However, my question remains: why do the bridges act differently, even though they are the same in construction, same price, everything?
I didn't copy the file, and I discovered this by accident: I was playing with the bridge, and copied the entire bridge off to one side to try something different. When I copied it back, it didn't work anymore, even though all the links where there and the price was the same. I am just using the copy/paste functions inside Pontifex II.
Argh! It feels like this program has something wrong with vehicles passing over bridges that I can't control with construction.