Review of roundabout design parameters and development of a roundabout design guideline for Sri Lanka

Abstract

Review of Roundabout Design Parameters and Development of a Roundabout Design Guideline for Sri Lanka Roundabouts are frequently used in urban areas in Sri Lanka. There is no proper guideline to design roundabouts in Sri Lanka. Increasing traffic and use of long vehicles resulted in malfunctioning some of the roundabouts. Geometry of roundabout has great influence on operation of the roundabouts. Objectives of the study are to review the roundabout design guidelines, identify the issues in existing roundabouts and formulate a roundabout design guideline for Sri Lanka. Five major design guidelines were considered to compare the design parameters of roundabout geometry. Twenty four roundabouts spread over major cities were selected for study. Main geometric parameters of each roundabout were collected using field measurements and calibrated satellite images. Standards of local roundabouts were compared with the international roundabout guidelines. Swept path analysis was carried out on selected roundabout layout for single unit truck to determine the adequacy of entry width, circulation width, exit width and operational speed. Design parameters that need to be improved on existing roundabout were identified and suitable values for selected design parameters were proposed.