Hello from France , as an architect (retired) I think it depends of the country where the bridge is installed, and if there is a risk of tornadoes... The length depends on the size of the largest ships that can navigate the channel... Otherwise a good ingineer could propose such a bridge..
I remade my bridge and scaled it back to 445ft. Which is long for 1910. Look at the smoke. This a "fixed track" asset. Isn't there a line to add to the config to fix that? Enjoy, Don