Roundabouts have been continuously constructed in the U.S. in recent years, as studies have shown their capability of reducing crash risk and severity when compared with signalized intersections. Despite of the safety benefits offered by roundabouts, operational efficiency is required be analyzed when considering building roundabouts. As a prevailing simulation platform for modeling roundabouts, VISSIM have been widely applied in practice to facilitate analyzing the operational performance of roundabouts. Considering that an essential prerequisite to preparing a VISSIM roundabout model is to calibrate the model by adjusting VISSIM parameters, comprehensive calibration guidance is of great importance to practitioners. Previous calibration research has conducted qualitative analysis to study the impact of VISSIM parameters on roundabout capacity. However, parameter values based on field data and quantitative calibration guidelines are more helpful to facilitate fast and accurate modeling of roundabouts. This paper addresses these important needs. Speed trajectories of free-flow entering vehicles were collected in the field using a radar sensor. Location, length, speed distribution, and deceleration rate parameters for the VISSIM Reduced Speed Areas (RSA) were determined through the analysis of the radar data. The impact of VISSIM parameters on critical gap and follow-up headway was quantitatively analyzed through sensitivity analysis of minimum gap for PR, speed distribution and deceleration rate for RSA, and additive and multiplicative settings for the Wiedemann 74 model. Numerical guidelines for calibrating VISSIM roundabout models were ultimately developed, and validated via a case study. (Author/publisher)
Abstract