Regarding the last two, i think for me the question is, what are you trying to show me in the photos?
In the 3rd one you have the viaduct, the roof, the wood on the right each competing for the focal point without any one of them really dominating so it doesn't have a "point" to it.
The 4th is better in that the focal point is now the viaduct, is there anyway to get a view looking slightl more to the left to remove the trees on the right?
There is a good shot there if you can get to the foot of one of the arches, look straight up as close to the leg as you can.
something like this
http://k43.pbase.com/u11/kmark/upload/2503075.bDSC00734.jpg
Thats not my photo but similar to one i took a few years ago.
There is potential for a lot of good shots of the viaduct, you need to try to see it from as many angles and just keep shooting.