Rush Hour

Missouri is the latest state to implement a program that measures traffic congestion on major roads based on the average time it takes drivers' cell phone signals to pass from cell tower to cell tower along those roads.

Georgia, Maryland and Virginia have completed limited rollouts in select cities, but in February, Missouri became the first to carry out a statewide implementation, covering 5,500 miles of its busiest roads -- generally interstates and numbered routes.

"Missouri motorists will be better informed than anyone else in the country on which roads to use and how long the drive will take," said Pete Rahn, director of the Missouri Department of Transportation (MoDOT), in a statement.

At a cost of $6.2 million for two years, the cell phone system will provide traffic monitoring at a fraction of traditional method prices, according to MoDOT.

"With this new technology, we'll cover many more miles of highway without any new equipment," Rahn said.

MoDOT estimates that over the long run, cell phone traffic monitoring technology will cost less than one-sixth of traditional traffic detection costs.

The current methods of monitoring traffic on most U.S. highways are strategically placed "stick cameras" and embedded sensors in the pavement, which need regular replacement. The high price of those systems limits how many miles of highway they can track. By contrast, using cellular traffic monitoring technology, a state can constantly tap into a fleet of private vehicles to monitor traffic congestion for entire regions.

Cell phone companies divide cities into several zones, each encompassing roughly 10 square miles. When cell phones are turned on, the company can document the time a user passes from one cell tower to another.

Companies such as Delcan, Missouri's cellular traffic monitoring provider, pay cellular companies for the right to integrate their software with the companies' signal location databases. The software is programmed with a road map of each zone and uses algorithms to guess the route a driver takes and the driver's speed from tower to tower. The average speed of each route is continually recalculated to produce real-time traffic data -- states transmit this information to motorists through color-coded online graphics and electronic road signs.

Richard Mudge, vice president of Delcan, said the state would likely continue using stick cameras and embedded sensors in high-volume areas because the equipment can produce lane-by-lane information.

Maryland has used cellular traffic monitoring for the Baltimore metropolitan area for more than one year. The Maryland Department of Transportation didn't spend a penny of its own money on the project. Maryland used $1.9 million of its allocated funds from the Federal Highway Administration. The state normally would have needed to contribute matching funds to the project to use the federal money, but Delcan made up the difference.

Flexible Privacy

Cell phone signal traffic monitoring technology has spurred criticism from some privacy advocates worried that the technology will lead to normalizing a surveillance infrastructure capable of tracking our every footstep.

Mudge said nobody involved in the project had any interest in, or use for, tracking individuals. He said the software calculating traffic congestion in the cellular companies' databases keeps a cell phone user's identity on the cellular company's side of the firewall, where it is used for billing purposes.

"We don't need it. We don't want it. They wouldn't want to give it to us anyway," Mudge said. "If, for some reason, Maryland came to us and said, 'We'd like to know who was speeding on I-95 yesterday at 3 p.m. -- tell us,' we [wouldn't] know. All of us