An enhanced version of arcady, a computer program which models capacities, queues and delays at all types of single-island roundabouts, is described. The program uses empirical formulae to calculate entry capacities, and time-dependent queueing equations for queue and delay calculations. The enhancements include facilities to predict geometric delays and accident frequencies and to include the effects of pedestrian (zebra) crossings adjacent to the junction; these are provided using the results of recent empirical and analaytical studies. Additionally, the flexibility of the program (now known as arcady2) has been increased, with the availability of micro-computer and interactive versions. User inputs consist of various geometric characteristics of the roundabout, and traffic (and pedestrian) demand flow information (which may be specified in a number of ways). peak periods are normally modelled and capacities, queues and delays are calculated for each entry for each of a succession of short time segments (usually 10 or 15 minutes) within the period. The user is therefore able to assess the performance of both planned and existing roundabout designs, in terms of queueing delay, geometric delay and safety. Details of the required input parameters are given, the output is described and a full example is included. (Author/publisher)
Abstract