I think a good way to estimate it is to get a graph where you have average number of people in a bus at a time, then compare that to the average amount of peopl

I think a good way to estimate it is to get a graph where you have average number of people in a bus at a time, then compare that to the average amount of people that are in a car at a time. people_in_bus/average_#_people_in_cars = #_of_cars_removed_at_this_moment . Of course the model can be made significantly more complicated, but it's a good starting point.