License Plate Readers

Law enforcement use of automated license plate readers has become very widespread. It raises several interesting legal and practical issues which I briefly explore below.

What are they? License plate readers are electronic devices – basically, enhanced cameras – that scan each passing car, detect the license plate, read it, and record it. The devices may also photograph the plate, such as when the plate matches a “hot list” of stolen plates. The readers may be stationary, mounted on a light pole or an overpass, or they may be mobile, mounted on a police vehicle. When mounted on a vehicle, they may send an alert to the officer driving a vehicle when they detect a noteworthy plate.

Widespread use. According to public records obtained by the ACLU, at least the following North Carolina law enforcement agencies are using license plate readers:

  • Charlotte-Mecklenburg Police Department
  • High Point Police Department
  • Jacksonville Police Department
  • Raleigh Police Department
  • Washington Police Department
  • Wilmington Police Department
  • Wilson County Sheriff’s Office
  • Wrightsville Beach Police Department

Other agencies such as the Fayetteville Police Department and the Greenville Police Department, have experimented with or are exploring the use of plate readers.

I don’t know how the ACLU identified agencies to query, or how it decided which responses to post online, but a substantial majority of the agencies whose responses it posted acknowledged using plate readers. Survey data suggests that a majority of all law enforcement agencies already use the readers, and I assume that even more agencies will do so in the future as the technology becomes better known and less expensive. In a few years, every police vehicle may be topped with a plate reader.

Plate readers and traffic stops. Plate readers aren’t perfect, as illustrated by Green v. City and County of San Francisco, 2011 4434801 (N.D. Cal. Sept. 23, 2011) (unpublished), a civil suit arising out of a plate reader’s mistaken determination that plate 5SOW-3-50 matched stolen plate 5SOW-7-50, and the resultant “high risk felony stop” at gunpoint of an innocent motorist. In light of the devices’ fallibility, when an officer receives an alert from a plate reader mounted on her police vehicle, may she rely on the alert to stop the vehicle identified by the reader?

At least in many circumstances, the answer may be yes. See Hernandez-Lopez v. State, 319 Ga. App. 254 (Ga. Ct. App. 2013) (reasonable suspicion supported a vehicle stop where a plate reader gave an officer a “‘wanted person’ alert” after detecting a license plate associated with a person who had previously failed to appear in court; the officer noted that the wanted person was a male as was the driver of the vehicle); People v. Davila, 901 N.Y.S.2d 787 (N.Y. Sup. Ct. 2010) (a plate reader alerted to a vehicle with suspended registration; this provided reasonable suspicion to support a traffic stop). But cf. Rodriguez v. State, __ S.E.2d __, 2013 WL 1767660 (Ga. Ct. App. 2013) (a driver was issued traffic citations and failed to appear in court to answer them, so an arrest warrant was issued for the driver; later, a cruiser-mounted license plate reader spotted the license plate associated with the previous citations; officers stopped the vehicle based on the match; although the person driving at that point was not the subject of the arrest warrant, officers searched the car based on consent and found marijuana; a majority of the appellate court found that the defendant waived her right to contest the validity of the stop, while a dissenting judge would have ruled that, absent evidence that the vehicle was registered to the fugitive [information that the plate reader system did not supply] or that the driver shared physical characteristics with the fugitive [which she did not, as the fugitive was a male] there was not a sufficient basis for the stop).

Privacy concerns. The ACLU just released a report on readers, entitled You Are Being Tracked. The report acknowledges the crime-solving potential of the devices, but argues that the proliferation of the readers and the long retention of the data that they collect poses a privacy threat:

The implementation of automatic license plate readers poses serious privacy and other civil liberties threats. More and more cameras, longer retention periods, and widespread sharing allow law enforcement agents to assemble the individual puzzle pieces of where we have been over time into a single, high-resolution image of our lives. The knowledge that one is subject to constant monitoring can chill the exercise of our cherished rights to free speech and association. Databases of license plate reader information create opportunities for institutional abuse, such as using them to identify protest attendees merely because these individuals have exercised their First Amendment-protected right to free speech. If not properly secured, license plate reader databases open the door to abusive tracking, enabling anyone with access to pry into the lives of his boss, his ex-wife, or his romantic, political, or workplace rivals.

Law enforcement generally disagrees, noting the absence of actual examples of abuse, in contrast to the plentiful real examples of plate readers solving crimes like vehicle theft (N&O story) and murder (Jalopnik story). One of the key issues in this area is how long the license plate data should be retained. Agencies vary in this regard, with retention periods ranging from 48 hours to indefinitely.

Fourth Amendment issues. Whether the use of plate readers is a privacy problem or not, at least under conventional Fourth Amendment doctrine, using a plate reader isn’t a “search” because the reader is just looking at something in public view. See United States v. Wilcox, 2011 WL 679416 (11th Cir. Feb. 28, 2011) (unpublished) (defendant argued that “the use of the tag reader technology amounted to unconstitutional surveillance that violated his reasonable expectation of privacy,” but the court disagreed, finding no expectation of privacy in the defendant’s license plate as it was plainly visible on the public roads). Cf. State v. Chambers, 2010 WL 1287068 (N.C. Ct. App. April 6, 2010) (unpublished) (“Defendant’s license tag was displayed, as required by North Carolina law, on the back of his vehicle for all of society to view. Therefore, defendant did not have a subjective or objective reasonable expectation of privacy in his license tag. As such, the officer’s actions did not constitute a search under the Fourth Amendment.”).

However, when data gathered from multiple plate readers is combined, and is retained over time, one could argue that the resulting database approaches continuous surveillance, akin to constant tracking of every vehicle. This may eventually implicate the so-called mosaic theory of the Fourth Amendment. The Supreme Court’s decision in United States v. Jones, __ U.S. __, 132 S.Ct. 945 (2012), the GPS tracking case I discussed here, suggests a receptiveness to that idea. That is, a majority of the Court appears sympathetic to the notion that long-term monitoring of individuals’ movements without a search warrant may be forbidden by the Fourth Amendment. Plate readers likely are not yet ubiquitous enough to raise a serious Fourth Amendment question about their use, but as their presence grows, that day may come.