Skip to main content
Find a Lawyer

Tracking Every Move You Make, Part Two:
Government Monitoring of Drivers' Cell Phones Raises Some Privacy Concerns that Can Be Easily Mitigated


Wednesday, Oct. 19, 2005

In Kansas City, Missouri, drivers' cell phones may soon be monitored, in real time, to track traffic patterns as drivers pass by one cell phone tower, and move to another. The monitoring can occur even when even when drivers are not chatting, for signals are still being sent to cell phone towers. (Cell phone companies track their users' movements in order to know where to route a given call.)

The purpose of the monitoring, according to the Missouri Department of Transportation (MDOT), is to gauge the way traffic moves along 5,500 miles of the state's roads. In an attempt to reduce traffic congestion, MDOT - working with a private contractor - will put the various cell phones locations onto maps; check traffic speed and congestion points; and then quickly update electronic traffic signs with new congestion alerts. (In the future, if drivers register or subscribe, they might some day be able to receive text messages sent to their cell phones or PDAs, too.) According to news reports, the cost of this form of tracking will be a fraction of the cost of putting traffic flow sensors in the pavement or installing traffic cameras.

MDOT claims that drivers' identities will not be linked to their movements: A spokesperson said, "We care that a cell phone has moved from point A to point B; we don't care that Joel Blobaum's cell phone moved -- that data remain anonymous." Still, since cell phones have unique serial numbers, MDOT could, in theory, change its mind on this point at any time.

MDOT's plan also raises another risk: It contemplates that the private contractor will market information to the private sector - car manufacturers that offer onboard navigation systems, cell phone companies, trucking or other freight businesses or even radio stations that have rush-hour traffic reports. Here, too, there might be a temptation to de-anonymize.

In this column, I will argue that such monitoring - as well as similar monitoring by traffic cameras -- should only be used when drivers are given fair notice and the monitoring agency promulgates to the public a clearly defined statement of its privacy practices. With such safeguards in place, cell phone monitoring provides a useful public function - monitoring increased traffic congestion as Americans continue to use cars and clog roadways. Also, cities and states should consider monitoring systems that do not pose this type of privacy risk, as San Francisco has done.

Distinct from GPS Monitoring, MDOT's Monitoring Uses Cell Phone Towers

Governments have had the ability to measure traffic volume and speed for some time. They can embed sensors in pavement, or mount scanners and cameras on the roadside. But other monitoring methods require the deployment of high cost equipment, which must then be serviced. And cameras can only take photos of limited stretches of road. Cellphones, in contrast, are serviced through their owners, at no cost to the government, and can be tracked wherever a tower is close by.

(The majority of new cell phones come equipped with global positioning system (GPS) devices that can pinpoint drivers' locations more precisely than the tower-to-tower method the MDOT is using. The FCC has required GPS for new cell phones so that emergency services can pinpoint the location of a 911 caller. But GPS is separate from the MDOT system. In theory, two-way pagers could also be used for similar monitoring, but they, too, are not part of the MDOT system.)

MDOT's tower-to-tower method is not new. In 1999, the Washington Post reported that Virginia and Maryland had partnered with a cell phone carrier to track traffic patterns by monitoring cell phone usage on roadways. The two states tested the technology on a 15-mile stretch of the Beltway, between the Springfield interchange and Route 5.

But then, drivers had to actually be chatting on the phone in order for their movements to be traced. In 2005, this is no longer the case - which is fortunate, as we have learned much since then about the risks of driving while using a cell phone.

Recently, transportation officials in Baltimore have used cell phone monitoring, although the data collected has not been relayed to drivers directly by highway signs and the like. Additional projects are underway in Virginia and Georgia. News reports indicate that similar tests have been conducted in Canada. The Missouri project is on a grander scale than these, however: Its plan is to monitor statewide, including rural areas.

In a more academic setting, MIT researchers with the Mobile Landscape Projects have mapped a city based on cell phone usage. Using call origin and destination data, the MIT group is able to reverse-engineer a topographic map of a city's geography and landscape, and of phone usage. . The research is likely to lead to important applications in law enforcement, emergency management, as well as traffic management.

Privacy Concerns: The Risk of Warrantless Searches

Privacy experts worry that the temptation to de-anonymize traffic monitoring will be too strong - and that cell phones and drivers will ultimately be linked, perhaps in an attempt to catch speeders or criminals on the run without the warrant the Constitution requires.

In a previous column, I noted that with proper notice to drivers, it would be appropriate in some circumstances for rental car companies to monitor a driver's speeding and driving patterns using GPS technology placed in the rental car. I noted that this was a contractual matter between two private parties - the rental car company and the driver--with the driver free to opt out if fair notice is given.

But in the MDOT situation, the government is the one doing the monitoring - and there is no chance to "opt out". There, because the government will be watching us, some fear that it will use data for purposes other than monitoring traffic flow. Whenever the government collects information from us, by reaching into our private lives, there is a fear that the Fourth Amendment of the U.S Constitution is being circumvented, or simply violated - because the government is "searching us" without a warrant or our consent.

With the appropriate warrant, such searches can do a lot of good. Law enforcement has successfully traced mobile phone calls to apprehend criminal suspects - for instance, in investigating the Madrid and London terrorist subway bombings.

But will warrants be procured? Or will law enforcement officials claim an "exigency" exception, or the lack of a "search," means such warrants need not ever be gotten?

How to Protect Privacy: Requiring Notice, and Considering San Francisco's Alternative

MDOT needs to alert drivers about its monitoring system. With such notice, drivers and passengers can choose to turn their cell phones off.

Similarly, MDOT needs to have an explicit privacy policy, and set of practices relating to its anonymous monitoring of data.

Armed with this information, it is possible drivers will take the risk - or possible they will press the state to opt for an alternative without the same privacy risks.

And there is an alternative: San Francisco rejected the use of cell phones for monitoring purposes, opting instead to spend around $35 million to install roadside scanners to monitor cars with electronic toll passes. These passes are scanned using Radio Frequency Identification technology (RFID) so that a driver can drive through tollbooth without stopping. When used at tollbooths, the RFID scanner can identify a driver's license plate. The traffic-related scanners in the Bay Area capture anonymous and encrypted information that is destroyed daily.

Why is toll pass traffic monitoring possibly better? The Bay Area model offers an opt-out: Don't get an electronic pass. Or get one, and put it in a metal bag when not in use; the regional transportation authority for the Bay Area mailed metal bags to drivers for just this purpose.

Although drivers would need to take the pass out when approaching a tool booth, they had the option to cloak their pass while on the open roads.

Cell phone users may be able to accomplish the same thing by turning off their phones - but at the cost of not receiving what might be important calls from spouses, children, elderly relatives and others. Putting one's e-pass in a metal bag does not have this downside

Anita Ramasastry is an Associate Professor of Law at the University of Washington School of Law in Seattle and a Director of the Shidler Center for Law, Commerce & Technology. Her other columns on privacy, surveillance, and other issues are included in the archive of her columns on this site.

Was this helpful?

Copied to clipboard