Analysing Free-Flow Speed Characteristics under Mixed Traffic Conditions

Abstract

Free-flow speed (FFS) analysis in the context of estimating capacity and road performance uses light vehicles as a reference. Under motorcycle dominated traffics however, this is considered to be less relevant.This study therefore, aims to develop models for estimating average FFS and identifying the distribution of individual FFS for each mode of transport. The important variables used for this study are vehicle types, traffic flow, and FFS which collected at three urban road links in Bali. The FFS characteristics under mixed traffic conditions are examined with two different models of speed-density and speed-flow curves. These curves are used to determine road capacity and speed reduction patterns during free-flow conditions. The FFS for motorcycle and all motor vehicles on all road segments have been found to have unimodal distributions. The differences in road geometry such as road, lane and shoulder width and the proportion of heavy vehicles, however, have no direct influence on traffic speed, density and flow during free-flow conditions. On the other hand, a large proportion of motorcycle may have an inverse relationship to FFS. The larger the proportion of motorcycle the lower the FFS. The small dimension of a motorcycle but having a large proportion on the road will influence FFS which in turn may affect the road performance.