You may have noticed that when you lay the default road in the game across a body of water , the road automatically builds a bridge across the water.
This also works at least for some player - made tram plugins !

Pause the game , use the bulldozer to demolish the road tile you want the bridge to cross , and bulldoze one tile each , each side of that road tile.
Now go to terrain , and put a water tile on the demolished road tile , and the two tiles either side of it.
Now lay your tram over the water.
It will automatically build a tram bridge.
Now go back and replace the water tile with a road tile.
You now have your tram crossing the road over a bridge.

There are probably other ways to accomplish this , but this is one trick for doing it that I have discovered.
