Modeling　vehicle　headways,　as　a　probability　distribution　function　or　time　series,　has　been　the　focus　of　a　big　number　of　research　projects,　most　of　which　was　dealing　with　the　statistical　approach.　This　paper　presents　chaos　theory　alternative　to　the　classical　techniques.　A　quantitative　analysis　is　conducted　on　the　chaos　phenomenon　in　the　car-following　fleet　based　on　the　headway　kept　by　the　two　consecutive　vehicles　and　the　following　vehicle＇s　speed.　By　studying　the　microscopic　characteristics　of　the　vehicles　fleet　in　the　process　of　stimuli　and　reaction　it　is　proved　that　there　exists　a　chaos　occurrence　in　the　car-following　fleet.　In　order　to　reasonably　model　the　expected　headway　in　traffic　stream　four　expected　headway　models　have　been　mathematically　proposed　in　this　paper.　Then,　the　Rossler　chaos　attractor　are　introduced　in　these　four　models　in　order　to　choose　the　models　that　can　best　describe　the　actual　traffic　characteristics.　The　calibration　and　validation　procedures　are　conducted　using　high　accurate　RTK　GPS　equipped　vehicles　to　collect　data　from　expressways.　Based　on　the　results　it　can　be　seen　that　modified　headway　models　can　best　reflect　the　car-following　characteristics　of　the　real　traffic　flow.