Local buses in mexico exit in every town and city. They do not follow the passenger number. Their local buses can actually carry as many people as they can pack inside the bus, especially during rush hour. Do not be shocked at people hanging out of the doors during peak hours in the front and back entrance of the bus. This is just normal in Mexico.

Local buses are very cheap and you actually pay when you are already on board. If you want to try their local buses and you want to get around during the day, I suggest you ride the local bus after 10 in the morning and before 4 in the afternoon.