I noticed that most of the reports about the current Pattullo Bridge talk about this bridge needs replacing, since it's cheaper to build new instead of patching up a 70+ year old bridge. Several of the reports also mention the railway bridge east of Pattullo with suggestions to incorporate railway tracks into the new bridge.
I had another idea I had last night. Why not remove the steel portion of the old Pattullo bridge after the new Pattullo bridge is opened, but leave the old Pattullo bridge concrete piers in place so a new railway box truss can be built on them.
(original photo from Flikr)
The thickness of the line over the river is an approximation of the height that the railway box truss would need to be.
(the new Pattullo bridge isn't in the photo, since I can't find any decent drawings of any of the proposed replacement bridges)
The new Pattullo railway bridge doesn't need to be as high as the old Pattullo roadway bridge, but being built 'flat' over the old Pattullo concrete piers it should still have enough clearance for Fraser River traffic so that it doesn't need to be built as a swing-bridge, a lift-bridge or a draw-bridge. There is probably enough width on the piers to have two tracks built within the railway box truss structure, so there is a greater volume of railway traffic over the Fraser.
Building the new railway tracks right at the tops of the concrete piers will still make them substantially higher than the current railway bridge, so new viaducts on the New West and Surrey sides will need to be built to access the new Pattullo railway bridge, and they will need to be longer to reach the higher elevation, but with the higher power capacity of the railway engines today, the viaducts may be built with a higher grade than was possible last century when the current railway bridge & viaducts were built.