Relationship between Critical Gap and Certain Geometrical Parameters in Roundabouts

Abstract

Gap-acceptance method is one of the classical methods used to analyze capacity of roundabouts. Critical gap has a privileged role in this approach. Different driver behavior and local rules of traffic has a key role in implementing it in the local standard for capacity calculation in each country. Therefore, a reliable method for estimation of critical gap at a certain location can be of great importance. This paper presents the first steps of an experimental investigation and analysis on whether it is possible to find correlation between video-based gap acceptance data and certain design parameters of roundabouts in Hungary. Ten single lane roundabouts of different size were recorded for hours in different locations in and around Budapest to assess gap acceptance data and relate it to certain design parameters like diameter, distance of neighboring entries, entry width, width of splitter island, number of entries over time, and entry angle – or any combination of those. Using only a linear approach, strong positive correlation was found between measured critical gap and distance between legs. There is correlation (not so strong however) between critical gap and (approach) entry width as well as splitter island width, and enough data were examined to say that there is no correlation between central island diameter and critical gap.

Development of Empirical Models to Predict Gap Acceptance Parameter Based on the Geometrical and Operational Parameters of Different Roundabouts

“…In this research, Raff's method was implemented to find the critical gaps values for the forty-one legs of the thirteen roundabouts. The critical gap depends on several parameters: (1) geometric design elements of roundabout (central island diameter D Island , inscribed diameter D Inscribed , width of circulatory carriageway W circulatory , entry angle E Angle , splitter island width W Splitter , distance between neighboring legs Distance Legs , entry width W Entry , and approach entry width W Approach ) [11]; and (2) Traffic volume at the circulatory roadway [12,13]. It's very important to know how the critical gap might vary based on various traffic and geometry conditions.…”

“…It's very important to know how the critical gap might vary based on various traffic and geometry conditions. Haitham and Schuchmann [11] studied the relationship between the geometric elements of ten roundabouts and the critical gaps in Hungary. They found that approach entry width (W Approach ), distance between neighboring legs (Distance Legs ), splitter island width (W Splitter ), and entry width (W Entry ) have the highest correlation with critical gap for the selected roundabouts.…”