Stop-Line Setback at a Signalized Roundabout: A Novel Concept for Traffic Operations

This paper proposes a novel concept, stop-line setback (SLSB), aimed at enhancing the capacity of signalized roundabouts and solving the problem of unbalanced flow patterns. This method is believed to avoid wasting acceptable time gaps and therefore increase the capacity of the approach with SLSB. However, to the best of the authors’ knowledge, no analytical work and little empirical work has yet explored the impact of SLSB. To bridge this gap, the phasing scheme and an adaptive control algorithm are developed for the roundabout with SLSB. Case studies are conducted under different traffic demands to evaluate the method. The findings show that (1) in peak hours the SLSB method is useful to improve the operational performance of the signalized roundabout and solve the problem of unbalanced flow patterns; (2) the right-turning vehicle volume is the critical factor that influences the benefits of the SLSB method; and (3) the phasing scheme and adaptive signal control algorithm developed in this paper are suitable to signalized roundabouts with distances of SLSB. Based on the aforementioned findings, it is recommended that the SLSB method be applied to one or two approaches with heavier traffic loads but not all approaches, which is believed to increase the capacity and reduce the average vehicle delay of the roundabout.