In　this　paper,　we　discuss　the　impacts　of　the　fog　warning　systems　on　driving　behavior　and　traffic　safety　under　different　fog　conditions.　Firstly,　in　order　to　obtain　the　driving　data,　an　empirical　driving　simulator　platform　was　established　based　on　a　real-world　road　in　Beijing.　The　comparison　study　was　conducted　for　eight　scenarios　which　comprise　four　warning　systems　under　fog　conditions.　Thirty-five　test　drivers　drove　an　instrumented　vehicle　eight　times,　2　fog　conditions　(light　fog,　heavy　fog)　×　4　systems　(No　warning,　Dynamic　Message　Sign　only,　On-Board　Unit　only,　On-Board　Unit　Dynamic　Message　Sign).　The　results　show　that　intelligent　warning　systems　could　be　beneficial　to　driving　behavior　and　traffic　safety.　Meanwhile,　the　vehicle-to-vehicle　warning　system　can　significantly　optimize　individual　driving　behavior.　It　is　suggested　that　proper　warning　systems　should　be　considered　for　different　fog　conditions　since　they　have　different　effect.　The　study　results　are　helpful　to　select　proper　information　release　form　in　the　context　of　connected　vehicle.　©　2019　IEEE.