Is there a relationship between the number of trains using a track and the cost per train to use the track? That is to ask if there are more trains on the Mildura line between Maryborough and Mildura would this lower the cost of running per train?
Cost due to who? Cost to the rail operator? Cost to the track owner? Cost to government?
Have a read of this
.If the track has spare capacity for the type of train you are adding
, the answer is generally "yes" from the point of view of the "actual amount of money that has to be spent providing and maintaining the track per train".
(If the track does not have spare capacity for the type of train you are adding (which is the situation if you have a line suitable only for freight and you want to run passenger services on it) then the answer is "it depends".)
Each train that you run incurs a certain amount of additional maintenance, but there's a background fixed amount of maintenance that you need to do each period in order to simply keep the track open. So as long as each train covers at least the actual direct maintenance that it causes, there's going to be some money left over to contribute to that fixed amount.
But that saving may not be passed onto other users. For most non-mineral (and perhaps non-interstate) lines in this country, the track owner (government) loses money, and a couple of extra trains a week isn't going to change that. As a result, things tend to be structured that the access provider gets to retain the benefit of any additional revenue, up until a limit that's approximately where they stop losing money (or where some body thinks they should stop losing money - which is not quite the same thing...), beyond which they may be required to start sharing the love.
Beyond regular, occurs every year type costs, the track owner, in some cases, also may want to eventually recover some part of the upfront cost of building (or significantly upgrading, if that's happened in living memory) the line in the first place. My interpretation of the V/Line access arrangement is that it does not include this sort of provision.