The　paper　emphasizes　that　posted　speed　limit　does　not　directly　have　impact　on　accidents.　On　the　contrary,　it　influences　traffic　safety　through　operating　speed.　Therefore,　it＇s　essential　to　explore　the　relationship　between　them.　In　this　paper,　the　conditions　of　the　same　posted　speed　limit　were　analyzed.　In　addition,　some　comparisons　between　1st-class　highways　and　2nd-class　highways　about　operating　speed　were　made.　It　can　be　found　that　posted　speed　limit　significantly　impact　on　operating　speed.　The　operating　speed　is　usually　larger　than　the　posted　speed　limit.　With　the　change　of　the　posted　speed　limit,　the　operating　speed　reduces　or　increases　accordingly.　©　2010　ASCE.