Expressways　remain　the　black　spots　of　sleepiness-related　accidents.　Evidenced　by　statistical　data,　off-ramp,　as　an　inevitable　route　of　expressways,　has　the　highest　accident　rate.　Therefore,　security　issues　related　to　drowsiness　driving　on　off-ramps　appeal　to　closer　attention　and　further　discussion.　This　paper　takes　the　simulator-based　drowsiness　driving　performance　on　off-ramp　as　the　study　objective,　collecting　data　about　vehicles　running　parameters　and　22　drivers＇　manipulation　of　vehicles.　Data　were　collected　under　fully　alert　as　well　as　drowsy　conditions,　including　speed,　lateral　position,　and　steering　wheel　movements　etc.　The　results　show　that　driving　performance　on　the　off-ramp　is　significantly　affected　by　drowsiness.　The　conclusion　of　this　experiment　will　bring　a　fresh　perspective　for　further　research　on　drowsiness　driving　under　different　road　conditions.　©　2013　American　Society　of　Civil　Engineers.