Calibration of VISSIM Roundabout Model: A Critical Gap and Follow-up Headway Approach

VISSIM roundabout models have been widely applied in practice to facilitate analyzing the operational performance of roundabouts. To prepare a VISSIM roundabout model for analysis, an essential prerequisite is to calibrate the model by adjusting parameters until real-world roundabout operations are reproduced in the simulation model. Previous calibration research has used qualitative analysis to study the impact of VISSIM parameters on roundabout capacity. Comprehensive calibration guidelines, parameter values based on field data, and quantitative sensitivity analyses of parameters are necessary to facilitate 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. Analysis identified that the approach to a roundabout entrance can be divided into four speed zones reflecting different stages of drivers’ deceleration maneuver. Location, length, speed distribution, and deceleration rate parameters for the VISSIM Reduced Speed Areas (RSA) were determined through the analysis of the radar data. Comparisons between Conflict Areas (CA) and Priority Rules (PR) were also investigated, and revealed that using PR can result in more consistent and repeatable gap acceptance behavior. In addition, 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 recommendations for calibrating VISSIM roundabout models were ultimately developed, and validated via a case study.