ALPR Technology, Privacy, and the Fourth Amendment

Introduction to ALPR Technology

The newest and fastest way for law enforcement to check the license plates on automobiles — using cutting-edge technology — is called the Automatic License Plate Recognition system (ALPR). Police departments are currently using this technology in many areas around the United States, and authorities believe this system can catch criminals and perhaps also identify terrorists who may be driving stolen vehicles. The system can gather thousands of plate numbers in an hour. Privacy groups and lawyers for the American Civil Liberties Union are raising important questions about this technology: does the collecting of license plate numbers — along with the names of car owners and the place, date, and time at which each plate was scanned — and storing them in a database constitute a fundamental violation of Fourth Amendment protections? These and other issues are reviewed in this paper.

ALPR in Practice: News Coverage and Deployment

An article in the Washington Examiner points out that several police departments in Virginia's Prince William County are now outfitted with technology that reads license plates as vehicles speed past patrol cars. The article reports that the county has recovered ten stolen vehicles through this technology, located seven stolen license plates, and "arrested four people in the six months" the technology has been in place (Sherfinski, 2008, p. 1). The camera is positioned on the patrol car, and the license plates on cars — regardless of how slowly or quickly the vehicle is traveling — are all scanned instantly. One notable point is that the Department of Homeland Security wished to receive a grant proposal to expand the use of ALPR throughout northern Virginia. The Homeland Security Department suggested that these license plate checks could help law enforcement capture "suspected terrorists" and those suspected of being involved in "terrorist-type crimes" (Sherfinski, p. 1).

In the Washington Post, Sheridan (2008) reports that "top homeland security officials from Maryland, Virginia and the District of Columbia … agreed to spend $4.5 million" on the installation of approximately 200 ALPR units for the Washington, D.C. area. The purpose of this expenditure was to "thwart potential terrorist attacks," not just to find "scofflaws and car thieves" (Sheridan, 2008, p. 1). When the ALPR picks up a license plate number, it is instantly run through a database and a "criminal watch list," according to Arlington Police Captain Kevin Reardon. If there is a "hit," the database reports back to the officer that the license plate belongs to a stolen car or that the owner is wanted for questioning.

"What's going to happen to the data?" asks Marc Rotenberg, executive director of the Electronic Privacy Information Center, an organization concerned with civil liberties matters. "The Department of Homeland Security will now have an enormous amount of information about the travel habits of Washington area residents" (Sheridan, p. 2).

Fourth Amendment Implications of License Plate Scanning

The constitutional amendment most applicable to this issue is the Fourth Amendment, which reads: "The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized" (U.S. Constitution).

There are privacy implications surrounding the use of ALPR, although the courts have not yet examined this particular issue in the context of the Fourth Amendment. The courts have, however, ruled on many related cases, and there are instructive links to the question of ALPR. David J. Warner, writing in the Loyola of Los Angeles Law Review, explains that the historical purpose of the Fourth Amendment was to prevent "the use of government force to search a man's house, his person, his papers," and it cannot be properly translated into a "general constitutional 'right to privacy'" (Warner, 2007, p. 859). Accordingly, the relevant inquiry is two-pronged: (a) was the action taken a "search," and (b) if so, was that search unreasonable? (p. 859).

Warner points to the early case Olmstead v. United States, in which the government wiretapped a defendant's phone conversation without trespassing on the defendant's property. The Supreme Court focused on the tort of trespass and ruled that, because there was no trespass, there was no "search" (Warner, p. 860). Subsequent decisions modified this approach. In United States v. Knotts, police hid a radio transmitter in a container of chloroform that the defendant had purchased, then tracked the transmitter to a cabin in Wisconsin. The Court ruled that the use of the transmitter "was constitutional and did not amount to a 'search'" (Warner, p. 861).

The Court's rationale in Knotts was that the transmitter "was not used to discover any information from inside the cabin or that was not visible to the naked eye," and therefore there was no unreasonable search (Warner, p. 861). A key question regarding ALPR technology is whether scanning license plates is analogous, given that the numbers on a plate lead police to personal information not otherwise immediately visible. In United States v. Karo, the Court ruled that placing a radio transmitter in a five-gallon drum to track an alleged drug dealer — a warrantless action — was an "unreasonable" search because an electronic device was used to reveal information "otherwise not obtainable from outside the home" (Warner, pp. 861–62). Whether ALPR data collection falls closer to Knotts or Karo remains an open legal question.