Automated License Plate Readers Threaten Our Privacy

Co-Authored with Peter Bibring, Senior Staff Attorney at the ACLU of Southern California

Law enforcement agencies are increasingly using sophisticated cameras, called “automated license plate readers” or ALPR, to scan and record the license plates of millions of cars across the country. These cameras, mounted on top of patrol cars and on city streets, can scan up to 1,800 license plate per minute, day or night, allowing one squad car to record more than 14,000 plates during the course of a single shift.

Photographing a single license plate one time on a public city street may not seem problematic, but when that data is put into a database, combined with other scans of that same plate on other city streets, and stored forever, it can become very revealing. Information about your location over time can show not only where you live and work, but your political and religious beliefs, your social and sexual habits, your visits to the doctor, and your associations with others. And, according to recent research reported in Nature, it’s possible to identify 95% of individuals with as few as four randomly selected geospatial datapoints (location + time), making location data the ultimate biometric identifier.

To better gauge the real threat to privacy posed by ALPR, EFF and the ACLU of Southern California asked LAPD and LASD for information on their systems, including their policies on retaining and sharing information and all the license plate data each department collected over the course of a single week in 2012. After both agencies refused to release most of the records we asked for, we sued. We hope to get access to this data, both to show just how much data the agencies are collecting and how revealing it can be.

ALPRs are often touted as an easy way to find stolen cars — the system checks a scanned plate against a database of stolen or wanted cars and can instantly identify a hit, allowing officers to set up a sting to recover the car and catch the thief.  But even when there’s no match in the database and no reason to think a car is stolen or involved in a crime, police keep the data. According to the LA Weekly, LAPD and LASD together already have collected more than 160 million “data points” (license plates plus time, date, and exact location) in the greater LA area—that’s more than 20 hits for each of the more than 7 million vehicles registered in L.A. County. That’s a ton of data, but it’s not all  — law enforcement officers also have access to private databases containing hundreds of millions of plates and their coordinates collected by “repo” men.

Law enforcement agencies claim that ALPR systems are no different from an officer recording license plate, time and location information by hand. They also argue the data doesn’t warrant any privacy protections because we drive our cars around in public. However, as five justices of the Supreme Court recognized last year in US v. Jones, a case involving GPS tracking, the ease of data collection and the low cost of data storage make technological surveillance solutions such as GPS or ALPR very different from techniques used in the past.

Police are open about their desire to record the movements of every car in case it might one day prove valuable.  In 2008, LAPD Police Chief Charlie Beck (then the agency’s chief of detectives) told GovTech Magazine that ALPRs have “unlimited potential” as an investigative tool.  “It’s always going to be great for the black-and-white to be driving down the street and find stolen cars rolling around . . . . But the real value comes from the long-term investigative uses of being able to track vehicles—where they’ve been and what they've been doing—and tie that to crimes that have occurred or that will occur.”  But amassing data on the movements of law-abiding residents poses a real threat to privacy, while the benefit to public