What Is A License Plate Reader Camera (ALPR)

alpr license plate reader camera
Traffic Monitoring Cameras

Automated license plate readers can be broadly divided into two categories. Stationary ALPR cameras and mobile ALPR cameras. These are installed in a fixed location, such as a traffic light, a telephone pole, the entrance of a facility, or a freeway exit ramp. These cameras generally capture only vehicles in motion that pass within view. Mobile ALPR cameras are often attached to police patrol cars, allowing law enforcement officers to capture data from license plates as they drive around the city throughout their shifts. In most cases, these cameras are turned on at the beginning of a shift and not turned off again until the end of the shift. 

mobile alpr camera on police car

Automatic License Plate Readers or ALPR is used among US law enforcement agencies at the city, county, state, and federal levels. Over 66% of all US police departments use some form of ALPR.  ALPR is becoming a significant component of municipal predictive policing strategies and intelligence gathering, as well as for recovery of stolen vehicles, identification of wanted felons, and revenue collection from individuals who are delinquent on city or state taxes or fines, or monitoring for "Amber Alerts".

In addition to the real-time processing of license plate numbers, ALPR systems in the US collect (and can indefinitely store) data from each license plate camera. Images, dates, times, and GPS coordinates can be stockpiled and can help place a suspect at a scene, aid in witness identification, pattern recognition, or the tracking of individuals.

Automatic License Plate Readers - ALPR' s collect license plate numbers and location details, along with the exact date and time that the license plate was located. Some devices are capable of capturing vehicle make and model. They could pick up thousands of plates per minute. One vendor praises that its dataset contains more than 6.5 billion scans and rises every month at a rate of 120-million data points.

Automated license plate readers (ALPRs) are computer-controlled high-speed camera systems usually placed on street poles, streetlights, highway overpasses, mobile trailers, or connected to police squad cars. ALPRs automatically capture all identifiable license plate numbers, along with location, date, and time. The data, which includes photographs of the vehicle and sometimes its driver and passengers, is then uploaded to a central server.

Vendors suggest police may use the information gathered to figure out where a plate was in the past, to determine if a car was at the scene of a crime, to recognize travel habits, and even to locate vehicles that could be connected to each other. Law enforcement agencies may opt to communicate with thousands of other agencies about their knowledge.    

The functionality of license plate readers allows law enforcement to use many eyes and complex analytics functions. An automatic license plate reader can tell the intimate story or your travels. Using video footage, license plate readers can drastically reduce the time it takes to find a suspicious vehicle linked to criminal activity. Having a camera is like a deputy sheriff standing at the intersection where the cameras are, seeing the license plates, and immediately knowing if there's a vulnerable person, a wanted person.  

Much of this ALPR data was stored for long periods of time in databases — often as many as five years. Police departments manage the databases but they are also managed by private firms. Law enforcement agencies can access data collected by other law enforcement agencies through regional sharing systems and networks run by those private companies without their own ALPR systems. Several firms run independent ALPR systems that are non-law enforcement, negotiating with drivers to install cameras on private vehicles to capture the details. These data are then sold to companies like insurers, but law enforcement can also purchase access to this commercial data on a subscription basis.

Law enforcement authorities will also preload a list of license plates actively searched for by the ALPR system — such as stolen vehicles and vehicles registered with expired warranties. Police officers will set up their own hotlists, too. If the ALPR camera scans a plate on the list, the device will send a warning to the officer in the squad car (if it is a mobile reader) or to the department (if it is a fixed reader). Some hotlists include misdemeanors at low levels and traffic offenses. Some companies are using these hotlists to raise money by avoiding scofflaws seeking citations.

Officers may use ALPR to automatically identify or track individual vehicles in real-time by adding a license plate to a "hot list" License plates are also applied to hotlists when the car is stolen or connected with a warrant that is pending. Officers can also add a plate number to the record if the car was seen at the crime scene, the driver is a suspect in a crime, or the car is suspected to be linked to a gang. Hotlists also include crimes at low levels, too.

Since ALPRs usually collect information about everyone — not just the hot-listed vehicles — officers can scan and analyze historical data using a tag, partial tag, or physical address. For example, when a robbery occurs, an officer can enter a convenience store location to locate vehicles seen nearby. Then the officer will look up certain plate numbers and identify other places that were caught on the plate.

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