2. a. Notwithstanding the provisions of any other law, rule or regulation to the contrary, no school pupil shall be allowed on board a school bus unless the bus driver or other employee of the school board or school bus contractor is also on board the bus.
b. The provisions of subsection a. of this section shall not apply when a bus driver leaves the bus to assist in the boarding or exiting of a disabled pupil or in the case of an emergency.