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How Are Police Departments Using License Plate Reader Data?

The Oakland, Calif., Police Department has released its license plate reader data, which reveals a lot -- but it's tough to understand what it all means.


This Google map created by the Electronic Freedom Foundation of more than 63,000 geographical points shows where and when a license plate was scanned by the Oakland, Calif., Police Department.

Automatic license plate readers (ALPR) have grown in sophistication, and a number of police departments across the nation have adopted the technology. On Jan. 21, the Electronic Frontier Foundation (EFF) released ALPR data it received from the Oakland, Calif., Police Department (OPD). A foundation blog post demonstrates what the ALPR data collected by a police department looks like when mapped, and speculates on what the data might be used for.

EFF Investigative Researcher Dave Maass explained to Government Technology that while his organization finds it difficult to take a stance for or against the technology, today’s landscape presents several potential problems around ALPR, including issues of oversight and data retention. The data is interesting to look at, Maass said, and provides insight that will help legislators understand how this technology manifests. But the EFF hasn’t reached any definite conclusions about what the OPD’s data means.

The EFF blog post showcasing the data contains a Google map (shown above) of more than 63,000 geographical points showing where and when a license plate was scanned by the department. An EFF-created video gives an idea of the pace of data collection as officers driving vehicles equipped with the scanners traveled their daily routes through the city.

In an attempt to glean some kind of meaning from the data, EFF layered OPD’s ALPR data with other map layers like per capita income, crime data and mosque locations. The EFF discovered that lower-income neighborhoods saw a disproportionate amount of license plates being scanned by police, but poor neighborhoods also tend to have more crime, which explains greater police presence. EFF combined mosque locations with the data to see if police were using the technology to gather intelligence on Muslim populations, and while some mosques fell within areas that were frequently scanned, others did not, so proving any correlation from this data alone would be difficult. 

The data reveals a few other points of minor interest, but the main purpose of obtaining the data was simply to demonstrate that such data is of public interest, Maass said. The EFF is now engaged in a lawsuit with the Los Angeles Police Department (LAPD) because the LAPD refuses to share its ALPR data on the grounds that it's being used to pursue criminal investigations -- a claim that gets at the heart of the dispute between privacy activists and law enforcement.

The EFF’s main objection to ALPR technology, Maass said, is that it could be abused if data retention policies aren’t governed closely. “That concerns us," said Maass, "because they’re collecting so much data that could be used to paint detailed portraits of people’s comings and goings around the city."

Using the technology to specifically target known stolen vehicles or known criminals is less of a concern, he said, because in those cases the technology is being used in a focused and legitimate manner. But when police use technology as a means to create a broad dragnet that can gather and collect information about everyone, he added, it becomes a major privacy issue.

Privacy policies around ALPR vary by state and region, while many departments aren’t governed by a targeted privacy policy at all. “California has a restriction on the California Highway Patrol, but they don’t have one for local jurisdictions," Maass said, "so in that case, city by city, county by county, you’re going to have different policies."

As parking enforcement and police look for ways to expand their knowledge base and resources, they increasingly look to ALPR as a means to enforce the law. The public and legislators must get involved with the issue, Maass said, because police sometimes doesn’t think outside of their primary objective of law enforcement and into issues like privacy.

“If you were to close your eyes and throw a dart at a map,” he said, “chances are you would hit a jurisdiction that is considering LPR if they don’t already have it.”

The Oakland Police Department declined to comment on this story.

Colin wrote for Government Technology and Emergency Management from 2010 through most of 2016.