Testing roundabout capacity models: a practical aid for choosing the right one based on total capacity calculation

Abstract

The determination of efficiency measures, under a known traffic demand, is a central aspect of roundabouts analysis. Many capacity formulations have been available for some time in different countries relating to different roundabout layouts. This paper refers to fifteen roundabout entry capacity models used above all in the European countries, highlighting their input requirements and their algorithm complexity. The formulations reviewed are then compared referring to a test roundabout, with a simple and widespread layout. Monte Carlo simulation have been performed considering 5,000 traffic distribution matrices for each capacity model. The results obtained are critically assessed resorting to the calculation of roundabout total capacity. The probability distributions of total capacity allow finding a model that stands out among all as an advisable choice for a suitable capacity formulation, acting as a synthesis of all those examined. This can be of considerable use in view of practical applications, for the design of efficient and safe roundabout intersections in situations in which a country-specific capacity formulation is not available.