LOS ANGELES (AP) — A rapidly expanding digital network that uses cameras mounted to traffic signals and police cruisers captures the movements of millions of vehicles across the U.S., regardless of whether the drivers are being investigated by law enforcement.

The license plate scanning systems have multiplied across the U.S. over the last decade, funded largely by Homeland Security grants, and judges recently have upheld authorities' rights to keep details from hundreds of millions of scans a secret from the public.

Such decisions come as a patchwork of local laws and regulations govern the use of such technology and the distribution of the information they collect, inflaming civil liberties advocates who see this as the next battleground in the fight over high-tech surveillance.

"If I'm not being investigated for a crime, there shouldn't be a secret police file on me" that details "where I go, where I shop, where I visit," said Michael Robertson, a tech entrepreneur fighting in court for access to his own files. "That's crazy, Nazi police-type stuff."

A judge tentatively denied Robertson's request under California's open records law, saying all scans are part of ongoing police investigations and that divulging them could compromise criminal cases. Arguments in the case were expected Friday afternoon.

Superior Court Judge Katherine Bacal's initial judgment comes less than a month after another state judge, using the same reasoning, denied a petition by the American Civil Liberties Union of Southern California and the Electronic Frontier Foundation for one week of records on all vehicles collected by the Los Angeles Police Department and Los Angeles County Sheriff's Department. The ACLU says that network adds 3 million scans each week to a database shared with dozens of other agencies that now includes details from more than 455 million encounters.

About 7 in 10 law enforcement agencies used license plate scanners in 2012 and an overwhelming majority planned to acquire such systems or expand their use, according to a study by the Police Executive Research Forum, a research and policy group.

Civil liberties advocates say these files need to be open to public scrutiny to prevent government overreach and unconstitutional privacy invasions.

On the other side are government and law enforcement officials who say they're not misusing the systems and that tracking and storing the data can help with criminal investigations, either to incriminate or exonerate a suspect.

"At some point, you have to trust and believe that the agencies that you utilize for law enforcement are doing what's right and what's best for the community, and they're not targeting your community," Los Angeles County Sheriff's Sgt. John Gaw said.

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Tami Abdollah can be reached at http://www.twitter.com/latams