Abstract
The most appropriate service measure for a two-lane highway is the combination of average travel speed (ATS) and percent time spent following (PTSF). The local driver behavior and traffic operation characteristics in different countries affect the operational analysis results. The objective of this study is to evaluate the applicability of the HCM procedures on two-lane highways in Iraq. Ten highway segments in northern Iraq were selected, and more than 28,000 vehicles were observed to record traffic characteristics.
 The results show that for low flow rates, the HCM-2000 procedures tend to overestimate the ATS with an amount of 0.0085VP, while for moderate-to-high flow rates, the HCM procedures tend to underestimate the ATS with an amount of 0.0025VP for the highways considered. Moreover, the HCM procedures tend to overestimate PTSF; as well, ATS decreases as PTSF, density, and follower density increase for the highways under study. Equations are developed for the evaluation of traffic performance on two-lane highways in Iraq.
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