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.
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.