License Plate Readers - What You Didn't Know

Law Enforcement and Technology: Use of Automated License Plate Readers

Over the past couple of decades, law enforcement use of automated license plate readers (ALPRs; also referred to as LPRs) has increased. These tools are now relatively commonplace in policing. 

According to the Bureau of Justice Statistics’ 2020 Law Enforcement Management and Administrative Statistics Survey, larger law enforcement offices were more likely to use ALPR technology than smaller offices; nearly 90% of sheriffs’ offices with 500 or more sworn deputies reported using the technology, and of police departments serving over 1 million residents, 100% used ALPRs. 

ALPRs are camera systems that capture the license plate data of passing vehicles, along with related information. They are generally available in fixed and mobile formats. Fixed ALPR systems are mounted in specific locations, often using existing infrastructure such as light poles, traffic lights, buildings, or bridges. Mobile ALPR systems are frequently mounted on police vehicles or privately contracted vehicles. ALPRs automatically capture images or videos of passing vehicles. An algorithm then detects the license plates within the photo/video and reads the numbers. (ALPR technology can also detect additional, related information, including vehicle type and color, global positioning system [GPS] location data, and date and time.) 

After they capture and catalog license plate information, ALPR systems can compare these data against various databases, including what are known as hot lists, which contain license plates linked to vehicles of interest. If there is a match to a hot list license plate, the ALPR system can alert a police officer in real time. 

Law enforcement agencies may use ALPRs for a variety of proactive and reactive policing purposes, including gathering intelligence and evidence, helping identify potential suspects, and facilitating crime scene analysis. 

There does not appear to be publicly available data on the frequency and extent to which ALPR technology is used for various purpose areas, and there are no data on its use at various phases of the criminal justice system—from generating investigative leads and helping establish probable cause for an arrest or indictment to serving as evidence in courtrooms.

Source: Congressional Research Service