Privacy SOS

Mass. High Court: License Plate Reader Surveillance Can Trigger Constitutional Protections

Can the cops in Massachusetts use digital surveillance technologies to track every driver’s every movement throughout the state? Not without violating the constitution, says the state’s highest court.

In a series of crucial court rulings culminating in the historic 2018 Supreme Court decision in Carpenter v. United States, courts in the United States have recognized that 21st century electronic surveillance capabilities fundamentally change the balance of power between the people and the government. In Carpenter, the nation’s high court ruled that police cannot search our historical cell phone location information without a warrant—even if the data reveal a person’s movements in public spaces.

Today, in Commonwealth v. McCarthy, the Supreme Judicial Court of Massachusetts applies the logic developed in cell phone location tracking cases like Carpenter to police use of automatic license plate readers. “With enough cameras in enough locations,” the Court says, “the historic location data from an ALPR system in Massachusetts would invade a reasonable expectation of privacy and would constitute a search for constitutional purposes.”

Automated license plate readers (ALPRs) use optical character recognition to automatically translate images of license plates into machine readable text, creating a file of each car that passes by the cameras. Each license plate reader file contains a picture of the car, the time, date, and location of the surveillance capture, and the car’s license plate number. These data are retained in local, state, regional, and federal databases, and shared among police and federal agencies as well as private corporations. One firm, Vigilant Solutions, boasts a license plate reader database containing billions of images and associated metadata. With a large enough database, populated by license plate reader cameras from across a city, state, or region, police and private entities can keep tabs on the real-time and historical movements of millions of people not suspected of any wrongdoing. Effectively, the technology facilitates dragnet surveillance of motorists.

Here in Massachusetts, dozens of police departments maintain their own license plate reader systems, the Massachusetts State Police key among them. It is unknown how many license plate readers the State Police maintain or access, or how many data points officers have at their disposal. According to a policy governing the State Police, it maintains a one-year retention period for the data its own cameras collect.

In Commonwealth v. McCarthy, the State Police used information from four of its license plate readers at two fixed locations to track the movements of Mr. McCarthy to and from Cape Cod. The information from license plate readers on two bridges was used to investigate and ultimately prosecute Mr. McCarthy on drug charges. Mr. McCarthy moved to suppress evidence related to the license plate readers, arguing that the use of the technology to track his visits to Cape Cod, absent a warrant, violated his rights under Article 14 of the Massachusetts Declaration of Rights, the state’s version of the Fourth Amendment to the United States Constitution.

But the record in Mr. McCarthy’s case did not cover the full extent of license plate reader surveillance in Massachusetts. As a result, the only evidence before the Supreme Judicial Court concerned data from two Cape Cod bridges. This snapshot-style surveillance, the Court holds, wasn’t sufficiently sensitive or detailed enough to trigger constitutional protection.

But the Supreme Judicial Court’s opinion today is clear: in a case with more evidence about the extent of license plate reader surveillance in Massachusetts, the result might have been different.

“With enough cameras in enough locations, the historic location data from an ALPR system in Massachusetts would invade a reasonable expectation of privacy and would constitute a search for constitutional purposes. The one-year retention period indicated in the [State Police] retention policy certainly is long enough to warrant constitutional protection,” the Court holds.

Like [cell phone location] data, ALPRs allow the police to reconstruct people’s past movements without knowing in advance who police are looking for, thus granting police access to ‘a category of information otherwise [and previously] unknowable.’ […] Like both [cell phone] and GPS data, ALPRs circumvent traditional constraints on police surveillance power by being cheap (relative to human surveillance) and surreptitious.

Crucially, the opinion considers what kinds of license plate reader surveillance could trigger constitutional protection, noting the importance of both the quantity of cameras and the sensitivity of the locations under surveillance.

“Of course, the constitutional question is not merely an exercise in counting cameras; the analysis should focus, ultimately, on the extent to which a substantial picture of the defendant’s public movements are revealed by the surveillance. For that purpose, where the ALPRs are placed matters too,” the Court explains.

ALPRs near constitutionally sensitive locations — the home, a place of worship, etc. — reveal more of an individual’s life and associations than does an ALPR trained on an interstate highway. A network of ALPRs that surveils every residential side street paints a much more nuanced and invasive picture of a driver’s life and public movements than one limited to major highways that open into innumerable possible destinations. For while no ALPR network is likely to be as detailed in its surveillance as GPS or [cell phone] data, one well may be able to make many of the same inferences from ALPR data that implicate expressive and associative rights.

Crucially, the SJC also says that any evaluation of the constitutionality of license plate reader surveillance mustn’t be based merely on the few data points police and prosecutors use as evidence in a criminal prosecution, but rather on the larger universe of data that the government has amassed or accessed: “In determining whether a reasonable expectation of privacy has been invaded,” the Court holds, “it is not the amount of data that the Commonwealth seeks to admit in evidence that counts, but, rather, the amount of data that the government collects or to which it gains access.”

Ultimately, the Court recognizes that members of the public and law enforcement officers will need additional guidance, and that more specific rules “will come into focus” in future court cases.

But the Commonwealth of Massachusetts doesn’t have to wait for those cases to work themselves through the courts. Lawmakers on Beacon Hill can act to join the long list of states that have passed comprehensive privacy protections for police use of license plate readers. Now that the state’s highest court has said that persistent, pervasive, dragnet surveillance of motorists’ movements would violate the Constitution, the ball is in the legislature’s proverbial court to fill in the details.

© 2020 ACLU of Massachusetts.