I wonder, what does this graph shows? How is free capacity calculated exactly? It usually just gives a very large number, which I have no idea what it means.
It show how much that line could be transporting if working always on 100% in all travels.
If I'm not wrong.
how much of what, though?
when does it count a new "free seat"? between every two stops, I suppose?
Either way, I think it's not very relevant. I can't see a good way to deduce actual line usage from this without complicated calculations?
I will put a request to maybe replace this with some average percentage.
I contrast the graph to Trips. If you have a train going 100% full one way, and empty the other (typical for vehicles carrying raw materials), Trips and Free capacity will be equal.
hmmm that would make sense, but there's a problem: there could be a different number of trips made on the same journey, even when it is constantly 100% full. For instance, a convoy of 50 seats which is 100% full going A-E, can do it with 50 trips each way, or with 200 trips (if all pax get off and are replaced by other pax at each intermediate stop).
So if this hypothetical convoy were 0% full on the one way trip, would we count 200 free capacity, or 50? 200 is the answer.
Another problem with this method, is that you can have different distances between pairs of stops, while they are treated equally for the free capacity purpose. For instance, a line has some stops in a city, then going to another city and has some stops there. So if it were full inside the cities, but empty between them, it would register as mostly or almost completely full (depending on the number of stops inside the cities), while in fact it was mostly empty. So considering this, the data in the free capacity graph is hardly relevant at all.
edit: I found out that indeed a free seat is registered between each two stops. I still don't know how to compare this to the number of trips - if this is even possible (due to the variable number of trips on a given route, see above). For now, if I want to determine utilization, I will have to multiply load by the number of sections (stop to stop), or something like that.
"Free capacity" here is misleading, as it implies that this graph measures capacity less load. "Total capacity" would be clearer, I think.
oh. indeed misleading! Even after checking I was sure it's cap. less load. Guess I was wrong :)