Re: As a former train driver....
Most of the Scandiwegian countries don't have large amounts of deciduous trees lining their railway tracks. Unfortunately we do; in many cases we can't remove them because either:
a) there would be a public outcry both for visual reasons and the fact that the lines would become far noisier without the tress alongside the line
b) most of the embankments would require enormous amounts of work to secure them as, in the areas where the lines are lined with trees, they are now entirely held together by root systems.
The problem is also prevalent in the Netherlands, Germany, Canada, New England and the mid-Atlantic States.
In the days when I drove trains most of the freight wagons, and indeed many of the locos and multiple units, had block brakes, which were applied to the circumference of the wheel. This roughened the wheels' surface, which in turn roughened the railhead. This meant that when leaves got between the wheel and the rail they were between two rough grinding surfaces, which quickly broke them down and allowed the trains' wheels to grip, whether accelerating or braking. The replacement of these older wagons, units and locos with newer, disc-braked ones has meant that the wheels and rails are no longer roughened in everyday use
The biggest problem with leaves on the line is a loss of braking traction, older disc-braked units tend to "pick up", meaning the entire unit is in a slide; newer units fitted with ABS (since the problem was realised and understood) require much longer braking distances, both of which mean that trains have to run at reduced speeds and greater intervals in order to allow for safe braking distances. This is why many rail operators, both here and abroad, now run special autumn timetables to allow for the safe running of trains.
Having still been driving as the phenomenon started to occur in the mid-80s I can assure you that there are few feelings more frightening than having a fully loaded 12 car unit in the evening peak, suddenly go into an uncontrollable, and at that time inexplicable, slide when applying the brakes at a station in exactly the same way you have done several hundred times before, and when you can still see the back of the next fully loaded unit beyond the next signal!