PhotoYou've known for years now about the ever-growing presence of license plate scanners that record and store the realtime movements of essentially all vehicles on public roadways where scanners are in use —either fixed-position scanners recording passersby on various roads, or roving scanners attached to police cars and other vehicles.

Perhaps you've even pondered the privacy implications of having all this information stored in a publicly accessible database, and wondered just how much personal information might be gleaned from these public records.

Cyrus Farivar from ArsTechnica wondered the same, and this week published the analysis of a public records request he'd filed with the city of Oakland, California, to see the results of the 33 automated license plate readers (LPRs) the police department operates throughout the city:

… we obtained the entire LPR dataset of the Oakland Police Department (OPD), including more than 4.6 million reads of over 1.1 million unique plates between December 23, 2010 and May 31, 2014. …

After analyzing this data with a custom-built visualization tool, Ars can definitively demonstrate the data's revelatory potential. Anyone in possession of enough data can often—but not always—make educated guesses about a target’s home or workplace, particularly when someone’s movements are consistent (as with a regular commute).

For instance, during a meeting with an Oakland city council member, Ars was able to accurately guess the block where the council member lives after less than a minute of research using his license plate data. ...

No detectives needed

Indeed, it doesn't require Sherlock Holmes to deduce that the address where a person's car is parked overnight every night just might be where that person lives, nor to figure out that the daytime address where the car goes every Monday through Friday might correspond to that person's place of employment.

But, for all the ways this might destroy the privacy of everyday innocent people, at least it could help catch a few criminals too, right?

A few criminals, yes. Very few:

LPR collection began in Oakland back in 2006, and an early OPD analysis showed that the overwhelming majority of the data collected was not a “hit.” In April 2008, the OPD reported to the city council that after using just four LPR units for 16 months, it had read 793,273 plates and had 2,012 hits—a “hit rate” of 0.2 percent. In other words, nearly all of the data collected by an LPR system concerns people not currently under suspicion.

Despite this, in that same report, then-OPD Deputy Chief Dave Kozicki (who has since retired) dubbed the LPR setup an “overwhelming success.” Today, OPD's LPR hit rate has fallen slightly, to just 0.16 percent.

The privacy-invading potential of license plate scanners has been an issue in California (among other states) for awhile now. Last May, California state senator Jerry Hill (D-San Mateo) conducted an experiment to demonstrate the invasive potential of the scanners: he hired a private detective to track his wife's whereabouts and habits. The detective never had to actually “track” her; he merely paid to acquire her license plate records to get a record of where and when she drove and parked her car — including a particular gym 100 miles from her home.

Other public-record surveillance data is even more intrusive. A man in San Leandro filed a public-records request and learned that, in addition to more than 100 photos of his license plate in various locations, the public record also includes photographs of his daughters standing in their own driveway.

No escape

Realistically, there's no getting rid of the license plate scanners and other cheap, ubiquitous recording devices already blanketing the public sphere — they will only grow more numerous as the technology continues improving.

But it is possible to put legal limits on how much of this data police and other agencies can collect, or how long they can keep it. Earlier this month, for example, the Virginia State Senate voted unanimously to pass a bill which, if signed into law, would limit police to storing license plate scanner records for only seven days, unless there is an active criminal investigation.

In California there is no state limit, though some municipalities set limits of their own: Menlo Park holds data for 30 days, Los Angeles for two years. Oakland currently has no legal limit in place.

The vast amount of data ArsTechnica got from Oakland comes from just 33 license plate readers in a city covering 78 square miles. In other cities, license plate scanners are even more common. As early as 2011, there were over 250 scanners in Washington D.C. (68.3 square miles) and its immediate suburbs.

Public record

Since license plate scanner data is usually public information, that means anybody can access it, without a warrant. 

ArsTechnica, as part of its experiment with the Oakland records, searched for the license plate information for Howard Matis, a physicist with the Lawrence Berkeley National Laboratory. Sure enough, Ars was able to determine where Matis lived and worked, as well as a couple of locations where he and his wife frequently visited.

“If anyone can get this information, that’s getting into Big Brother,” Matis said. “If I was trying to look at what my spouse is doing, [I could]. To me, that is something that is kind of scary. Why do they allow people to release this without a law enforcement reason? Searching it or accessing the information should require a warrant.”

One answer to that is that public information belongs to the people. It is, after all, gathered by public employees using publicly-owned equipment, all at taxpayer expense. Journalists have fought for centuries to keep governments from locking up information that rightfully belongs to taxpayers. Rather than reverting to more secrecy, press freedom advocates suggest the government simply stop collecting the information. Failing that, they can emulate Virginia and keep it for only a short time.

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