Percent　Time-Spent-Folio　wing　(Percent　Time　Delay)　is　an　important　index　to　estimate　Level-of-Service　of　tow-lane　highways.　Vehicles　traveling　at　headways　of　less　than　6　seconds　may　be　taken　to　be　followers　on　two-lane　highways　in　China.　Through　the　analysis　using　data　of　headway,　speed,　and　other　characteristics　from　interrupting　traffic　flow　on　a　highway　on　mountainous　areas,　the　relationship　between　delay　headway　and　speed　dispersion　differs　from　that　of　on　level　areas.　The　paper　advises　not　to　adopt　the　Percent　Time-Spend-Folio　wing　as　the　index　of　measuring　the　LOS.　And　the　result　can　provides　some　useful　data　to　the　study　of　highway　capacity　about　tow-line　highways　on　mountainous　areas.