The Two (Cell) Towers Revisited
Posted by K.M. Das
In the largest such project in the world, the Missouri Department of Transportation (“MODOT”) is in talks with Delcan.NET to implement a statewide traffic monitoring system based on tracking cell phones. The basic idea behind the project is that by tracking specific cell phones as their signal moves from cell tower to cell tower, and overlaying that with highway maps, it will be possible to track how fast or slow traffic is moving. Delcan.NET is already providing this service in Baltimore, on a trial basis, by tracking a 1,000 Cingular users. Delcan.NET and MODOT are expected to finalize the contract within a few weeks and the project is expected to be implemented within six months of that.
Although cell phones have built-in global positioning satellite (“GPS”) technology, the Missouri project will not rely on that technology to track cell phones. Instead, it will rely on the signals that cell phones send to cell towers to allow service providers to route calls. While most cell phones allow users to turn off the built-in GPS tracker, cell phones will not work unless they communicate with the cell towers. Hence, as long as the cell phone users have their phones on, they will be participants in the project. There is no information available at either the MODOT website or the Delcan.NET website that indicates whether cell phone users will be able to opt out of this project. Neither the Delcan.NET website nor the Maryland Department of Transportation website indicates whether the 1,000 Cingular users being tracked in the pilot project in Baltimore were voluntary participants in (or at least allowed to opt out from) the project.
Both the MODOT and Delcan.NET emphasize that the information that they will collect is anonymous. However, because cell phones transmit a unique serial number, along with their call number and a code that indicates their service provider, it is hard to see how this information is truly anonymous. Because of this concern about anonymity, the San Francisco Metropolitan Transportation Commission opted not to rely on cell phone data to track traffic flow. Instead, it relies on electronic toll passes and the data is encrypted and destroyed daily. Despite these advantages over tracking cell phone data, the MTC mailed 250,000 metal bags into which Bay Area drivers can place their toll passes to prevent their passes from being monitored.
Because both the Missouri Department of Transportation and the Bay Area projects base their traffic flow maps on the speeds that individual drivers are moving, whether by tracking how fast their cell phone is moving from tower to tower or their electronic passes are moving from toll booth to toll both, these projects make it possible to local law enforcement authorities to issue traffic tickets to speeders based on their average speed. (The Mean Value Theorem from high-school calculus tells us that if the driver’s average speed was 70 mph between two cell towers then she must have been driving at 70 mph at some point between those two cell towers.)
Further commentary on this topic from Daniel J. Solove here and here.