License plate monitoring systems

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License plate monitoring systems, also known as “automatic license plate readers,” are policies through which governments use bundles of hardware and software to monitor and record the movement of vehicles and passengers within their jurisdiction. In a governmental context, license plate monitoring systems are most often employed by law enforcement and transportation agencies. For example, law enforcement agencies often use license plate monitoring systems to search for stolen vehicles and kidnapped children, to locate people with an expired license, expired registration or overdue fees, or to identify who was at or near an area during a crime. A 2013 report by the American Civil Liberties Union said that out of every one million license plates scanned, roughly 2,000 (0.002%) are flagged, of which around 47 (0.000047%) are connected to a serious crime.[1] Separately, transportation agencies may use license plate monitoring systems to collect toll fares (sometimes in connection with automated traffic light camera enforcement systems), enforce parking time limits, and analyze traffic patterns. Objections or challenges to license plate monitoring systems often rest on privacy grounds, arguments of unlawful searches, and assertions that they are disproportionately used in areas that target minorities and low-income residents.

From a technical perspective, license plate monitoring systems work by using cameras to record and log the license plate numbers of still or moving vehicles in range of the cameras. Camera systems may be permanent installations or portable systems, and may use both natural and infrared photography in order to capture data during the day and at night. Once recorded, images are processed through artificial intelligence software that extracts the license plate data and runs it through a database to compare it to other information already on file. Some license plate monitoring systems have alerts that are triggered when a specific license plate is identified at a location, whereas others merely log data that may only be searched under specifically authorized conditions.



Conceptual Example

A local law enforcement agency decides to invest in a License Plate Monitoring System to help combat vehicular crimes, like automobile theft and driving without a valid license. The agency purchases fifteen cameras and installs them at high-traffic areas, like intersections and highway ramps. Shortly after the system is implemented, a child is abducted by a known suspect. The law enforcement agency looks up the license plate number of the suspect and sets up an alarm on the regional license plate monitoring systems to alert them if the car passes. Other regional law enforcement agencies also agree to set up the same alert. The system is triggered when the car drives by one of the system's cameras. The police narrow their search to the area around the camera. The suspect is caught and the child is recovered. Over the course of the next 5 years, 3 additional abducted children and 35 stolen vehicles were recovered.

Specific Example

On February 24, 2017, a vehicle was stolen in Arizona. Three days later, the Paradise Valley Police Department received an alert that one of their license plate monitoring cameras had just photographed a license plate that matched that of the stolen car. Police were dispatched to the area, located the car, pulled it over, arrested the driver, and recovered the car. [2]

The New York Metropolitan Transportation Authority is unrolling a $500 million capital plan to install automatic toll collection on all tolled bridges and tunnels in New York City. Cameras are installed to photograph the license plates of all passing vehicles. The license plate is used to look up the vehicle's registration. The bill for the toll is then mailed to the address found on the vehicle's registration. During a two-year pilot program on the Henry Hudson Bridge, only 6 percent of drivers received a bill for the toll through the mail (the rest of drivers used another system, like E-ZPass). Only two-thirds of those mailed bills were paid, but Governor Andrew Cuomo said that penalties have made up for the loss. Accidents on the Henry Hudson Bridge were reduced by 80 percent compared to before the automatic tolls were installed. Eliminating all toll booths in New York City is expected to save one million gallons of gas and $2.3 million per year. The program is also expected to reduce commute times and carbon emissions from vehicle use, but more studies are needed to determine the amount. [3] [4]



Tradeoffs of implementing this policy may include:

  1. Decreased citizen privacy: When time, date, and location information are collected repeatedly and stored in a database, it is possible that anyone with access to the data can coax out personal information, such as daily habits, or other sensitive information, such as religious affiliation, participation in political protest, and medical visits. Dissemination of this information, whether on purpose or on accident, could cause harm to citizens, up to and including death (e.g.: domestic abusers using the data to find where their victims are hiding). There is no limit to the negative implications associated with the release of the data collected by license plate monitoring systems.
  2. Increased government surveillance: By increasing surveillance of public space, the surveyors (often government agencies) increase their power over the surveyed. This increases the possibility for citizens' rights to be infringed upon. The technology is also being used to police a growing number of activities, which could lead to further infringement of rights and/or an increase in resistance from the population it is used against.
  3. Increased warrantless searching: license plate monitoring systems can be used to track anyone without a warrant. This decreases citizens' privacy and could contribute to First Amendment "chilling effects," meaning citizens may be discouraged from exercising their First Amendment rights due to a perceived possibility of negative consequences.
  4. Increased bias in law enforcement: If license plate monitoring systems are disproportionately used on or in connection with other law enforcement tools biased toward certain populations, the technology may exacerbate systematic bias in policing.
  5. Decreased employment among toll collectors and parking lot attendants (if the technology is used to replace enforcement activities currently undertaken by paid employees)
  6. Potential for an increased number of lawsuits against the agency or organization that owns or operates the license plate monitoring system: Due to privacy-related concerns associated with license plate monitoring systems, any agency that uses this technology opens itself to lawsuits relating to how the technology is used and how its data is stored.
Compatibility Assessment

Compatibility Assessment.png

If answered yes, the following questions indicate superior conditions under which the policy is more likely to be appropriate:

  1. Are there limits to the use of data collected by the system?
  2. Are there limits to who can access the data collected by the system?
  3. Are there limits to who the collected data is shared with?
  4. Are there limits on how long collected data is stored?
  5. Are there adequate security protections on all stored data to prevent hacking and leaking of data?
  6. According to the law, do public agencies has the authority to collect data using these systems?
  7. According to the law, can the data collected by these systems be used as evidence in local courts?
  8. Is there a system of independent oversight that can ensure these systems are not used to target minority or at-risk populations?
  9. Is there enough vehicle-related crime or security-sensitive locations to justify a costly system, human employees to monitor the system, and continual upkeep and updating?


Assuming that a jurisdiction has decided to adopt the policy, the following questions will need to be answered when determining how to implement this policy:

  1. What crimes will the license plate monitoring system be used to police?
    1. There are many types of vehicle-related and non-vehicle-related crimes. Some advocacy and civil rights groups oppose using license plate monitoring systems for minor crimes and crimes that are punished with civil fines on the grounds of privacy invasion, discrimination against minorities, and the disproportionate enforcement against at-risk groups. Less controversial uses of the technology include toll collection and recovery of stolen vehicles and kidnapped children.
  2. What regulations will apply to the storage, security, access and use of data?
    1. Various questions that may need to be answered include: How long will data be stored? Where will data be stored? How with the security of data be ensured? Who can access the data? Who can data be shared with? What systems will be implemented to prevent unlawful access and ensure compliance with access laws? How will individuals be able to learn, if at all, what data has been stored about their license plate? How will the privacy of innocent drivers and passengers be protected? How will the operating agency treat data related to a flagged license plate versus data related to a non-flagged license plate? What limits will be implemented to regulate how the data is used against people in court?
    2. The longer data is stored, the greater the chance that data will be used for unintended or illegal uses. Advocacy and civil rights groups recommend storing data not connected to a crime for no more than 30 days and storing data connected to a crime for no more than 2 years. They also recommend that all data is encrypted and stored on secure servers. Cyber security experts disagree on what constitutes "secure" servers, but nearly unanimously agree that data should be encrypted.
    3. In an example of the risks of data access, former police officer Daniel Holtzclaw accessed police systems with the explicit intent to search for women that fit a certain profile that hinted they were susceptible to abuse, and then he used that information to select victims and track them to ensure they had not turned him in.[5] Advocacy and civil rights groups recommend that agency personnel be required to complete related training before being given access to the license plate monitoring system equipment or databases.
  3. What type of public reports should be submitted by users/owners of license plate monitoring systems to promote transparency, accountability, and oversight?
    1. Advocacy and civil rights groups recommend that every agency using license plate monitoring systems should publicly publish an annual report that includes (but is not limited to) how many license plates were captured by the technology, how many unique license plates were captured by the technology, what was the accuracy rate of the license plate reader software, who accessed the databases, how many people were looked up, how was the data used, how was the data disposed of, and whether all guidelines regarding access, security, and data deletion were adhered to.
  4. Which agency or agencies will be responsible for the design and administration of the system, such as the selection of monitoring locations, installation of equipment, and maintenance and reporting on the system?
    1. Primary customers of the systems may be law enforcement agencies, whereas transportation agencies may possess greatest access to infrastructure and funding related to the installation and maintenance of such systems.




Has adoption of: Common
For governance level(s): Institution, Local, State or Provincial, and National
For area type(s): Urban, Suburban, and Rural. While these systems are most commonly used in high-density areas, they are also used in rural and low-density areas.
For issue type(s): Efficiency, Safety, and Security










  • Automatic license plate recognition. Shyang-Lih Chang; Li-Shien Chen; Yun-Chung Chung; Sei-Wan Chen. (2004) IEEE Transactions on Intelligent Transportation Systems, Volume: 5, Issue: 1. DOI: 10.1109/TITS.2004.825086. This article describes the working conditions for license plate monitoring systems and discusses the reading accuracy of the programs.
  • Automatic License Plate Recognition. Kajal A. Mandhare; Pornima P. Bagate; Prof. Shalaka Shinde. (2015) International Journal of Informative & Futuristic Research, Volume: 2, Issue: 7. This article reviews a wide variety of contemporary technologies used in different license plate monitoring systems from around the world.
  • Automatic license plate recognition using mobile device. Hung Ngoc Do; Minh-Thanh Vo; Bao Quoc Vuong; Huy Thanh Pham; An Hoang Nguyen; Huy Quoc Luong. (2016) 2016 International Conference on Advanced Technologies for Communication (ATC). DOI: 10.1109/ATC.2016.7764786. This article discusses how a License Plate Monitoring System can be used on a mobile device.
  • A Quasi-Experimental Evaluation Using Roadblocks and Automatic License Plate Readers to Reduce Crime in Buffalo, NY. Andrew Palmer Wheeler; Scott W. Phillips. (2016) This article discusses a quasi-experiment designed to test whether using license plate monitoring systems at roadblocks helped to reduce crime. Results were mixed.
  • License Plate Reader Technology: Transportation Uses and Privacy Risks. Johanna Zmud; Jason Wagner; Maarit Moran; Texas A&M Transportation Institute. (2016) NCHRP 08-36, Task 136. This article discusses how license plate monitoring systems are used, what issues they face (particularly regarding privacy issues), how the legal community feels about the systems, and best practices and recommendations for using the system.


  1. [1]. ""You are Being Tracked: How license plate readers are being used to record Americans' movements." American Civil Liberties Union. 16 Jul 2013.
  2. [2]. "Stolen vehicle recovered following license plate reader alert." Town of Paradise Valley Independent. Mar 2017.
  3. [3]. "New York State to Eliminate Cash Option for Paying Tolls." Samantha Schmidt. The New York Times. 5 Oct 2015.
  4. [4]. "Futuristic plan for NY includes LED bridge lighting in color." Verena Dobnik. The AP. 5 Oct 2016.
  5. [[5]] "Why an Oklahoma Cop's Rape Conviction is a Major Victory." Charlotte Alter. Time Magazine. 12 Dec 2015.
  6. [[6]]. Police.UK
  7. [[7]]. Ontario Provincial Police.
  8. [[8]]. Department of Homeland Security.
  9. [[9]]. New York State Division of Criminal Justice Services.
  10. [[10]]. Los Angeles Police Department.
  11. [[11]]. New York Police Department.
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