I think this is amiss: a plain concrete railway bridge for relatively narrow rivers or streams. There is already a "plain road" bridge in SC4 (or NAM) which doesn't require the road raised. All existing rail bridges must be placed at least at 30+ meters above water and this can result in very steep railtrack grades, which look awful and unrealistic. Such bridges usually have a bulky undertrack support made of concrete. There are usually no piers (just an opening in the middle) as they are supported at the two ends only. If the bridge required is longer, a few piers may be needed (they are bulky and strong too).
These bridges aren't spectacular or stylish, but they are very convenient.
I can BAT the models if needed (someone will have to explain me the "specs", ie lenghts, dimensions, LODs etc), or make some draft designs to show what exactly I mean.