The problem isn't necessarily the leaves but the cellulose that's driven out of the leaf and onto the steel rail when it's run over. Additionally, the steel whe

The problem isn't necessarily the leaves but the cellulose that's driven out of the leaf and onto the steel rail when it's run over. Additionally, the steel wheels of a train get really hot and probably turn the cellulose (and whatever else is in a tree leaf) into a pretty hard to deal with substance that coats the rail and (likely) the wheel. That makes braking difficult and can probably contribute to safety problems.