I was going to suggest Gargraves or ross track on the bridge sections but I have never seen the five rail track Bob posted. I like these a lot and think they would would great on the bridge sections.
I believe you will need to adjust the height of the bridges so the Gargraves track line up with the Fastrack. I am not sure how to connect Gargraves to Fastrack but it is not really necessary as long as you connect power/ground to the Fastrack in front and behind the bridge and to the Gargraves track in the middle.
Joe