What kind of bridge? and where is your pike supposed to be located? US railroads in the northeast seemed to favor black, grey or silver on metal bridges. Black or grey (primer would probably work good for this) with more rust than paint seems the most common around here
It's not the same kind of bridge but I'm sure it would work for you. At the same time CN did almost all their 'down town' bridges and highway/road underpasses in black with slogans done in white. Courtesy and Service was at least one.
Behr makes spray stain. It is available through Woodworker's Supply woodworker.com
The trestle work below was sprayed with their Jet Spray and the color of the stain was dark mahogany. They have many other colors as well. While my trestle was installed outdoors and has now weathered a bit after two winters outdoors the photo shows it as originally applied.
I favor a chemical stain that reacts with the tannin in the wood. Looks a lot like creosote treated lumber.
Don't know about using it indoors. It's just white vinegar with steel wool dissolved in it. A bit smelley in application but that fades. I usually top coat it with motor oil for weather proofing but that would not work for an indoor piece as dust would stick to it and it would look grimey in short order.