Speaking of "wet leaves on the rails"—
More than ten years ago, I was a regular commuter to Manhattan from Long Island on, what else, the Long Island Railroad.
I can remember one or two instances in the autumn when the trains were delayed due to "wet leaves on the rails". Being curious, I asked the train personnel about this and was told that the metal wheels do, in fact, lose traction on wet leaves. This means that the wheels are having a tendency to slip due to the wet leaves and therefore more power must be applied to move the train cars. I would think that when this occurs, probably the engineer would have to operate the train a bit more carefully than usual and this would result in delays and greater amounts of time to traverse the route.
Speaking about the icing conditions—
We can get pretty snowy and icy conditions in midwinter. I remember once as my train was passing through a very large junction (called Jamaica), I looked outside and said: "Omigosh, the tracks are on fire!" I had jumped to a conclusion (erroneous). It turns out that during very cold weather, there are flames generated to keep the switches from freezing. If the switches were to freeze, this would greatly delay train service.