VISTA, Calif. -- A North County public bus driver whose blood-alcohol level was more than three times the legal limit when he was on the job pleaded guilty Friday to three misdemeanors and was sentenced to an alcohol-treatment program and 90 days in custody.

David Joseph Costello, 41, had been driving for three months for First Transit, a company that took over bus operations for the North County Transit District, when he was arrested June 1.

A bus rider reported Costello was going slow and stopping at bus stops where no one was waiting, even though the bus was running late, and a sheriff's deputy stopped him on Encinitas Boulevard between Oceanside and Encinitas.

His blood-alcohol level was measured at 0.25 percent. The threshold for drunken driving is 0.08 percent, and .04 percent for commercial vehicles.

He pleaded guilty to DUI, driving a commercial vehicle with a blood-alcohol level above .04 percent and public intoxication for being drunk in public in a separate incident, said Deputy District Attorney Dan Owens.

Costello has been cited nine times since 2006 for alcohol-related offenses in North County, such as being drunk in public, according to court officials.

His parents said he has struggled with alcohol problems for years.

He is to report for custody Dec. 8, after completing a 120-day alcohol treatment program, Owens said.