Capacity-Related Driver Behavior on Modern Roundabouts Built on High-Speed Roads

Ahmad, Shaikh.M.S.C.E.,Purdue University, December 2014.Capacity-Related Driver Behavior on Modern Roundabouts Built on High-Speed Roads. Major Professor: Andrew Tarko. The objective of this thesis was to investigate the factors that affect capacity-related driver behavior on modern roundabouts built on high-speed roads. The capacity of roundabouts is strongly affected by the behavior of drivers as represented by critical headway (critical gap) and follow-up headway (follow-up time). The effects of heavy vehicles (single-unit truck, bus, and semi-trailer) and area type (rural or urban) on roundabout capacity were investigated by comparing the critical headways for roundabouts located on high-speed and low-speed roads. The effects of nighttime conditions (in the presence of street lighting) were also considered. Data were collected using the Purdue Mobile Traffic Lab at four roundabouts built on state roads located in Indiana. The data were used to estimate a Probit model of the critical headways and their factors, as well as the follow-up headways. The findings revealed that drivers of heavy vehicles accepted critical headways that were 1.1 seconds longer than those of the passenger car drivers; on roundabouts built on high-speed roads in rural areas, drivers accepted critical headways that were 0.6 seconds longer than on roundabouts on lowspeed roads in urban areas; and in nighttime conditions, drivers accepted critical headways that were 0.6 seconds longer than in daylight conditions.