That’s one of the photogrammetry bridges available as freeware, isn’t it?
That’s a very common problem with addon bridges since the bridge is only superimposed on the scenery and not recognized by the sim as a solid object. For the sim it’s more like a holographic projection. So you can fly through it and the cars will drive on the ground because the auto generated bridge that used to be there before is missing.
You have two possibilities:
- You take that problem up with the guy who did the bridge.
- you buy the Sydney landmarks payware addon. The bridge looks better there and the cars drive correctly.