Thanks for the helpful comments. What exactly is a `stroke'? Is this done with the paintbrush, a filter, or a layer effect?

For the bridges I made 2 layers of objects. The first layer was for the metal base of the bridge. I did that with the shape tool and selected a dark gray metallic color. then I bevel & embosed just slightly and added a (stock) metal texture. Then I made another layer above the metal layer, for the wood part of the bridge. I use the same layer style, except I used a wooden texture, one I found on the internet. Then I merged the two layers, did a slight Gaussian blur (no more than 2px), and played around with the opacity a bit. I also tried different blending options until I found one I liked. For these bridges I used multiply. The trick was to put the bridges below the roads layer, which I used overlay for the roads, and I copied the roads layer and for the copy I used multiply. I played around with the settings until I got what I wanted.