If I may just briefly outline the way that the railway regime is structured, there are various classes of track. Depending on the speed that is desired to travel, a certain level of maintenance and quality of investment in that track is required to travel at that speed. There is a range across Canada, across various railways and railway tracks, as to what speed is planned and proposed, and therefore what level of maintenance and investment is done on that track. This becomes, to some degree, a business decision of the railway. However, if a railway is operating at any particular class level, there are a very significant set of requirements for what must be done to be able to travel at that speed.
You will see situations where, for example, a temporary repair needs to be made. At that point, it might be that the train could operate at a lower speed, so a lower track speed is applied while the repair is made, because it doesn't meet the requirements for a higher level. Then, once it's repaired, it could go back to the higher level.
In general, it's a business decision.