It's not leaves on the line that are in a pile, it's leaves on the line that get smashed onto the rail, and make the already low friction rails even lower frict

It's not leaves on the line that are in a pile, it's leaves on the line that get smashed onto the rail, and make the already low friction rails even lower friction. If you can't stop and you can't go, then the railroad isn't going to take you anywhere.