A UA Police Department sergeant was arrested Saturday night on suspicion of super-extreme DUI after crashing a department SUV into a traffic sign while on duty.

Sgt. John McGrath, 27, was driving the marked vehicle when he hit a sign and cement wall on the Interstate 10 frontage road near Speedway shortly after 9:30 p.m., said Sgt. Pete Dugan, a Tucson police spokesman.

Nobody was injured.

Officers investigating the crash “noticed signs and symptoms of possible impairment” and conducted a DUI investigation, Dugan said.

McGrath was arrested on suspicion of super-extreme DUI — having a blood-alcohol content of .20 or greater — three lesser DUI charges, failure to control speed to avoid a collision and criminal damage.

McGrath was cited and released, Dugan said.

The department vehicle McGrath was driving was towed and impounded for a mandatory 30 days, Dugan said.

McGrath has worked for the University of Arizona Police Department since 2009 and was promoted to sergeant a little more than a year ago, said department spokesman Sgt. Filbert Barrera.

McGrath returned to duty about a month ago after serving a yearlong tour in Afghanistan with the Army National Guard, Barrera said.

McGrath has been placed on investigative suspension.

Contact reporter Veronica Cruz at vcruz@azstarnet.com or 573-4224.