I analysing a segment between to point that has three lane cross section. one of these lanes acts as climbing lane or passing lane, depending on the terrain it is moving. so I want to determine it's LOS. in HCM2000 it is mentioned that three lane cross sections can not be analysed using multilane highways. and according to chaptor 20 I can not analyse this type og roadway, because this chaptor comprise roadways that has seperate climbing or passing lane. would you please to help me sincerely Ebrahim Sangsefidi ebrahim.sangsefidi@gmail.com

I see no problem in using two-lane highways method in this case. What you would have to do is to segment the analysed facility in as many sections as needed. Then, you may use the two-lane highways method for each section and direction individually, inputing the values for Lu, Lpl, Lde and Ld in each case. If you need a LOS score for the entire segment, the individual directional results can be aggregated by using the TT15 factor (page 20-29)