The frequency is how long the cargo expects to wait at the station. You then need to consider how long the cargo will take to get to it’s destination (the train journey and the “walk”) and add that to the frequency. 11 minutes is too long, look at halving that. Yes, if the line is longer than 20 minutes (though 20 minutes is a decent amount of time, assuming any kind of modernish train it should be able to get anywhere in that time, not so much the earlier trains maybe) then it won’t work, try a closer industry.
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