This is a small study I have done for one of the projects I am working in. Please bear in mind that I am not a intensive blender user and usually spend little time modelling and post processing (in this particular case the total modelling time is around 3hours and ther is not posprocessing at all, image composing has been achieved using internal blender node composing).
very nice! almost photo-realistic!!! Only thing you might want to do is rotate your texture map on the pillar so that the seam is hidden from view; my eye picked up on that right away. I love the AO effect you got with the seams on the span; a detailed texture there really helps the photo-realism. And the shadow is very nice, maybe a little dark, but adds an important visual cue. Just out of curiosity, what the does the bridge look like now?
thanks for your comments. I do agree that all those hints will improve the photorealism (I will add another one myself, the ground used to simulate the shadow is far too simple and hence there is a sharp change in elevation close to the left pier, this could be improved, as well as adding bridge reflection using another alpha channel, however my time was really limited at the time of producing this models).
About the current bridge, it isnt built yet:( we are still developing alternative designs.
The mesh that your shadow is being cast upon needs more detail before it can look real.
I would consider using Photoshop or Gimp for image compositing. If you render the image into seperate passed (shadow, ambient occlusion, diffuse, specular etc.) you can make massive adjustments later and really improve the quality. A good example is the shadow beneath the bridge. You can really work on it in post-processing without the need to make a very detailed model for the ground.