another way
The method I use is simple, just lower the bridge slightly and run your main tracks over the top. I put spline points either side just beyond the bridge and use the Straighten Tool so your tracks fit on it neatly.
If the bridge is a viaduct and curved then lay the track beside it, get the height and set the track to that then move it/them over the viaduct.
I don't think you can straighten double track so you will need to use single. I use that all the time anyway.
Job done!
Angela