It's likely that they won't close it until after the Castle Street works are finished, so it shouldn't be a big deal.
Must admit it is difficult to run trains on rails underwater that aren’t there through a tunnel that hasn’t been built.
The cheap tried and tested solution is to put up two posts either side of the road then hang a board/pole/or similar between the two across the road a few inches lower than the bridge, have this positioned 100 meters before the bridge.
With the decapitated heads of drivers who hit the bridge before on pikes either side, suspended above the blood guts and entrails of drivers and others responsible... Just an idea
My brother works for Su-Bridge Pet Supplies in Norfolk, and one of their drivers managed to get his truck stuck under a low bridge. No prizes for guessing what people who read the story in their local paper suggested the S U stood for.