Abstract:  

Multilane highways are highways with two or more lanes in each direction that are either undivided or divided by medians or two-way left turn lanes. Free flow speed (FFS) was adjusted to a non-ideal road condition in the Highway Capacity Manual (HCM) from the early 1990s.1 The HCM methodology for multilane highway level of service (LOS) analysis depends mainly on the FFS estimation.