The　accesses　are　the　gates　of　vehicles　leaving　and　entering　into　the　road　system.　The　consistency　of　the　accesses　has　a　close　relationship　with　the　road　capacity.　The　accesses　also　have　some　impact　on　the　natural　operating　speed.　Through　the　investigation　of　the　speed　of　the　vehicles　on　the　main　lane　passing　by　the　accesses,　a　conclusion　that　they　decelerated　when　they　passed　by　has　been　made,　and　that　the　range　of　deceleration　has　a　close　relation　with　the　access　interval.　then　the　range　of　deceleration　has　been　discovered　by　computing　the　delay　of　the　vehicles.　and　finally　the　reduction　ratio　of　the　operating　speed　to　the　accesses　density　has　been　calculated.　The　conclusion　provides　a　basic　data　for　predicting　the　operating　speed　of　two-lane　highways.　©　2010　ASCE.