License Plate Scanner Car: Understanding ALPR Technology and Its Implications

Automated License Plate Readers (ALPRs) represent a significant advancement in surveillance technology. These sophisticated, computer-controlled camera systems are designed for rapid data capture and analysis. Typically seen mounted on street poles, traffic lights, highway overpasses, mobile trailers, or directly on police squad cars, ALPRs are constantly at work, automatically recording license plate numbers that come within their field of view. Alongside the plate number, ALPR systems capture crucial contextual data including the precise location, date, and time of each scan. The collected information often extends beyond just the license plate, frequently including photographs of the vehicle itself and sometimes even images of the driver and passengers. This wealth of data is then instantly uploaded to a central server, creating a vast and ever-growing database of vehicle movements.

Vendors highlight the benefits of this technology, asserting that the aggregated information empowers law enforcement to retrospectively analyze vehicle locations. This capability allows police to determine if a specific vehicle was present at a crime scene, identify travel patterns, and even uncover connections between different vehicles. Law enforcement agencies also have the option to share their data with a wide network of other agencies, amplifying the reach and scope of this surveillance network.

However, the extensive collection of ALPR data raises significant privacy concerns. When aggregated, this data can construct a detailed and intimate portrait of a driver’s life, potentially chilling activities protected by the First Amendment. The technology can be employed to monitor individuals who visit sensitive locations such as healthcare facilities, immigration support centers, gun stores, union offices, protest sites, or places of worship.

Drivers are obligated to display license plates on their vehicles by law, leaving them with no choice in whether their movements are tracked. This mandatory display makes the widespread use of automatic license plate readers particularly concerning, as it means the movements of millions of ordinary citizens are continuously tracked and recorded, even though the vast majority are not suspected of any criminal activity.

How License Plate Scanner Car Systems Operate

License Plate Scanner Car systems, or ALPRs, can be categorized into three main types, each suited for different applications and surveillance strategies.

Stationary or Fixed ALPR Cameras

Stationary automated license plate readers affixed to a traffic signal, demonstrating a common fixed installation for monitoring traffic.

Stationary ALPR cameras are designed for permanent installation at specific locations. These fixed points can include traffic signals, utility poles, building entrances, or freeway off-ramps. Typically, these cameras are configured to capture license plates only from vehicles that are moving and passing within their field of view.

Deploying multiple stationary ALPR cameras along a single road enables a more detailed level of vehicle tracking. By analyzing data from consecutive cameras, it’s possible to determine the direction a vehicle is traveling and its speed. With a sufficiently dense network of these cameras, law enforcement can achieve real-time tracking of vehicles. Furthermore, storing the collected data over time allows authorities to access historical travel patterns, revealing how often a particular license plate has been recorded at a specific location. This historical data can be used to infer where a driver likely lives or works. In smaller towns and municipalities, the strategic placement of ALPR cameras at town entrances and exits effectively creates a virtual gated community, where every vehicle entering or leaving is documented. To minimize public awareness and potential resistance, police sometimes disguise ALPRs as ordinary objects, such as traffic cones or even cacti.

Beyond license plate recognition, stationary ALPR cameras are frequently integrated with other traffic management and enforcement systems. They are commonly used in conjunction with automated red-light and speed enforcement systems and play a role in electronic toll collection on highways and bridges.

Mobile ALPR Cameras

Mobile automated license plate reader mounted on a police patrol car, illustrating how law enforcement utilizes vehicle-mounted scanners for on-the-move data collection.

Mobile ALPR systems are designed for dynamic data collection and are typically mounted on police patrol cars. These mobile units enable law enforcement officers to capture license plate data as they patrol city streets throughout their shifts. In most operational protocols, these systems are activated at the beginning of a shift and remain continuously running until the end, ensuring constant surveillance during patrol hours.

Mobile ALPR cameras are not only effective at scanning plates of moving vehicles but are also highly efficient at capturing data from parked cars. For instance, a patrol car equipped with a mobile ALPR can drive through a public parking lot and record hundreds of license plates within just a few minutes.

Police utilize mobile ALPRs for a tactic known as “gridding.” This method involves systematically driving an ALPR-equipped vehicle along every block of a neighborhood to gather intelligence on residents and their vehicles.

Furthermore, private companies like Vigilant Solutions also deploy mobile ALPRs to collect license plate data on a large scale. This privately gathered data is then sold to law enforcement agencies and other interested parties, creating a commercial market for vehicle location information.

ALPR Trailers

A speed enforcement trailer from the Walnut Creek Police Department, equipped with an automated license plate reader, showcasing a mobile and temporary surveillance solution.

ALPR technology is also available in the form of towable trailers. These ALPR trailers offer law enforcement a flexible surveillance solution, allowing them to deploy and relocate license plate readers to specific areas as needed. Trailers can be positioned in targeted locations for extended periods, collecting data in a manner similar to fixed ALPR systems but without requiring permanent installation. The Drug Enforcement Administration (DEA) has historically utilized these systems, sometimes disguised as speed enforcement trailers, to monitor vehicle movements in areas along the U.S.-Mexico border. ALPR trailers, and vehicles equipped with ALPRs, have also been strategically parked by police near gun shows and political rallies, indicating their use in monitoring specific events and gatherings. rallies.

ALPR Databases

The majority of data collected by ALPR systems is stored in databases for extended durations, frequently for up to five years. These databases may be managed directly by police departments, but often, their maintenance is outsourced to private companies such as Vigilant Solutions or Flock Safety. Law enforcement agencies that do not operate their own ALPR systems can gain access to data collected by other agencies through regional data-sharing systems and networks facilitated by these private companies. Furthermore, several companies operate independent, non-law enforcement ALPR databases. These entities contract with individuals to install cameras on private vehicles to collect license plate information. The data is then sold to various commercial entities, like insurance companies, but law enforcement agencies can also purchase subscription-based access to this commercial data.

Hotlists

Law enforcement agencies commonly utilize “hotlists,” which are pre-loaded lists of license plates that the ALPR system is specifically instructed to look for. These lists typically include plates associated with stolen vehicles or vehicles linked to outstanding warrants. Police officers also have the capability to create their own hotlists for specific investigative needs. When an ALPR camera scans a license plate that matches an entry on a hotlist, the system immediately sends an alert. This alert is directed to the officer in the patrol car if it’s a mobile ALPR or to the relevant agency in the case of a fixed reader. Some hotlists include plates linked to even minor misdemeanors and traffic violations. Certain agencies utilize these hotlists as a revenue-generating tool, targeting individuals with unpaid citations.

Types of Data Collected by a License Plate Scanner Car

License plate scanner cars, equipped with ALPR technology, capture a range of data points beyond just the license plate number. The core data collected includes the license plate number itself, along with precise location data and the exact date and time the plate was recorded. Advanced systems can also identify the make and model of the vehicle. These systems are incredibly efficient, capable of capturing thousands of plates per minute. One major vendor boasts a dataset exceeding 6.5 billion scans, growing at an astonishing rate of 120 million data points each month.

By combining data from multiple ALPR scans, it’s possible to determine the direction and speed of a vehicle through triangulation. Aggregating data over time creates a comprehensive history of a vehicle’s movements. Sophisticated algorithms can be applied to this data to identify regular travel patterns and even predict future locations. ALPR data also reveals all vehicles that have visited a particular location.

While the data typically does not include the driver’s name directly, law enforcement officers can utilize other databases to link individual names to license plate numbers, effectively bridging this gap.

In addition to license plate data, the photographs captured by ALPR systems can reveal images of the vehicle, drivers and passengers, and the immediate surroundings. Some systems can even capture images of people getting in and out of a vehicle. Certain advanced products create “vehicle fingerprints,” incorporating details such as the vehicle’s color, make, model, physical damage, and even bumper stickers for more granular identification.

How Law Enforcement Utilizes ALPR Technology

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Time-lapse visualization of data collected by Oakland Police Department vehicles equipped with license plate readers, demonstrating the scale of data accumulation.

ALPR data collection is indiscriminate, gathering information on millions of ordinary individuals. By mapping vehicle times and locations and tracing past movements, police can construct detailed profiles of drivers’ lives, identifying past behavior patterns and potentially predicting future actions. This occurs despite the fact that the vast majority of people whose license plate data is collected are not suspected of any crime. Prior to ALPR technology, law enforcement officers had to manually record license plates, a process that imposed practical limits on data collection and required officers to selectively choose which vehicles to track. ALPR technology removes these limitations, enabling the tracking of everyone and facilitating faster, broader data collection with significantly reduced staffing needs.

A 2021 report by the EFF analyzing data from 63 California law enforcement agencies revealed that only 0.05% of the data collected by ALPRs was relevant to a public safety interest at the time of capture.

Law enforcement primarily employs license plate readers for two general purposes:

Real-time Investigations

By adding a license plate to a “hot list,” officers can leverage ALPR systems to automatically identify or track specific vehicles in real time. License plates are commonly added to hotlists because the vehicle is stolen or associated with an outstanding warrant. Officers may also add a plate number if the vehicle has been observed at a crime scene, the owner is a suspect in an investigation, or the vehicle is believed to be linked to gang activity. Hotlists can also include vehicles associated with low-level offenses.

Historical Investigations

Since ALPRs typically collect data on all vehicles, not just those on hotlists, officers can search and analyze historical data using a plate number, partial plate, or physical address. For example, to investigate a convenience store robbery, an officer might input the store’s location into the ALPR system to identify vehicles that were present nearby at the time of the incident. The officer can then trace those plate numbers to uncover other locations where those vehicles have been recorded.

Training protocols, departmental policies, and legal guidelines in some jurisdictions advise officers that a hotlist alert alone may not be sufficient grounds for a vehicle stop. Officers are typically instructed to visually confirm the plate number to ensure accuracy. Failures to manually verify plate matches, combined with occasional machine errors, have resulted in wrongful stops.

Law enforcement agencies often claim that ALPR data has been instrumental in recovering stolen vehicles and locating abducted children. However, ALPR data has also been used for broad enforcement of less serious offenses, such as identifying uninsured vehicles or tracking individuals with overdue court fees.

The data retention period for ALPR data varies significantly across agencies, ranging from just a few days to several years. Some entities, including private companies, may retain the data indefinitely.

ALPR Technology Vendors

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

Vigilant Solutions, through its affiliated company Digital Recognition Network, offers access to a vast dataset collected privately through partnerships with repossession companies. These companies passively collect ALPR data using their own vehicles. Flock Safety has established similar partnerships with numerous homeowners associations, which provide data to law enforcement. Both Vigilant Solutions and Flock Safety facilitate data sharing among law enforcement agencies across the country, expanding the reach of ALPR surveillance networks.

Threats Posed by ALPR Technology

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

Instances of abuse by law enforcement agencies have been documented. For example, in New York, police officers drove through a street and electronically recorded the license plates of every vehicle parked near a mosque. In Birmingham, police targeted a Muslim community while misrepresenting the nature of the surveillance project to the public. Data obtained by the EFF from the Oakland Police Department revealed that ALPR-equipped vehicles were disproportionately deployed in low-income neighborhoods and communities of color, raising concerns about biased surveillance practices.

Furthermore, misuse of law enforcement databases, including license plate information, by individual officers is a recurring problem. In 1998, a Washington, D.C. police officer “pleaded guilty to extortion after looking up the plates of vehicles near a gay bar and blackmailing the vehicle owners.” More recently, an officer in Kechi, Kansas was arrested for allegedly accessing a Flock Safety ALPR database to stalk his estranged wife, highlighting the potential for personal misuse of this technology.

Beyond intentional misuse, ALPR systems are prone to errors in plate reading, which can lead to serious and unjust consequences. In 2009, a San Francisco woman, Denise Green, an African-American city worker, was pulled over at gunpoint, handcuffed, forced to her knees, and both she and her vehicle were searched. This traumatic event occurred because her car was incorrectly identified as stolen due to an ALPR error. Her case led the U.S. Ninth Circuit Court of Appeals to rule that technology alone cannot justify such a stop, but this ruling does not apply universally, leaving individuals vulnerable to similar errors. More recently, in Aurora, Colorado, a group of Black youths were traumatized by police after an ALPR system falsely identified their vehicle as stolen.

The accumulation of ALPR data over extended periods, or indefinitely, intensifies privacy risks and increases vulnerability to misuse and data breaches. Even U.S. Customs & Border Protection, a highly resourced law enforcement agency, experienced a data breach when its ALPR vendor, Perceptics, was hacked and sensitive data was published online. Implementing sensible data retention limits, establishing clear policies regarding data access within agencies, and robust audit and control processes are crucial steps to mitigate these risks. One of the most effective privacy safeguards would be for police to automatically delete data for any vehicle that does not match a hotlist.

Automated license plate readers can also be used to target immigrant communities and individuals seeking or providing reproductive health services, further expanding the scope of potential misuse and raising ethical concerns.

EFF’s Work on ALPR Technology

The Electronic Frontier Foundation (EFF) has been actively engaged in investigating and challenging the privacy threats posed by ALPR technology since 2012. EFF’s efforts include public records requests, litigation, and legislative advocacy.

ALPR Litigation

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 release ALPR data in response to public records requests. The agencies argued that the data was exempt under the California Public Records Act because it constituted investigative records. This argument implied that all residents of Los Angeles were under constant investigation, a notion that a lawyer for the LAPD and a California Supreme Court Justice both conceded sounded “Orwellian” during legal arguments. In 2017, the California Supreme Court ruled in favor of EFF and the ACLU, directing the case back to the Superior Court.

EFF and the ACLU also filed a lawsuit against the Marin County Sheriff’s Office in 2021, Lagleva v. Marin County Sheriff, on behalf of local activists. The lawsuit challenged the sheriff’s practice of sharing ALPR data with out-of-state agencies, including Immigration & Customs Enforcement (ICE), which violated California laws regulating ALPR use and prohibiting the sharing of criminal justice data for immigration enforcement purposes. As part of a settlement, the sheriff agreed to stop sharing data outside of California.

Beyond California, EFF has submitted amicus briefs in a Virginia lawsuit concerning the excessive storage of ALPR data, and in cases in Massachusetts and Nevada challenging law enforcement searches based on license plate data.

ALPR Accountability and Transparency

In 2015, the California legislature passed S.B. 34, legislation designed to enhance accountability and transparency in ALPR usage. This bill mandates that ALPR users implement data protection measures, maintain access logs, hold public meetings prior to initiating an ALPR program, establish usage and privacy policies, and keep detailed access logs. The law also restricts public agencies from selling, sharing, or transferring ALPR data, except to other public agencies.

EFF has mobilized volunteers to collect ALPR policies from agencies across California and to publicly identify agencies that are not complying with the law. EFF has also independently filed public records requests with numerous agencies to shed light on their ALPR data usage through its Data Driven and Data Driven 2 projects.

In 2019, EFF successfully advocated for a California State Legislature audit of law enforcement agencies’ compliance with S.B. 34. The subsequent report by the California State Auditor substantiated many of EFF’s concerns, revealing that agencies were not adhering to the law, lacked adequate policies, and were sharing data too broadly.