Even police officers must abide by the law. Many states have specific laws that apply to plainclothes police officers or officers in unmarked vehicles. Police officers in Illinois, whether state or local, must abide by the same general rules. The Illinois Law Enforcement Training and Standards Board defines an unmarked police car as a vehicle with "no distinctive identifiable marking" but it "may have portable emergency warning lights."
According to the Illinois Law Enforcement Training and Standards Board, unmarked police vehicles "may not initiate a pursuit without the authorization of a supervisor." The exception to this rule is if there is a immediate threat to life or limb if the suspect is not apprehended.
No police officer -- whether in a marked or unmarked vehicle -- can join in a pursuit in which there are already two police vehicles involved unless directed by a supervisor.
Motorcycles qualify as unmarked police vehicles. According to the Illinois Law Enforcement Training and Standards Board, a police officer in a motorcycle may initiate pursuit but "will relinquish Primary Unit status immediately upon the participation of a marked police car."
Like officers on motorcycles, officers in semi-marked cars may initiate pursuit but should yield to marked squad cars.
Police must turn on emergency lights in a high-speed situation. This law applies to both marked and unmarked police cars.