The plant is a vertical structure that, I think, balances the composition.
The detail below shows the line work. It is easy to get overwhelmed with all the bits of stuff, so I try to draw the major elements with a pencil and then paint in the rest of the detail as I go. It is best to step back and squint a lot to get just the essence of the details.
As I was scouting this scene, there was an angry voice coming from across the tracks, up on the back. I can't remember what he said exactly, but it was something like "What are you doing?!". I could not see him, so I imagine him to be a troll living under the bridge.