Automatic License Plate Readers allow governments and private corporations to keep track of the location and occupants of millions of vehicles simultaneously, with very little effort. The basic technology is nothing new: It was invented in 1976 and was already leading to arrests by 1981. However, as with many other types of technological advances, such as pattern analysis and facial recognition, these relatively old technologies are being implemented with increasing frequency and accuracy due to the drastic drop in data storage and processing costs. [Ed.: For more background, see Mike Silliman's summer post on the subject here.]

Recent investigatory work by the ACLU [PDF] highlighted the extent to which this technology is becoming commonplace, as well as its potential for abuse. Because it can be deployed easily and inexpensively, automatic license plate readers can almost function as pseudo-GPS trackers — for every car on the road. Moreover, retention policies for the collected data are uncertain. Against this backdrop, the ACLU turns to language from an opinion provided in United States v. Maynard, 615 F.3d 544 (D.C. Cir. 2010) to highlight the capacity for seemingly innocuous location data to reveal deeply personal facts:

“A person who knows all of another’s travels can deduce whether he is a weekly church goer, a heavy drinker, a regular at the gym, an unfaithful husband, an outpatient receiving medical treatment, an associate of particular individuals or political groups — and not just one such fact about a person, but all such facts.”

The ACLU investigation also highlights the extent to which law-abiding citizens’ data is collected, despite the purported focus on criminal activity. One jurisdiction, Maryland, voluntarily provided records to the ACLU. Maryland defines a ‘hit’ as being a plate (or a mistakenly read plate) that is associated with some criminal or administrative violation. Of 85 million license records collected in that state in 2012, 0.2 percent were hits while 99.8 percent were not. Almost all of the hits, or 97 percent, were administrative violations (e.g., an expired emissions test). But without reliable information on how much information is being collected and how long it is being stored, we can’t accurately weigh the costs and benefits of collection. While some states have made this information available, others have no clear policies in place. Further, it remains unclear whether and to what extent jurisdictions are sharing the information among themselves, with the federal government, or with private companies.

Most of the focus on the technology focuses on the question of whether the intrusions on personal liberty outweigh the law enforcement benefits provided by the technology. This, however, is a political question that, as long as the relevant information is public (ahem, NSA), can best be left to political processes. Of course, at some point there may be a constitutional question whether these readers constitute a fourth amendment search, but current legal thinking [PDF] seems to have reach consensus that it is does not reach that threshold. A more proximate legal question may be what follows after a positive hit on a vehicle. If a vehicle is flagged by the computer, what rights do the police then have to stop and investigate the vehicle and the driver, who may not even be responsible for the violations associated with that vehicle, even if such violations actually exist and are not the product of camera or computer error.

The majority of courts have held that hits from automatic license plate readers provide the articulable suspicion necessary to perform the traffic stop. This reason is based on previous holdings [PDF] that checking license plates against a registry also meets this standard, and that this process really just augments the sensory faculties of the officer. While this reasoning seems compelling, there is something missing. If the numbers provided by the jurisdictions that have disclosed them are accurate, then each day many more individuals should be getting pulled over and subjected to a reasonable suspicion-supported Terry stop. If police are only subjecting only some plate reader hits to stops, how are they deciding who that will be? Are the distinctions they are making allowed under the law? For instance, can license plate readers be used by police to pretextually stop vehicles of those who appear to be in this country illegally on the basis of their skin color or where they live?

As long as automatic license plate readers provide a legal justification to pull over and investigate many more people than the police are actually capable of investigating, the technology will be highly susceptible to abuse in a manner otherwise undetectable. Perhaps instead of asking an officer why they pulled over an individual on the basis of a license plate hit, they should be asked why they didn’t pull over 50 other cars that gave the same hit. That latter question seems to be much less articulable under Terry and much more likely to ensure that this technology is not used as an blanket justification to pursue individuals that were otherwise of interest for inarticulable reasons.

Matt Ginther

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