This limit is somewhat confusing… Is it 20 minutes in distance (distance wise from point to point) or 20 minutes in vehicle frequency? If one line with one train gives a frequency of 22 minutes, will 2 trains cut that limit in half, say 11 or will it still be 22 because of the distance.
This becomes more problematic with the industry and cargo hauling. The maps are randomly generated and in one instance i had some goods required being spawned so far from each other. No matter how many trains i added to the line, the production was still 1 for 100 years lol