ALAMEDA -- Data collected by automated license-plate readers fitted onto Alameda police cars will be stored for six months and then purged, unless investigators are using it or think they might need it for a case, according to a draft policy on the devices that city officials are now considering.

The policy's safeguards to protect privacy include regular audits and having officers use a password-protected system so that those who have access to the information can be traced.

On Tuesday the City Council will consider spending up to $80,000 to outfit four patrol cars with three cameras each, which will register hundreds of license plates per minute on moving and parked vehicles. The collected information will include photos of the plate, GPS coordinates and the date and time the image was captured.

The license-plate readers will "give patrol officers quick and nearly effortless access to vital information about vehicles observed in public without requiring the officer to manually enter a plate number and request a database search," Alameda police Chief Paul Rolleri said in a background report for the council. "This will result in the recovery of more stolen vehicles, the apprehension of additional wanted suspects and the clearance of more crimes."

Police will prioritize using cars equipped with the technology in neighborhoods where investigators have noticed an increase in stolen vehicles and other vehicle-related crime, Rolleri said.

The council gave police the OK to seek funding for the equipment in October last year, and in February police hosted a forum at the Alameda Main Library to gather public input on the draft policy.

The forum followed police field-testing the equipment on a single patrol car last year, when the technology scanned about 97,000 plates within two weeks and scored about 85 "hits" on suspicious vehicles, police said.

The plates scanned were within about 50 feet of the patrol car and the hits included vehicles stolen in San Mateo and San Diego. Piedmont and San Leandro police are among the agencies that already use the technology.

Privacy advocates, however, note patrol cars also scan the license plates of law-abiding citizens and that unless enough safeguards are in place the collected data can be abused.

The length of time police agencies retain the data varies. The Northern California Regional Intelligence Center, which helps local, state and federal law enforcement collect and analyze information on possible criminal threats, recommends it be kept for one year. Alameda police said they are asking for a six-month retention period under the draft policy as a compromise to address privacy concerns expressed during the forum.

Alameda police applied for a federal Department of Homeland Security grant to pay for the equipment but were turned down. As a result, money that was earmarked in the 2013-14 budget to fill vacant positions that remain open would be used for the purchase.

If the council approves the proposal on Tuesday, police will purchase the devices from Vigilant Solutions, a Livermore-based company that has provided similar technology for the military, the California Highway Patrol, the Colorado State Patrol and other law enforcement agencies.

Reach Peter Hegarty at 510-748-1654 or follow him on Twitter.com/Peter_Hegarty.

IF YOU GO
The Alameda City Council will meet at 7 p.m. Tuesday in the Council Chambers at City Hall, 2263 Santa Clara Ave. in Alameda,