Seriously, if you look at the real thing they generally attach the wires to the bridge structure wherever convenient, or run them inside a pipe alongside or under the bridge. Simplest way to fake that is use a terminating telegraph pole that has the wires run down to the ground.
Kon: What I like to do is use the height button on each pole and place on the sides of the bridges beside the tracks..If the bridge has railings place on top of the railings..