Prince William police get license plate readers

Prince William police credit a new device that reads license plates at lightning speed with the recovery of 10 stolen vehicles, seven stolen plates and arrest of five on theft charges in the last six months.

"We've used it to assist our gangs and narcotics units … to find out who's going where," added detective Roland Mulligan in a Tuesday presentation to the Board of County Supervisors about the police department's latest equipment addition, two automated mobile license plate readers.

Called the ELSAG North America MPH-900 LPR System, the mobile form of the equipment is capable of "captur[ing] 1,500 license plate numbers and images per minute, reading all 50 states, Canada, Mexico and many Arabic characters," according to the manufacturer's Web site.

Prince William has two of these systems, purchased with seizure dollars, and plans call for the purchase of

additional units if grant applications allow. The devices are mounted atop police vehicles -- though they could also be affixed to a school bus, for example, or hidden inside of taxi cab signs --and regardless of whether the officer is driving or parked, plates are scanned and the collected numbers and letters are processed by the on-board computer system.

Within seconds, officers are alerted to a stolen vehicle or stolen plate.

Moreover, Mulligan said, the system includes a search function that allows officers to enter tag numbers to help locate a particular vehicle plate that was previously captured. The feature comes in handy for police checking for parking violators -- those who stay too long in one spot -- or even during bank robberies, he said.

"Say you have a serial bank robber," Mulligan explained, "and you capture all the tags in the area of the first robbery … then capture the tags in the

second robbery area."

Analyze the images for matching plates -- and voila, a suspect is quickly uncovered, he said.

"There are some weaknesses to the system," Mulligan said. "Not a lot, but some."

Partial plate reads sometimes give the system operator a false positive, and antique plates can't be read at all, he said. Also, weather conditions can skew readings.

"Darkness is not a problem," Mulligan said. "The only problems I ever saw were freezing rain or heavy snow obscuring the letters."

According to the manufacturer, the system works well at both patrol and highway driving speeds -- at "oncoming differential speeds in excess of 120 miles-per-hour and passing speeds in excess of 75 miles-per-hour," the ELSAG Web site reports.

The system is used extensively in the Prince George's County police department in Maryland, and by Vir-ginia's state police, Mulligan said, and to a lesser degree in Fairfax County.

Staff writer Cheryl Chumley can be reached at 703-670-1907.