Capacity Analysis of Single-Lane Roundabouts in The State of Qatar

Abstract

This master thesis presents capacity analysis of Single-Lane roundabouts in the State of Qatar. The aim of this paper is to update Qatar highway manual, by developing a new capacity model using empirical data collected from directly the field for a single lane roundabout, also to compare the obtained capacity model with the one provided by the Highway Capacity Manual (HCM, 2016). The operations of single-lane roundabouts should be studied to ensure a safe and smooth flow for road users. This study aims to analyze drivers’ behavior and estimate the capacity of two single-lane roundabouts using critical gap, entry headway gap and circulating headway gap. Video data were collected at two roundabouts located in Doha, Qatar. The analysis estimated the critical gap tc, follow up headway gap tf and circulating headway gap 𝜏 for each approach alone. Then capacity was calculated using the approach of the most critical conditions. The capacity was estimated using the Highway Capacity Manual (HCM, 2016) approach. The critical gap was different among the two sites with an average of 3.39 sec for Site 2 and 2.61 secs for Site 1. The average circulating headway gap was 2. 51 and 2.24 seconds for Site 2 and Site 1 respectively. The average follow-up headway gap was between 2.61 and 2.67 seconds for Site 2 and Site 1 respectively. The results signify that the HCM 2016 fails at higher circulating flow rates in capacity estimation in Qatar. Further, the importance of roundabouts geometry and drivers’ behavior on impacting the capacity estimation of single-lane roundabouts was reflected on the critical gap parameters.