Automated license plate readers

Many police and security departments around the world use techniques such as Automated license plate readers (ALPRs) to arrest criminals, find stolen cars, capture images of the license plates of passing cars to lead to investigations and many other security benefits.   

What is ALPRs

They 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 does it Work

 Automated license plate readers can be broadly divided into two categories.

Stationary 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.

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 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. 

ALPR Databases

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. 

What can it 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.