As exemplified by the shooting of Indianapolis police Officer David Moore over the weekend, traffic stops are one of the most dangerous duties of police officers.Moore was shot three times as he approached a car he had pulled over on Sunday morning, leaving the officer in critical condition at Wishard Memorial Hospital.Training experts with Indianapolis police and Indiana State Police said Monday that officers encounter the unknown every time they pull over a vehicle, 6News' Rick Hightower reported.On average, about 25 officers are killed each year while trying to conduct a traffic stop. Most are either shot or hit by a passing vehicle.While training can prepare an officer for what they might encounter, each situation is unique.Moore was well-trained and served as a field training officer himself, but his superiors said that no amount of training can prepare an officer for what a person in the vehicle they pulled over might do."Either you know it's high risk or you don't know what the risks are, which would imply that you don't want to let your guard down and become complacent when doing any kind of traffic stop," said IMPD Deputy Chief Lloyd Crowe, who is in charge of training for the department.IMPD and ISP said there is no perfect protocol to follow and that a lot is left up to the officer's discretion to determine how best to approach a stopped vehicle."The officers are trained to be very vigilant and watch what's going on inside the car as they're making the stop as the person pulls over to the point where they're approaching the vehicle," Crowe said.The actions of the driver play a key role in determining how an officer approaches each stop."Roll the window down. Put both hands on the steering wheel and that lets the officer know you're trying to not be a threat," said ISP 1st Sgt. Dave Bursten.Moore entered the license plate of the vehicle he stopped into his computer before exiting the patrol car, but he still may not have known the car was stolen, police said.IMPD and ISP said computer glitches sometimes keep officers from immediately knowing the status of the vehicle involved, one of the reasons there's no such thing as a routine traffic stop."Sometimes you can run a plate, and before you get the response, the person does something you don't expect," Bursten said.IMPD and ISP said protocol is to call for backup if an officer suspects a felony crime, such as a stolen car.Bill Owensby, president of the Fraternal Order of Police, said it's likely Moore did everything by the book."I'm absolutely convinced that he was just involved in something that he did everything right and it still went wrong," he said.Owensby said he considers IMPD one of the best trained departments in the country.