The original plan was to have a train line that would go all the way to Stewart Air Base. They nixed it because they didn't want to spend the money to build the train line under the new bridge. I think the bridge could still technically hold it but it's not part of this build.
There won't be any trains, light rail, or that commuter bus that looks like a train thing on the bridge yet, but its being built into both spans so tracks or bus lanes etc can be built easily.