In his letter of retirement, Officer Bradley B. Bickett apologized for his conduct.
"I offer my most sincere apologies to the Aurora Police Department, the citizens of Aurora, and all of law enforcement for this incident," he wrote, according to a police statement.
Bickett could not be reached for comment.
He and Gerald Kirby were accused of speeding past traffic with their emergency lights flashing and tossing trash from a window on their way to the South Dakota funeral of a fallen police officer.
Their squad car was pulled over Wednesday after authorities say a volunteer firefighter spotted the car driving erratically on a state highway outside Torrington, Wyo., about 50 miles northeast of Cheyenne. Bickett was charged with driving while impaired, careless driving and speeding, while Kirby was charged with littering.
Aurora Police Chief Daniel Oates thanked Bickett for leaving the department.
"It is unfortunate that a 31-year career of service in law enforcement was destroyed by a single day of poor judgment. He made the honorable choice to retire," Oates said in his statement. "His apology will mean a great deal to his colleagues in the department and will help put this unfortunate event behind us."
Kirby remains on restricted duty pending a full internal affairs investigation.
Aurora police spokesman Bob Friel said Friday that Bickett and Kirby received permission to travel to Rapid City, S.D., to represent their department at a funeral for one of two officers killed in a shootout earlier this month. Bickett knew an officer in the South Dakota department, Friel said.
Goshen County Sheriff Donald J. Murphy said Bickett's blood-alcohol level tested at 0.08 percent, the level at which he said a driver is presumed to be under the influence. Another test determined later his level was 0.077 percent, Murphy said. A beer cooler was found in the back seat.
Bickett's speech was described as "slurred" in a booking report posted on the Goshen County Sheriff's Department website. He was released on his own recognizance early Thursday.
The funeral for the fallen officer, Nick Armstrong, 27, was held Thursday. The officers never made it to the funeral. Two Aurora police officers went to Wyoming to pick up Bickett and Kirby. They were immediately placed on desk duty pending an internal investigation.
Armstrong and Officer J. Ryan McCandless were killed in an Aug. 2 shootout that erupted while they were trying to question four men walking with an open alcohol container, Rapid City police spokeswoman Tarah Heupel said. A third officer, Tim Doyle, was hospitalized with multiple gunshot wounds.