A position responsibility related to the safe operation of mass transit vehicles including the operation of a revenue service vehicle (whether or not the vehicle is in revenue service), dispatch, maintenance of a revenue service vehicle or equipment used in revenue service, security personnel who carry firearms and any other employee who holds a Commercial Driver's License (CDL). (Refer to 49 CFR Part 655 – Prevention of Alcohol Misuse and Prohibited Drug Use in Transit Operations, Subpart A, 655.4)