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A new investigation shows the scale of surveillance on U.S. highways is more extensive than many previously imagined, thanks to a license plate database that allows federal and local law enforcement to watch cars and even drivers in real time.

According to documents reviewed by the Wall Street Journal, the database was created by the Drug Enforcement Administration to track cartel activity, but it soon came to comprise millions of records that are regularly shared with police forces across the country:

The Justice Department has been building a national database to track in real time the movement of vehicles around the U.S., a secret domestic intelligence-gathering program that scans and stores hundreds of millions of records about motorists […] The DEA program collects data about vehicle movements, including time, direction and location, from high-tech cameras placed strategically on major highways. Many devices also record visual images of drivers and passengers, which are sometimes clear enough for investigators to confirm identities.

The database was created to help the DEA carry out civil forfeitures, a controversial practice that involves taking cash, vehicles and property from individuals suspected of ties to drug-related activity without basic due process. But soon all sorts of state and local law enforcement groups joined into the effort, tapping into the database for a wide variety of purposes, according to the Journal.

The high-tech cameras in question are mounted alongside major federal highways, and are reportedly augmented by various state and local license plate readers.

If the report is accurate, it represents a depressing convergence of two troubling legal trends in the United States: mass surveillance along with civil forfeiture.

While Senator Patrick Leahy (D-Vt) has concerns over the widespread use of license plate databases last year, the DEA program appears to have been subject to little political or judicial oversight.

Meanwhile, in an apparent irony, the AP also reported Monday that law enforcement agencies are objecting to the use of a popular Google-owned app called Waze, which lets motorists see road and highway conditions in real time. The police object to a feature that displays where the police are present, arguing the feature is a threat to cops.