Driving to work, you notice the traffic beginning to slow. And because you have your cell phone on, the government senses the delay, too.
A congestion alert is issued, automatically updating electronic road signs and Web sites and dispatching text messages to mobile phones and auto dashboards.
In what would be the largest project of its kind, the Missouri Department of Transportation is finalizing a contract to monitor thousands of cell phones, using their movements to map real-time traffic conditions statewide on all 5,500 miles of major roads.
It is just one of a number of initiatives to more intelligently manage traffic flow through wireless data collection.
Officials say there is no Big Brother agenda in the Missouri project: The data will remain anonymous, leaving no possibility to track specific people from their driveway to their destination.
But privacy advocates are uneasy nonetheless.
"Even though it's anonymous, it's still ominous," said Daniel J. Solove, a law professor at George Washington University and author of "The Digital Person." "It troubles me because it does show this movement toward using a technology to track people."
Cell phone monitoring is already being used by transportation officials in Baltimore, though not yet to relay traffic conditions to the public. Similar projects are getting underway in Norfolk and a stretch of Interstate 75 between Atlanta and Macon, Ga.
But the Missouri project is by far the most aggressive -- tracking wireless phones across the whole state, including in rural areas with lower traffic counts, and for the explicit purpose of relaying the information to other travelers.
In fact, it would be the biggest system of its kind in the world, said Richard Mudge, a vice president at Delcan Inc., the U.S. unit of the Canadian company that won the Missouri bid.
The contract is expected to be completed within several weeks -- with a cell phone monitoring system tested and implemented within six months after that. The cell phone provider for Missouri has not been disclosed, but Delcan uses data from Cingular Wireless LLC phones in the Baltimore project.
Governments have had the ability to measure traffic volumes and speeds for years. They can embed sensors in pavement, or mount scanners and cameras along roads. But those monitoring methods require the installation of equipment, which must be maintained, and can take only a snapshot of traffic at a particular spot.
In contrast, "almost everyone has a cell phone, so you have a lot of potential data points, and you can track data almost anywhere on the whole [road] system," said Valerie Briggs, program manager for transportation operations at the American Association of State Highway and Transportation Officials.
Although most new cell phones come equipped with Global Positioning System capabilities that can pinpoint their exact locations, the tracking technology used for transportation agencies does not depend on GPS.
Instead, it takes the frequent signals that wireless phones send to towers and follows the movement of the phones from one tower to another. Then it overlays that data with highway maps to determine where the phones are and how fast they are moving. Lumping thousands of those signals together can indicate traffic flow.
A Delcan demonstration Web site developed for Baltimore uses various shades of green, yellow and red to show block-by-block whether vehicles are moving at or below the speed limits. As rush hour started on a recent work day, observers could watch as green turned to yellow and then to red on roads heading out of downtown.
The Baltimore project began this spring as a pilot program that monitors Cingular users over about 1,000 miles of roads, but Maryland officials hope to eventually create a statewide version. (A Delcan competitor, Atlanta-based AirSage Inc., has an agreement with Sprint Nextel Corp. to monitor phones for its projects in Georgia and Virginia.)
Pete Rahn, director of the Missouri Department of Transportation, would like to make a similar Web site available to Missouri motorists, and to post estimated travel times on electronic road signs.
The Missouri and Maryland plans also assume that the contractor will market more detailed information to the private sector -- automakers that offer onboard navigation systems, cell phone companies, shipping businesses or news media that broadcast rush-hour traffic reports.
The private sector marketing helps drive down the states' cost. Missouri expects to spend less than $3 million a year on the service, Rahn said, although the exact price will not be known until the contract is finalized.
Maryland is spending $1.9 million, although the entire Baltimore project costs nearly $5.6 million, said Mike Zezeski, director of real-time traffic operations for the Maryland Department of Transportation.
By contrast, the San Francisco Bay Area spent about $35 million over several years to install roadside scanners and to develop computer programs, Web sites and call centers for a real-time traffic service based on electronic toll passes, said Randy Rentschler, a spokesman for the region's Metropolitan Transportation Commission.
Officials considered using cell phone monitoring but opted against it, partly because of privacy concerns.
As with cell-phone monitoring, the information received from the Bay Area's toll scanners is anonymous. It is also encrypted and destroyed daily. But the local transportation commission went a step further, mailing 250,000 metal bags into which motorists could place their toll devices to prevent them from being monitored on the roads.
Cell phone users can accomplish the same thing by turning off their phones.
The Electronic Privacy Information Center (EPIC) in Washington suggests that cell phone owners should be notified that their phones are being monitored for traffic data.
Privacy experts also worry that the traffic monitoring could later evolve into other uses -- perhaps to catch speeders or fugitives.
That is because each cell phone has a unique serial number, in addition to its call number, and a code that indicates its service provider. A cell phone company must always be able to track the location of its phones to know where to route a call.
"It's a mission creep issue that would be of most concern to consumers," said Lillie Coney, associate director of EPIC. "They may start out saying we want to know if there's a traffic problem and then take that information and start using it for different purposes."