Comparison of roundabout capacity and delay estimates from analytical and simulation models

The predictions of capacity and delay for a single lane entry stream at a single lane roundabout by two simulation models, ModelC and INSECT, and two analytical models, ARRB Special Report 45 (SR 45) and SIDRA, are compared. All these models are based on the used of gap acceptance for predicting roundabout performance. Comparisons are made for low, medium and high circulating flow levels, and for undersaturated entry stream conditions (degrees of saturation in the range 0.10 to 0.95). The features of the models in relation to capacity and delay estimation are discussed in detail. The capacities and queueing delays predicted by ModelC simulation model and the two analytical models, SR 45 and SIDRA are found to be sufficiently close given the difficulty in making the analytical and simulation model assumptions compatible. Estimates of capacity and delay from INSECT are found to be over-sensitive to the origin-destination pattern of entry flows which contribute to a particular circulating flow. They are sufficiently close to estimates from other models when a balanced arrival flow pattern is used. Capacity and delay estimates from ModelC are less sensitive to changes in the origin-destination flow pattern.