Here's the technique to sort it by cloning Ken.
Take the image in manageable bits and just draw masks up to the edge of the viaduct as I have here. Set the clone tool fairly small and just clone from inside your mask up to the edge of the mask, cloning from as close to the edge the mask as possible to keep the tones the same. Don't forget to save it as you finish each mask. You'll be surprised how quick this is once you get the hang of it.
You'll see where I've done some cloning on the right hand side to show the difference it makes.