What is the maximum number of folding aisle seats allowed on a bus?

The maximum number of folding aisle seats allowed on a bus is zero. This regulation is in place to ensure the safety and stability of the passengers during transportation. Folding aisle seats can pose hazards in the event of sudden stops or accidents, as they may not provide the necessary support or protection that fixed seats offer to passengers.

By prohibiting folding aisle seats, regulations are aimed at maintaining a safe environment within the bus where passengers remain securely seated throughout their journey. This also helps prevent issues related to passenger movement within the bus that could disrupt the driver's attention or create a risk of injury.

In contrast, the other options present an allowance for some folding aisle seats, which contradicts safety measures established in passenger transport regulations. Thus, having no folding aisle seats ensures better safety conditions for both passengers and drivers.