Large public events often require event organizers to apply for certain permits related to public safety, traffic issues often being part of the permitting and planning process.
Under current law, all motor vehicle drivers and pedestrians must obey traffic control signals, unless directed otherwise by a police or traffic officer. There is also an administrative rule that prohibits a single flagger directing traffic in the center of an intersection, except when there is an emergency or when law enforcement is flagging.
In cities with a population of 700,000 or greater, a single flagger may direct traffic from the center of an intersection without a police or traffic officer present, if part of a traffic control plan approved by the city.