Automated License Plate Readers (ALPRs)
Submitted by New Jersey Criminal Lawyer, Jeffrey Hark.
Automated license plate readers (ALPRs) are high-speed, computer-controlled camera systems that are typically mounted on street poles, streetlights, highway overpasses, mobile trailers, or attached to police squad cars. ALPRs automatically capture all license plate numbers that come into view, along with the 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 say that the information collected can be used by police to find out where a plate has been in the past, to determine whether a vehicle was at the scene of a crime, to identify travel patterns, and even to discover vehicles that may be associated with each other. Law enforcement agencies can choose to share their information with thousands of other agencies.
Taken in the aggregate, ALPR data can paint an intimate portrait of a driver’s life and even chill First Amendment protected activity. ALPR technology can be used to target drivers who visit sensitive places such as health centers, immigration clinics, gun shops, union halls, protests, or centers of religious worship.
Drivers have no control over whether their vehicle displays a license plate because the government requires all car, truck, and motorcycle drivers to display license plates in public view. So it’s particularly disturbing that automatic license plate readers are used to track and record the movements of millions of ordinary people, even though the overwhelming majority are not connected to a crime.
How ALPRs Work
Automated license plate readers can be broadly divided into two categories.
Stationary 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.
If multiple stationary ALPR cameras are installed along a single thoroughfare, the data can reveal what direction and what speed a car is traveling. If the data are stored over time, they can reveal every time a particular plate has passed a given location, allowing the government to infer that the driver likely lives or works close by.
Stationary cameras can sometimes be moved. For example, surveillance vans or truck trailers can be outfitted with ALPR systems and then parked at strategic locations, such as gun shows or political rallies.
ALPR cameras are often used in conjunction with automated red-light and speed enforcement systems, and also as a means of assessing tolls on roads and bridges.
Mobile ALPR cameras
These 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. Also, private vendors like Vigilant Solutions capture plate data with mobile ALPRs and then sell that data to police agencies and others.
In addition to capturing images of passing vehicles, mobile ALPR cameras are effective at capturing license plates of parked cars. For example, a patrol car may drive around a public parking lot capturing hundreds of vehicles’ plates in minutes.
Most of this ALPR data is stored in databases for extended periods of time—often as much as five years. The databases may be maintained by the police departments, but often they are maintained by private companies such as Vigilant Technologies. Law enforcement agencies without their own ALPR systems can access data collected by other law enforcement agencies through regional sharing systems and networks operated by these private companies. Several companies operate independent, non-law enforcement ALPR databases, contracting with drivers to put cameras on private vehicles to collect the information. 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 agencies will often pre-load a list of license plates that the ALPR system is actively looking for—such as stolen vehicles and vehicles associated with outstanding warrants. Police officers can also create their own hotlists. If the ALPR camera scans a plate on the list, the system sends an alert to the officer in the squad car (if it’s a mobile reader) or the agency (if it’s a fixed reader). Some hotlists include low-level misdemeanors and traffic offenses. Some agencies use these hotlists to generate revenue by stopping citation scofflaws.
What Kinds of Data ALPRs Collect
ALPRs collect license plate numbers and location data along with the exact date and time the license plate was encountered. Some systems are able to capture make and model of the vehicle. They can collect thousands of plates per minute. One vendor brags that its dataset includes more than 6.5 billion scans and grows at a rate of 120-million data points each month.
When combined, ALPR data can reveal the direction and speed a person traveled through triangulation. In aggregate over time, the data can reveal a vehicle’s historical travel. With algorithms applied to the data, the systems can reveal regular travel patterns and predict where a driver may be in the future. The data also reveal all visitors to a particular location.
The data generally does not include the driver’s name. However, law enforcement officers can use other databases to connect individual names with their license plate numbers.
In addition to capturing license plate data, the photographs can reveal images of the vehicle, the vehicle’s drivers and passengers, as well as its immediate surroundings—and even people getting in and out of a vehicle. A 2009 privacy impact assessment report indicates that the photographs may even include bumper stickers, which could reveal information on the political or social views of the driver.