A　driving　simulator　was　used　to　investigate　the　effects　of　obstructive　sleep　apnea　hyperventilation　syndrome　(OSAHS)　on　a　sample　of　12　hired　drivers　(including　bus　and　taxi　drivers).　The　test　scene　was　a　two-way,　four-lane　ring　road　with　a　design　speed　of　80　km/h　in　a　free-flow　traffic　state.　OSAHS　drivers　drove　for　10　min　before　the　formal　experiment　so　as　to　become　familiar　with　the　vehicles　and　road　environment.　Then　each　driver　had　three　30-min　driving　sessions:　a　30-min　stimulus　session,　30　min　of　driving　before　a　rest,　and　30　min　of　driving　after　a　rest.　The　OSAHS　drivers　were　asked　not　to　stop　driving　except　for　major　personal　reasons.　At　the　end　of　each　driving　session,　subjects　were　asked　the　cause　of　driving　errors　and　when　they　did　not　feel　well.　OSAHS　drivers＇　driving　characteristics　(behavior)　were　studied,　such　as　their　ability　to　control　speed,　trajectory　control,　and　accident　frequency　in　the　conditions　of　the　three　30-min　driving　sessions.　The　results　showed　that　85%　of　the　OSAHS　drivers　took　measures　to　slow　down　immediately　after　being　informed　of　driving　over　the　speed　limit.　Drivers　were　driving　with　excess　speed　for　25%　of　the　total　driving　time　without　being　notified　by　a　stimulus;　they　could　feel　vibration;　and　they　could　adjust　the　wheel　to　let　the　vehicle　back　into　the　normal　lane.　Significantly　fewer　accidents　happened　after　the　rest　than　happened　before　the　rest.　The　following　countermeasures　for　these　characteristics　are　suggested　to　improve　OSAHS　drivers＇　safety　and　consequently　reduce　road　accidents:　temporary　lounges　at　service　zones,　vibration　belts　along　the　roadside,　and　speed　alarms.