Regarding leaves, that's less of a problem for the heavy locomotives, but worth to note what helps best against the problem: brake blocks. That is: in older trains, braking was done by pressing brake blocks on the wheel's running surface itself -- with the added benefit that any slippery film attached to it from the rails was removed. That was no longer the case in modern EMUs and DMUs with their disc brakes. However, in Italy, the rail authority just prescribed the installation of brake blocks alongside disc brakes in EMUs and DMUs -- brake blocks not really used for braking.

_{*Lunatic*, n.
One whose delusions are out of fashion.}