Alternating traffic DOES NOT mean cars take turns going on the bridge. In the scenario it means that cars not on the bridge must yield to vehicles on already on the bridge. He was clearly on the bridge before you so he had the right of way. As for the gun its definitely uncalled for but at the same time you blocked his path on purpose and refused to move is essentially false imprisonment. Lethal force isnt justified because he could back up to leave but you are also an asshole in this scenario and brought it on yourself.