A school activity bus is defined as a bus designed to carry __________ or more passengers.

A school activity bus is specifically defined as a vehicle designed to transport 15 or more passengers. This definition is crucial because it categorizes the type of bus under certain regulations pertaining to safety, insurance, and operational standards that are distinct from other types of buses. This ensures that the appropriate safety measures are in place for transporting students to and from school-related activities. The selection of 15 as the threshold is a standard used in many jurisdictions to help manage the safety and oversight of larger groups of children during transportation, ensuring that such vehicles meet higher safety requirements than those for smaller vehicles.