Despite scanning millions of cars every year, the average police department in the US only matches a license plate with a car they’re looking for 0.5 percent of the time, according to a new cache of data on the use of automated license plate readers.

Police agencies across the country have been tracking the license plates of millions of drivers for years, but few people realize how widely police departments share this data, and how rarely it’s actually useful. To shed some light on the practice, the Electronic Frontier Foundation (EFF) teamed up with the freedom of information request service MuckRock to request records on the use of automated plate readers from from 200 agencies, covering more than 2.5 billion license plate scans from 2016 and 2017.

The two organizations published all of those records online Thursday for residents to see exactly how many plates are scanned by their local police, and how many other agencies are getting access to that data—in many cases, it’s hundreds of agencies across the country, many with no relation to the original agency.

“We figured the sooner we put the data out there, the sooner people would come up with innovative ways to visualize it or investigative leads,” Dave Maass, a senior investigative researcher at EFF who worked on the project, said over the phone.

Though the average “hit rate”—the number of times that scanning a license plate results in the police locating a car they’re looking for—is less than one percent, according to the database, the median number is likely lower. Maass explained that the figure is skewed by the few departments with very high hit rates. Most agencies have a much lower hit rate, sometimes as low as 0.02 percent.

One of the agencies with an unusually high hit rate was the Kansas City Police Department in Missouri. First of all, the number of license plates scanned in 2017 nearly quadrupled compared to 2016, from 9.5 million plates scanned to over 37 million. But what was also unusual was the fact that of those 37 million scanned plates in 2017, the KC police got a hit on more than 2.8 million—a hit rate of about 7 percent.

“That is a huge, huge increase in just one year,” Maass said. “That is on a whole different scale of magnitude of most other agencies, which are getting less than one percent. What is so special about the Kansas City police? How are they comprizing their hot list? What kind of people are on it, and how many?”

Also alarming, Maass said, was the number of external agencies that many police departments choose to share the data with. While some don’t share data at all, or only with local, relevant agencies, Maass compared other police departments to “a first time Facebook user who just approves every friend request they get,” sharing with hundreds of agencies, some that seem completely irrelevant.

“There was one police department in California sharing data with a police department in a town in Georgia with a population under 1,000 people,” he said. “Why does small town Georgia need big city California license plate data?”

It may seem trivial, but these license plate scanners are just another insidious form of surveillance that is unavoidable in the US today. Police are regularly recording where your car is located, storing that information for an indefinite time period, and often sharing it with numerous agencies all across the country.