Right-turn bypass lanes at roundabouts: geometric schemes and functional analysis

Right-turn bypass lanes can be implemented in conventional and innovative roundabout intersections to increase the capacity and improve the global functional performances. The Right-turn bypass lanes (also called slip lanes) can be distinguished according to the planimetric layout and the entry control type (stop, yield slip or Free Flow acceleration lane). This paper presents a closed-form model for the estimation of capacity, delays and level of service of roundabout equipped with Right-turn bypass lanes, considering the effect of geometric slip lane schemes, control type, vehicular and pedestrian flow. In order to examine the traffic conditions which can benefit from slip lane roundabouts in terms of capacity and delays, compared to traditional schemes which have no additional lanes, a great number of analyses have been carried out by considering different O/D matrices and vehicle and pedestrian flow vectors. Such comparisons have been made by considering the control delays in function of different O/D matrices. Such O/D matrices describe the most significant situations of traffic demand which can be of interest for the road intersections under study