This　paper　studies　the　effectiveness　of　fog　warning　systems　on　driving　performance　and　traffic　safety　in　heavy　fog　condition.　A　comparison　study　was　conducted　for　four　scenarios　in　heavy　fog　condition.　First,　a　series　of　indexes　corresponding　to　driving　speed　adjustments　and　surrogate　measures　of　safety　was　obtained　to　explore　the　impacts　that　fog　warning　systems　have　on　driving　behavior　and　traffic　safety　when　approaching　a　fog　area.　This　study　divided　the　analyzed　road　into　three　different　zones　(clear　zone,　transition　zone,　and　fog　zone)　according　to　visibility　levels.　Then,　multivariate　analysis　of　variance　(MANOVA)　was　conducted,　and　the　effects　of　drivers＇　individual　characteristics　on　driving　behavior　were　also　investigated.　Moreover,　the　linear　mixed　model　with　random　effects　was　estimated　to　consider　the　contributing　factors　of　the　drivers＇　speed　adjustment　behaviors.　In　addition,　the　standard　deviation　of　speed,　TET　(time　exposed　time-to-collision),　and　TIT　(time　integrated　time-to-collision)　were　selected　to　evaluate　the　longitudinal　safety.　To　obtain　the　driving　data,　an　empirical　driving　simulator　platform　was　established　based　on　a　real-world　road　in　Beijing.　Thirty-five　drivers　were　recruited　to　participate　in　the　driving　experiment.　The　results　showed　that　the　cooperative　vehicle-infrastructure　warning　systems　could　be　beneficial　to　better　driving　behavior　and　safer　traffic　operations.　The　results　revealed　that　the　warning　systems　could　be　beneficial　to　speed　reduction　before　entering　a　fog　area.　In　addition,　the　On-Board　Unit　(OBU)　had　a　significant　impact　on　individual　speed　adjustment.　Moreover,　the　results　showed　that　scenarios　with　fog　warning　systems　improve　safety　significantly　over　the　no　warning　system　scenario.　The　study　results　could　also　facilitate　the　selection　of　a　proper　information　release　format　in　the　context　of　connected　vehicles.