No public school bus may be operated in this State in excess of forty-five miles an hour, except when traveling on a highway with a posted maximum speed limit above fifty-five miles an hour, or when traveling to and from special events which necessitate travel on interstate or state primary highways. Special event variances from the authorized speed limit for public school buses must be obtained by written authorization from the Department of Education. In no instance may the public school bus be authorized to exceed the speed of fifty-five miles an hour. Public school buses are not required to have devices to govern the speed or operation of the vehicles.