D92 Civil Engineering in Transport ORIGINAL RESEARCH ARTICLE © 2022 UNIVERSITY OF ZILINA COMMUNICATIONS 24 (2) D92-D104 MODIFICATION IN HCM DELAY MODEL FOR ROUNDABOUT FOR MIXED TRAFFIC CONDITIONS - A PILOT STUDY Asir Khan, Ashish Dhamaniya*, Shriniwas Arkatkar Civil Engineering Department, Sardar Vallabhbhai National Institute of Technology, Surat, India *E-mail of corresponding author: adhamaniya@ced.svnit.ac.in Resume Roundabouts have proven to be an effective intersection design method for smooth traffic flow movements and improved safety. Previous studies show that VISSIM, commercial traffic simulation software, can be used as a proficient tool for modeling and efficiently analyzing roundabouts. This paper focuses on developing a methodology for modeling roundabouts in India using VISSIM. Three typical roundabouts were chosen from the northern part of India. Calibration and validation of the model were performed to ensure the correctness of the model. The average delay and volume to capacity ratio (v/c ratio) were compared for developing the level of service (LOS) thresholds for Indian conditions. The thresholds are compared with existing guidelines provided by the HCM 2010 and AUSTROADS. In addition, the methodology for determining modification factors for applying HCM 2010 delay model in Indian traffic conditions is defined. Article info Received 17 September 2021 Accepted 15 December 2021 Online 10 February 2022 Keywords: roundabouts, simulation modeling, critical gap, PCU, delay, level of service Available online: https://doi.org/10.26552/com.C.2022.2.D92-D104 ISSN 1335-4205 (print version) ISSN 2585-7878 (online version) number of the standard roundabouts, which could help in understanding and analyzing traffic behavior. Hence, Simulation is widely acknowledged as one of the most effective approaches for modelling the traffic flow in heterogeneous conditions. The VISSIM is a widely used micro-simulation software that helps to model various roadway facilities. Since VISSIM imparts provision for creating links without lane discipline, the developed model can be admissible to represent Indian roadway conditions. Most discussions, related to roundabout or network modelling, call attention to the need for addressing the calibration and validation of roundabouts. Calibration can be performed by changing the conflict areas or priority rules, speed distribution and fine-tuning is attained by changing driving behavior parameters [2]. The reliability of the model thus developed is examined by validation of the results obtained from the model. Validation can be done by considering microscopic and/ or macroscopic parameters. The model used in the study has been validated using the microscopic and macroscopic parameters of the traffic flow. Performance evaluation is essential for the effectiveness of a facility. Delay can be feasibly considered as a critical performance measure of roundabouts. It is the extra time spent by vehicles before clearing the intersection. Delay results in the loss of time to the vehicle’s occupants, increased fuel consumption and additional air pollution [3-4]. This delay value considers the extra time that an average vehicle encounters 1 Introduction The presence of vehicles of various kinds with significantly diverse physical and operational features characterizes traffic in developing countries like India, which is essentially random and haphazard. Apart from that, moving vehicles might take up any convenient lateral position on the road without any regard for the lane discipline. The current state of traffic adds to the safety concerns at intersections. A roundabout may reduce delays and enable safer movements under moderate traffic conditions as the traffic flow merges and diverges at comparatively small angles and lower speeds [1]. A higher degree of safety is achieved partially due to a reduction in the speed of the vehicles entering the roundabout. Typically, at signalized intersections, vehicles waiting for the green light do not stop the engine and hence, besides safety, roundabouts provide an advantage of reduced pollution at intersections since the waiting time is comparatively very small for the entering vehicles. However, the movement of traffic and vehicular interactions at the roundabout has been a major concern to the researchers since the parameters of the traffic flow have a major impact on efficiency of any road facility. Hence, for planning safe and efficient movements, understanding the operational performance of roundabouts is essential. This warrants the need for analyzing a multitude of roundabouts in terms of geometric and traffic conditions. Developing countries like India, face challenges due to inadequate