EXPERIMENTAL ANALYSIS AND METHODOLOGICAL APPROACH BY MICRO-SIMULATION OF CROSSING SPEED DISTRIBUTION ON ROUNDABOUTS OF SMALL AND LARGE DIAMETER

In literature many studies have shown how speed distribution in roundabouts, together with other parameters (entering flow, circulating flow, entry curvature, entry path radius, entry width, approach width, ratio of inscribed circle diameter/central island diameter, angle to next leg, etc.), can be used as a measure of safety performance for these kind of intersections. The wide use of several micro-simulation models for a preventive analysis of roundabouts performance (capacity, delays, safety, etc.) emphasizes the need for a deeper study of the most sensitive parameters for a better fitting between simulated and observed traffic conditions.This paper focuses on an experimental analysis of the through movement in two roundabouts characterized by different values of the inscribed circle diameter (D1≈1/2•D2) and located close together in the same corridor in the University Campus of Arcavacata, Italy. The main aim of the research is the suggestion of a methodological approach to the simulation process of the through movement by the use of VISSIM® micro-simulation software.Results concern the following issues: (i) coherence validation of experimental data regarding speed distributions along the through movement as a function of roundabout radius; (ii) methodological and procedural issues related to the implementation of simulation parameters in VISSIM, particularly referring to speed distributions along the crossing movement, in order to better understand the effects of the change of roundabouts geometric features on simulation results.