Until recently our auto travels — in public — have been essentially private. Scattered individuals may have observed our locations at given moments, but the bulk of our public movements have been practically obscure. Nobody collected data in a systematic or useful way, and our movements were lost to history.

That is no longer true. Public and private entities are scanning license plates, snapping photos of our cars, and storing the times and locations where they appear. Close correlation between license plate numbers and particular drivers means that databases of mundane information about auto movements also reveal quite sensitive information about doctor and psychologist visits, business meetings, trysts, gatherings of legal advice and participation in political advocacy. License plates and cameras are, as I testified to Congress more than a dozen years ago, "Big Brother infrastructure."

License plates are a once-sensible administrative tool that today undercuts privacy. It's possible to protect privacy and administer traffic laws at the same time, but it's not going to be easy.

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Surveillance cameras are catalyzing this conversation about "privacy in public," but the root of the problem is the lowly license plate. It's an administrative tool from a bygone technological era that has new consequences in the digital age — new, strongly negative consequences for privacy.

If a law were proposed today requiring people walking on sidewalks to wear name tags, Americans would strongly reject such an attack on the freedom to move about anonymously. The trade-offs don't make sense in name-tagging because people walking have far less capacity to harm one another than people behind the wheel of cars. But the once-sensible public identification requirement for operating a motor vehicle now reveals much, much more.

Auto licensing has public safety objectives so obvious that any questioning of it causes some people to sputter. License plates allow investigation and arrest of speeders, hit-and-run drivers and bank robbers in getaway vehicles. Awareness that they can be identified probably keeps some drivers in line.

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There are few obvious alternatives to automobile licensing, so it seems like regulating surveillance cameras is the only option. But that is essentially futile. A law against snapping images of cars would be impossible to enforce, and we wouldn't want to have such rules in a free country, which strongly favors the right to record true information that is available in public spaces.

To administer auto movements on streets, look to the skies. The tail numbers of aircrafts can't be seen at the distances involved in aviation, so aircraft carry transponders that receive and reply to radio-frequency interrogation. This helps identify them on air traffic control radar. Collision avoidance systems use these radio frequency identification (RFID) systems to detect aircrafts at risk of colliding with each other.

Promiscuous RFID systems on cars would be no better, and possibly worse for privacy, than license plates. But they can be designed to respond only to qualified interrogators, such as law enforcement or other licensed vehicles. Such systems could maintain records for car owners of each call and response, allowing oversight of the use and misuse of automobile identification systems.

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Such a technology could open new avenues for driving control and law enforcement. A cleverly designed system might allow drivers to "tag" each other with likes or dislikes that cumulatively and anonymously signal good and bad behavior to drivers and authorities alike.

A badly designed system could be worse than the status quo, but replacing license plates with smartly-tailored RFID systems would permit drivers to navigate the streets of cities without feeding surveillance cameras the records that can be used for comprehensive tracking of law-abiding individuals.

State legislators should begin the transition now. The right design for auto RFID will take a good deal of planning and testing. But the best response to the undesirable privacy effects of auto surveillance is the end of the license plate.

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Jim Harper is a senior fellow at the Cato Institute. Thinking of submitting an op-ed to the Washington Examiner? Be sure to read our guidelines on submissions for editorials, available at this link.