Lighting and atmo are real good.
Ivy on the tree is nice. Tunnel looks good too. Tracks also look good.
The wall on the left feels a little flat though. I think I see a bit of bump, but perhaps not as much as would be best. Displacement on the textures for the tracks rust may or may not be necessary.
Theres something a little funny with the ivy on the wall camera left.
40 hours from modeling to rendering does not sound terrible to me. If you did everything your self I would guess thats a good time.
Try rendering one in RTO off to go with your on (or the other way round) And then mask in photoshop. This method gives the most amount of control over objects displacements, for the time being.
The negatives I mentioned only apply to a still image, I think. An animation where (for example) the camera is trucking from left to right, to some other area of interest, Would look good. None of the issues I brought up would mater then. But for a still image there will always be time to find issues.
Very nice over all!