,000. Initial results are encouraging, says David Lovell, assistant professor of transportation engineering at the University of Maryland, who is evaluating the test for the state of Maryland. The technology “tracks the trajectory of the vehicle continuously, which allows you to get a better feel for the pattern of congestion on the highway” than is provided by magnetic-loop sensors, he says. The test is continuing, but a report assessing its results is not due until December. Lovell says, however, that “everything appears to be working well so far.”

Still, not everyone is convinced by the tests. “It’s really a bizarre way to do this,” says Paul Najarian, director of telecommunications at the Intelligent Transportation Society of America, a research organization based in Washington, DC. “Every time a building comes up or goes down they have to recalibrateit. And the local topography changes according to the seasons. They basically have to run their van through the coverage areas over and over again to keep it all up to date.”

U.S. Wireless officials counter that recalibration costs are trivial compared to loop detector installation and maintenance. But while the company labors to perfect its technology, chief competitor TruePosition of King of Prussia, PA, is developing an alternative approach that never needs recalibration. TruePosition’s scheme is based on triangulation-determining cell-phone location from the times it takes signals to reach three or more stations. By also analyzing the angle at which a signal arrives, the company can accomplish this feat using just two towers, says Matthew Ward, TruePosition’s manager of strategic product development. Speed is calculated from changes in location over time, as with the U.S. Wireless technology. TruePosition is currently focusing on providing technology for 911 phone-finding. But Ward says the company plans to test its technology for traffic applications.

Beyond cell phones, there’s another wireless technology already beefing up traffic reports in some areas: those increasingly common toll-paying, windshield-mounted radio tags. Normally, a special tollbooth “tag reader” senses the passing device, records the code number associated with the owner’s account and subtracts the toll-and that’s it. But the E-ZPass tags used by more than four million New York-area drivers now double as speed and traffic detectors.

To use the tags for this new purpose, the Transcom coalition of regional transportation agencies mounts readers at regular intervals (ranging from 0.4 to 2.4 kilometers) along a highway. By analyzing the time it takes for a tagged car to pass between the readers, special software can calculate the speed of traffic along key arteries, with the results displayed in a regional traffic-management center in Jersey City, NJ. Just as Sam Mendoza does in San Antonio, operators publicize any snarls on electronic roadside signs or by alerting the news media. By the end of this year, more than 300 kilometers of highway stretching from Hartford, CT, to Trenton, NJ, will bristle with tag readers for speed detection, with Massachusetts and Pennsylvania eyeing the idea.

Ultimately, it might be possible to complement-or even replace-this growing arsenal of sensors with a third wireless device: the GPS receiver showing up in more and more cars, mainly as a navigation aid (see “The Commuter Computer,” TR June 2000). GPS could, in theory, provide a means of continuously tracking a vehicle’s location. But although traffic planners would love to collect all those rolling position figures and squeeze the numbers for speed and traffic data, it will be hard to pull off, at least for now. That’s because GPS receivers are just that-receivers, which determine position from incoming satellite signals-and don’t send position data unless a driver initiates a link, as when calling police for help or looking for directions. Such calls are relatively rare compared to cell-phone chatter; besides, reading a car’s position would involve eavesdropping on the content of a call rather than just sensing a signal.

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