PROJECT TITLE :

Comparative study on the capacity of a signalised roundabout

ABSTRACT:

Traffic signal control at roundabouts is proved to be effective in addressing significant traffic. However, the applicability of a signalised roundabout, especially compared with a signalised intersection, in terms of capability has not been investigated. For signalised roundabouts, unsignalised roundabout capability models as well as gap-acceptance theories and regression models don't seem to be applicable. This study first introduces a shockwave-based model to capture the impacts of signals at circulatory lanes on queuing and clearance time of left-turning vehicles. On this basis, a general signal timing model and a capacity model are developed. A sensitivity analysis is then elaborated to test how temporal and spatial parameters affect the capability of a signalised roundabout. Capability comparisons are created among signalised roundabouts, unsignalised roundabouts and signalised intersections. The results show that (i) underneath high traffic demand, a signalised roundabout outperforms an unsignalised roundabout; (ii) a signalised roundabout achieve higher capability than a signalised intersection will beneath bound condition, (iii) however a signalised intersection outperforms a signalised roundabout when optimal cycle length is relatively short (65 seconds during this study), (iv) capability of a signalised roundabout is terribly sensitive to the variation of signal parameters, hence care ought to be taken to design the parameters to confirm high capability.