In several instances, law-enforcement agencies restricted the public's access to these controversial records by claiming that they're part of broad, ongoing investigations. So far, courts have supported those views.
But policies on releasing license-plate recorder data are largely set by the municipality that owns the readers, and those policies can vary widely. Case in point: the Oakland Police Department has released what may be the largest set of LPR data ever seen by the public.
In response to a public-records request from news outlet Ars Technica, the department handed over more than 4.6 million records generated from license-plate readers in Oakland, CA. Those records were scanned from about 1.1 million unique license plates. The online outlet says, "the dataset is likely one of the largest ever publicly released in the United States – perhaps in the world."
On releasing the information, Oakland police captain Anthony Toribio said, "we have nothing to hide. I think it's important for a law enforcement organization to be transparent, and it goes to being credible and establishing legitimacy in the community."
That's a far different view on record accessibility than the one held by his counterpart in Los Angeles, where officials have argued millions of records are not subject to disclosure because they're part of ongoing investigations, even if the motorists whose plates are scanned are not under suspicion of any particular crime.
License-plate readers have been controversial because they're a potential threat to privacy. With enough records stored on a particular vehicle, the government could learn sensitive information about law-abiding citizens, such as where they go to church, which doctors they visit and which political rallies they attend. Depending on where scanners are positioned, law enforcement could also potentially monitor who crosses a community's borders.
Those concerns have been somewhat theoretical – without a large data set, it's hard for the public to know how the surveillance records are used and to what extent their private information may be at risk. With such a dataset now in hand, Ars Technica has shown exactly how the data can be used to sketch a portrait of an ordinary citizen's daily habits.
In a meeting with an Oakland city council member, Ars said it "was able to accurately guess the block where the council member lives after a minute of research using his license plate data." For others, the outlet could accurately predict which bar a person drank at often and where they worked.
There's fascinating detail in the story, which, if anything, should serve as a convincing reminder to motorists that if they're driving in their car, license-plate readers are one more tool being used to track their whereabouts.