1 combination out of 362,880 (9x8x7x6x5x4x3x2) for the set of 10 different two-color subways.
To go even faster, but with a little more waiting at the start.
This assumes a set of 10 subways / trams each with 2 different colors.
It is interesting when the number of stations on the line is very large.
Enseignant Lycée Touchard-Washington Le Mans
If the subways are arranged in another combination, the frequency is not as good: risk of overtaking.
The average speed is multiplied by 1.7, the time saving is significant for travelers who stop only 2 times out of 5