It is unlawful for any group or organization or any individual acting with the group or organization, to conduct or participate in any march, assembly, meeting, parade, or gathering on roadways unless the march, assembly, meeting, parade, or gathering is limited to numbers that, in the opinion of the principal law enforcement officer, will not obstruct pedestrian or vehicular traffic in an unreasonable manner. The principal law enforcement officer shall, within 12 hours of receiving the notice required by Section 5, inform the group or organization as to the limitation on number of persons allowed to participate.