Could be a stringer as that steel beam visible in the last photo is fairly heavy. And the lower joints don't look like they are connected to the stringer in a way that would carry a lot of tension load.
Conversely, the members of the truss are substantial enough, and the joints look heavy enough the truss could be carrying quite a bit of load.
But the fishplate joint for the timbers is not a very good tension joint. Not all the joints are under tension - but some are. And the compression and tension joints are built the same.
So my vote - with out making a closer inspection - is it's mostly a stringer with warren truss shaped railing.
Hmmm...
It appears to me that this bridge might be a steel stringer bridge with decorative wood truss railings, and not a structural wood truss bridge.
For what it's worth, it almost appears to me that the lower chord gussets are welded to the steel beam and bolted to the truss members, and while the beam appears to be decently heavy, it's also long enough where it would flex substantially if the truss weren't there to help with the load. I think that the steel beam is actually the lower chord for the truss, but is also a stringer since it's all one piece rather than multiple segments joined at the gussets like an actual truss lower chord would be.