A little noticed surveillance technology, designed to track the movements of every passing driver, is fast proliferating on America’s streets. Automatic license plate readers, mounted on police cars or on objects like road signs and bridges, use small, high-speed cameras to photograph thousands of plates per minute.

The information captured by the readers – including the license plate number, and the date, time, and location of every scan – is being collected and sometimes pooled into regional sharing systems. As a result, enormous databases of innocent motorists’ location information are growing rapidly. This information is often retained for years or even indefinitely, with few or no restrictions to protect privacy rights.

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In July 2012, ACLU affiliates in 38 states and Washington sent public records act requests to almost 600 local and state police departments, as well as other state and federal agencies, to obtain information on how these agencies use license plate readers. In response, we received 26,000 pages of documents detailing the use of the technology around the country. Click on the map icon on the right to learn how police in your state use license plate readers to track people's movements.