Suggestion : REAL time Passenger count (In a 49 Seater bus hardly see 12-15 passenger, this is a known idea but implementation causes game performance reduction, but can add few passengers with static other than movement as it would improve performance)
If performance is the issue: would it be impossible or too hard to put slider in preferences? Those with not-so-good computers could choose say 10% and those with high-end computers could choose 100%. 10% would mean that game tries to give number of passengers that are 10% of maximum capasity of the bus. With good computers this would mean that in some cases the bus is full and no more passengers could be taken. In other words sometimes passengers need to wait for the next bus.