Speeding　is　one　of　the　most　prevalent　factors　contributing　to　traffic　crashes.　Speed　limit　is　one　of　strategies　to　enforce　traffic　safety　by　controlling　drivers＇　choices.　This　paper　discusses　the　rationality　of　speed　limit　on　Bosai　highway　in　Xinjiang　Province.　In　order　to　evaluate　the　rationality　of　speed　limit,　three　studies　sites　were　posted　in　vicinity　of　speed　limit　sign.　Speed　distributions　inside　and　outside　speed　limit　zone,　crashes　records　and　drivers＇　compliance　were　examined.　Significance　of　speed　differences　are　tested　by　independent　t　test.　Results　show　that　100km/h　speed　limit　for　passenger　cars　is　within　drivers＇　expectation　and　80km/h　speed　limit　for　commercial　vehicles　is　unreasonably　high.　As　to　the　safety　impacts,　there　is　no　evidence　supporting　the　relationship　between　crashes　and　speed　limit　due　to　the　limited　data.　The　checking　process　has　a　practical　aspect　for　speed　determination　and　optimal　use　of　limited　road　resources.　Copyright　ASCE　2009.