As traffic flows continue to rise, delays at many major roundabouts are increasing. One method adopted in an effort to reduce delay and increase capacity is to signalise one or more of the entry arms. Where roundabouts require signals on most or all entries, the TRANSYT method of signal settings can be used to predict the effect of fitting signals and to find optimum signal timings. The report discusses the factors to be considered in modelling a signalised roundabout using TRANSYT. These factors include the link structure, treatment of flared approaches, estimation of saturation flows, and the use of link weighting and queue penalties to avoid blocking back and `locking up' of the roundabout. Two examples are used to illustrate the techniques described. (A)
Abstract