When are passengers allowed to stand in a moving bus?

Passengers are allowed to stand in a moving bus when the vehicle's standing passenger capacity license permits it. This is important because buses are designed with specific safety regulations in mind, including limitations on how many standees can be accommodated while ensuring their safety during transit. The standing capacity reflects the bus's design and construction, indicating the maximum number of passengers that can stand safely without compromising stability and safety during movement.

Understanding the context of the other choices helps clarify why this option is the best. While options relating to fare collection and available seating seem relevant, they don't address the fundamental aspect of safety and capacity limits. Additionally, the idea that standing is never allowed is incorrect, as many buses are specifically designed to carry standing passengers within safe limits. The key takeaway is that standing on a bus must align with the designated limits specified by the bus's standing passenger capacity license for both safety and compliance with transportation regulations.