You have a challenge to take some of the clinical highway look out of it and create some kinda natural woodsey look. I fear that any kind of metal or tubing might take it in the wrong direction
Just my 2cents...very nice bridge. Also I agree with Brettski.
You may want to "soften" the look with some wood. Possibly use
some versions like the pics below to slightly soften the look.
If you go with steel, I would think a dark color would be best.
Also another way to greatly soften the look if you ever so choose,
is you could make that bridge look like a "new-old" bridge by adding
the
faux stone veneers over the face of the concrete like the
bridge shown below. There are tons of choices of the stone veneers
that could make that bridge look "old" in a cool way.
