A University of Arizona 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 SUV when he crashed into a sign and struck a 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. 

At the end of the investigation, McGrath was arrested on suspicion of super-extreme DUI, for 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 UAPD since 2009 and was promoted to sergeant a little more than a year ago, Sgt. Filbert Barrera, a department spokesman said. 

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

He has been placed on investigative suspension. 

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