From WaPo:

More than 250 cameras in the District and its suburbs scan license plates in real time, helping police pinpoint stolen cars and fleeing killers. But the program quietly has expanded beyond what anyone had imagined even a few years ago.

With virtually no public debate, police agencies have begun storing the information from the cameras, building databases that document the travels of millions of vehicles.

Nowhere is that more prevalent than in the District, which has more than one plate-reader per square mile, the highest concentration in the nation. Police in the Washington suburbs have dozens of them as well, and local agencies plan to add many more in coming months, creating a comprehensive dragnet that will include all the approaches into the District.

“It never stops,” said Capt. Kevin Reardon, who runs Arlington County’s plate reader program. “It just gobbles up tag information. One of the big questions is, what do we do with the information?”

Police departments are grappling with how long to store the information and how to balance privacy concerns against the value the data provide to investigators. The data are kept for three years in the District, two years in Alexandria, a year in Prince George’s County and a Maryland state database, and about a month in many other suburban areas.

And the Civil Liberties debate:

“That’s quite a large database of innocent people’s comings and goings,” said Jay Stanley, senior policy analyst for the American Civil Liberties Union’s technology and liberty program. “The government has no business collecting that kind of information on people without a warrant.”

But police say the tag readers can give them a critical jump on a child abductor, information about when a vehicle left — or entered — a crime scene, and the ability to quickly identify a suspected terrorist’s vehicle as it speeds down the highway, perhaps to an intended target. . .  .

It’s that precision and the growing ubiquity of the technology that has libertarians worried.

Ubiquitous surveillance? Like Omniveillance?

Orin Kerr opines:

Orin Kerr, a law professor at George Washington University who has been closely watching the Supreme Court case, said the license plate technology probably would pass constitutional muster because there is no reasonable expectation of privacy on public streets.

But, Kerr said, the technology’s silent expansion has allowed the government to know things it couldn’t possibly know before and that the use of such massive amounts of data needs safeguards.

“It’s big brother, and the question is, is it big brother we want, or big brother that we don’t want?” Kerr said. “This technology could be used for good and it could be used for bad. I think we need a conversation about whether and how this technology is used. Who gets the information and when? How long before the information is deleted? All those questions need scrutiny.”