Sheriffs serve in areas that are not covered by police departments. In large police departments, officers are usually assigned to a specific duty. Some officers patrol while others direct traffic. Some officers stay at the station and work on solving crimes. These officers are experts in identifying guns, fingerprints, or handwriting.
Detectives gather facts and collect information about crimes.
Very large cities often have special units such as motorcycle and bicycle patrol or police dog handlers. State police officers patrol highways. They mainly enforce speed limits and give tickets. At accidents, they provide first aid or direct traffic. They write reports about the cause of the accident.