Prior to building a line, to estimate capacity, it is based on the population of the cities. If building between two cities, it is just the population multiplied by 2.

If building a route between "n" cities, then it is the sum of the population of all cities divided by the base2 log(n) - the logic here is that the citizens are equally likely to travel between 2 and n stops.

Once a line is operation, it uses the API, and counts the result of "getSimPersonsForLine", and again divides by base2 log(n) - on the basis that the citizens only travel part of the route.

To be clear, unlike with cargo (which is quite well defined), I am not sure if either of these estimates are "correct" in that it is not clear if citizens make exactly 1 trip per month etc. but I have found that these estimates seem to give about the right answer.

Thank you!