The Evolution of Law Enforcement: Understanding New Police Car License Plate Scanners

Automated License Plate Readers (ALPRs) have become an increasingly prevalent technology in modern policing. These sophisticated, computer-controlled camera systems are designed for rapid data capture and analysis. Typically found mounted on street infrastructure, mobile trailers, or directly on police vehicles, ALPRs automatically record license plate numbers, along with crucial contextual data such as location, date, and time. This information, often including vehicle and occupant images, is then transmitted to central servers for processing and storage.

According to vendors like Vigilant Solutions, this extensive data collection offers law enforcement agencies powerful tools. By accessing historical ALPR data, police can trace vehicle movements to ascertain presence at crime scenes, identify travel patterns, and even link vehicles of interest. Furthermore, agencies often engage in data sharing, expanding the reach and scope of this surveillance network across jurisdictions.

However, the aggregation of ALPR data raises significant privacy concerns. The detailed records can create a comprehensive profile of a driver’s life, potentially chilling activities protected by the First Amendment. The technology’s capacity to track visits to sensitive locations such as healthcare facilities, religious centers, or political gatherings highlights its potential for intrusive surveillance.

While license plates are a mandatory public display for vehicle operation, the automated and indiscriminate collection of this data by ALPRs is a contentious issue. Millions of ordinary citizens, the vast majority unconnected to any criminal activity, are subjected to continuous tracking. This article delves into the workings of these systems, their applications, and the growing debate surrounding their use.

Decoding ALPR Systems: Stationary, Mobile, and Trailer-Based Technologies

Automated license plate readers can be categorized into three primary types, each designed for specific operational scenarios:

Stationary ALPR Cameras: Fixed Surveillance Points

Stationary ALPR systems mounted on traffic infrastructure for continuous monitoring.

Stationary, or fixed ALPR cameras, are permanently installed at strategic locations. These include traffic lights, utility poles, facility entrances, and freeway ramps. These cameras are designed to capture license plates of vehicles passing within their field of view.

The strategic deployment of multiple stationary ALPR cameras along roadways enables law enforcement to monitor vehicle direction and speed. A network of these cameras allows for real-time vehicle tracking. Furthermore, the long-term storage of collected data enables authorities to retrospectively analyze vehicle movements, potentially inferring residential or workplace locations based on frequently recorded plate sightings. Notably, some smaller municipalities utilize ALPRs at town entrances and exits, effectively creating a digital perimeter, logging every vehicle entering or leaving the area. In some instances, ALPR cameras are discreetly integrated into everyday objects like traffic cones or even disguised as cacti to minimize public awareness.

Stationary ALPR systems are frequently integrated with other traffic management and enforcement technologies, such as red-light and speed enforcement systems, and automated toll collection on highways and bridges.

Mobile ALPR Cameras: On-the-Move Data Collection

Mobile ALPR technology integrated into a police patrol vehicle for dynamic data capture.

Mobile ALPR systems are typically mounted on police patrol vehicles, transforming them into roving data collection units. Activated at the start of police shifts, these systems continuously operate, capturing license plate data as officers patrol their designated areas.

Mobile ALPRs are particularly effective at scanning parked vehicles. Driving through parking lots, a patrol car equipped with mobile ALPR can rapidly collect data from hundreds of vehicles in a short period.

Law enforcement also employs mobile ALPRs for a practice known as “gridding.” This involves systematically driving through every street in a neighborhood to collect license plate data on all residents, raising concerns about blanket surveillance.

Private companies, such as Vigilant Solutions, also utilize mobile ALPRs to gather license plate data, which they then commercialize by selling it to law enforcement agencies and other interested parties, expanding the reach of vehicle tracking beyond public sector operations.

ALPR Trailers: Deployable Surveillance Units

ALPR technology deployed on a mobile trailer for temporary or strategic surveillance operations.

ALPR technology is also available in trailer-mounted configurations. These mobile units can be towed and deployed to specific locations for extended periods. Functioning similarly to fixed ALPRs, trailers offer flexibility without requiring permanent infrastructure installation. The Drug Enforcement Administration (DEA) has historically utilized ALPR trailers, often disguised as speed enforcement units, to monitor vehicle movements in areas along the U.S.-Mexico border. Police have also strategically positioned ALPR trailers or ALPR-equipped vehicles near events such as gun shows and political rallies, raising concerns about monitoring attendees and their activities.

ALPR Databases: Centralized Data Repositories

The vast amounts of data collected by ALPR systems are generally stored in databases for extended periods, commonly up to five years and sometimes indefinitely. These databases may be managed by individual police departments or outsourced to private companies like Vigilant Solutions or Flock Safety. Agencies without their own ALPR infrastructure can access data collected by others through regional sharing networks operated by these private vendors. Furthermore, independent commercial ALPR databases exist, where companies contract with individuals to equip private vehicles with ALPR cameras. The collected data is then sold to various industries, such as insurance companies, but law enforcement can also subscribe to these commercial data feeds, further broadening data access.

Hotlists: Targeted Vehicle Identification

Law enforcement agencies frequently utilize “hotlists,” pre-loaded lists of license plates that trigger alerts within the ALPR system. These lists commonly include plates of stolen vehicles or vehicles associated with outstanding warrants. Officers can also create custom hotlists for specific investigations. When an ALPR system detects a plate on a hotlist, it immediately alerts officers in patrol vehicles (for mobile ALPRs) or the relevant agency (for fixed ALPRs). Some hotlists encompass vehicles linked to minor offenses, including misdemeanors and traffic violations. In some instances, agencies use hotlists to proactively identify and stop vehicles associated with unpaid citations for revenue generation purposes.

The Breadth of ALPR Data Collection: Beyond License Plates

ALPR systems capture a comprehensive dataset extending beyond just license plate numbers. They record precise location data alongside the exact date and time of each plate capture. Advanced systems can also identify the vehicle’s make and model. These systems are capable of processing thousands of license plates per minute, generating massive datasets. One vendor boasts a dataset exceeding 6.5 billion scans, growing by 120 million data points monthly, illustrating the sheer scale of data accumulation.

By cross-referencing ALPR data points, it’s possible to triangulate vehicle movements, determining direction and speed of travel. Aggregated over time, this data reveals detailed historical travel patterns. Algorithms can analyze this data to identify regular routes and even predict future vehicle locations. ALPR data also reveals all vehicles present at a particular location over time, offering insights into patterns of congregation.

While ALPR data typically doesn’t include driver names directly, law enforcement can utilize other databases to link license plate numbers to registered owners.

Furthermore, the images captured by ALPRs can contain visual information beyond license plates. These images can include pictures of the vehicle itself, occupants (drivers and passengers), the immediate surroundings, and even individuals entering or exiting vehicles. Some systems create “vehicle fingerprints,” incorporating details such as vehicle color, make, model, physical damage, and bumper stickers, adding layers of detail to the collected data.

Law Enforcement Applications of ALPR Technology: Real-Time and Historical Investigations

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Visualization of ALPR data collection patterns by Oakland Police Department vehicles.

ALPR technology enables indiscriminate data collection, capturing information on vast numbers of individuals, the majority of whom are not suspected of any wrongdoing. By mapping vehicle locations and times and tracing past movements, law enforcement can construct detailed profiles of drivers’ lives, identifying behavioral patterns and potentially predicting future actions. This capability exists despite the fact that only a minuscule fraction of collected data is ever directly relevant to active public safety concerns. Unlike traditional manual license plate collection, which is limited and requires officers to make discretionary choices about which vehicles to track, ALPR technology removes these constraints, enabling mass surveillance with significantly reduced manpower.

A 2021 EFF report analyzing data from 63 California law enforcement agencies found that only 0.05% of ALPR data collected was pertinent to a public safety interest at the point of capture.

Law enforcement agencies primarily utilize ALPR technology for two broad purposes:

Real-Time Investigations: Immediate Vehicle Identification and Tracking

By adding specific license plates to a “hotlist,” law enforcement can leverage ALPRs to automatically identify and track these vehicles in real-time. Plates are commonly added to hotlists for vehicles reported stolen or linked to outstanding warrants. Investigative hotlists may also include vehicles observed at crime scenes, associated with criminal suspects, or believed to be connected to gang activity. Notably, hotlists often extend to vehicles associated with less serious offenses as well.

Historical Investigations: Retrospective Data Analysis

Given that ALPR systems collect data on nearly all vehicles, not just those on hotlists, law enforcement can search and analyze historical data using plate numbers, partial plates, or physical addresses. For instance, in the case of a convenience store robbery, investigators can query the ALPR database for all vehicles recorded near the location at the time of the incident. They can then further investigate those plate numbers to identify other locations where the same vehicles have been recorded, potentially uncovering patterns or connections.

It’s important to note that while hotlist alerts can prompt police action, law enforcement training and policies often mandate visual confirmation of a plate match before initiating a stop. Errors in machine reading, coupled with a failure to manually verify plate numbers, have resulted in wrongful stops and detentions.

While law enforcement agencies cite successes such as recovering stolen vehicles and locating abducted children using ALPR data, the technology is also deployed for mass enforcement of minor offenses, including tracking uninsured vehicles or individuals with overdue court fees, raising concerns about mission creep and disproportionate impact.

Data retention policies for ALPR data vary significantly across agencies, ranging from short periods of days to several years. Private companies, however, may retain data indefinitely, further complicating the landscape of data privacy and control.

Key Players in the ALPR Technology Market

Vigilant Solutions (a subsidiary of Motorola Solutions) and Flock Safety are prominent vendors in the ALPR technology market within the United States. Other notable companies include Rekor, Elsag, Axon, Perceptics, and Jenoptik.

Vigilant Solutions, through its sister company Digital Recognition Network, aggregates ALPR data collected privately through partnerships with vehicle repossession companies. Flock Safety similarly partners with homeowners associations, gaining access to community-level ALPR data that is then offered to law enforcement. Both Vigilant Solutions and Flock Safety facilitate data sharing among law enforcement agencies nationwide, creating expansive interconnected surveillance networks.

The Privacy and Civil Liberties Threats of ALPRs

ALPR technology, while presented as a law enforcement tool, poses significant threats to individual privacy and community rights.

Instances of abuse and misuse by law enforcement agencies have been documented. The NYPD, for example, targeted a Muslim community by recording license plates of vehicles parked near a mosque. In Birmingham, UK, police similarly focused surveillance on Muslim communities under false pretenses. EFF data analysis of Oakland Police Department ALPR usage revealed disproportionate deployment of ALPR-equipped vehicles in low-income communities and communities of color, raising concerns about discriminatory surveillance practices.

Furthermore, internal misuse of law enforcement databases, including ALPR data, by individual officers is a recurring problem. A Washington, D.C. police officer was convicted of extortion after using license plate lookups to identify and blackmail individuals visiting a gay bar. More recently, a Kansas police officer was arrested for allegedly using a Flock Safety ALPR database to stalk his estranged wife, highlighting the potential for personal abuse of these powerful tools.

Beyond intentional misuse, ALPR system errors can lead to severe consequences. Misread plates have resulted in wrongful stops and detentions. The case of Denise Green in San Francisco, who was wrongly pulled over and handcuffed at gunpoint due to an ALPR error, led to a Ninth Circuit Court of Appeals ruling that technology alone cannot justify such stops. However, this ruling is not universally binding, leaving individuals vulnerable to similar errors and overreactions by law enforcement. A more recent incident in Aurora, Colorado, saw a group of Black youths traumatized after their vehicle was mistakenly flagged as stolen by an ALPR system.

The long-term storage of aggregated ALPR data exacerbates privacy risks, making the data more vulnerable to misuse and data breaches. Even well-resourced agencies like Customs & Border Protection have experienced data breaches at ALPR vendors, such as the Perceptics hack that resulted in traveler data being leaked online. Reasonable data retention limits, clear access policies, and robust audit processes are crucial to mitigate these risks. Ideally, a privacy-centric approach would involve deleting ALPR data immediately if a vehicle does not match a hotlist, minimizing the collection of data on law-abiding citizens.

ALPR technology also presents a heightened risk to vulnerable communities, including immigrant populations and individuals seeking reproductive healthcare services. The technology can be used to track individuals visiting immigration centers or healthcare clinics, potentially chilling access to essential services.

EFF’s Advocacy for ALPR Accountability and Transparency

The Electronic Frontier Foundation (EFF) has been actively engaged in addressing the privacy threats posed by ALPR technology since 2012 through public records requests, litigation, and legislative advocacy.

ALPR Litigation: Challenging Data Access and Sharing

EFF and the ACLU of Southern California jointly sued the Los Angeles County Sheriff’s Department and the Los Angeles Police Department after these agencies refused to disclose ALPR data, claiming it was exempt from the California Public Records Act as investigative records. This argument was challenged as effectively placing all residents under suspicion, a point echoed even by an LAPD lawyer and a California Supreme Court Justice during legal arguments. In 2017, the California Supreme Court ruled in favor of EFF and ACLU, compelling the agencies to release the data.

In 2021, EFF and the ACLU further litigated against the Marin County Sheriff’s Office in Lagleva v. Marin County Sheriff, challenging the sheriff’s practice of sharing ALPR data with out-of-state agencies, including Immigration & Customs Enforcement (ICE), in violation of California law. A settlement was reached where the sheriff agreed to cease data sharing outside of California.

EFF has also filed amicus briefs in cases outside California, including a case in Virginia concerning excessive ALPR data storage and cases in Massachusetts and Nevada challenging law enforcement searches based on ALPR data.

ALPR Accountability and Transparency Initiatives

In 2015, California enacted S.B. 34, legislation requiring ALPR users to implement data protection measures, maintain access logs, hold public meetings before initiating ALPR programs, establish usage and privacy policies, and restrict data sharing to other public agencies.

EFF has coordinated volunteer efforts to collect and analyze ALPR policies across California, publicly highlighting agencies failing to comply with S.B. 34. EFF has also independently filed public records requests with numerous agencies to shed light on ALPR data usage through its Data Driven and Data Driven 2 projects.

In 2019, EFF successfully advocated for a California State Audit of law enforcement agencies’ compliance with S.B. 34. The subsequent audit report substantiated EFF’s concerns, revealing widespread non-compliance, inadequate policies, and overly broad data sharing practices.