If you're looking at a project, we usually refer to the return on investment. From a purely operational point of view, when you're counting fares compared to what it costs to actually operate the system, it's what we call the RC ratio, the revenue to the cost. Right now, in Canada, on average, we're hovering at around 60%, as I mentioned. It's one of the highest ones, if not the highest, in the G-8. The transit systems here in Canada heavily rely on fares for their operations.
What is an acceptable level? Usually those are set by the local municipalities that operate or have jurisdiction over that.