The National Transport University Bulletin

Abstract

The efficiency of roundabout intersections largely depends on traffic conditions at their exit sections, in particular the location of public transport stops immediately after the exit or in its vicinity, which reduces capacity and increases delays due to forced lane-changing manoeuvres and a shortage of acceptable gaps in the traffic stream. The aim of the study was to develop criteria for reducing traffic delays at the exit of a roundabout in the presence of a public transport stop, taking into account vehicle lane-changing processes and the critical gap in the adjacent traffic lane. The study was conducted using principles of traffic flow theory, methods for evaluating intersection capacity, and approaches for determining critical gaps; it was also shown that delays at roundabout exits are caused by right-lane blockage by public transport, demand for lane changing, and insufficient acceptable gaps in the adjacent stream within a local critical zone. A system of delay-reduction criteria is proposed, based on minimising total delay in the local critical zone, ensuring consistency between traffic demand and effective exit capacity, and matching lane-changing demand with the possibility of its execution under existing traffic conditions. Conditions for the transition of the traffic stream to a critical operating regime were also defined in terms of speed, density, and capacity indicators. To validate the proposed methodological approach, a computational scenario of a two-lane roundabout exit was considered. With an exit traffic flow of 1,000 veh/h, adjacent lane flow of 900 veh/h, and an average right-lane blocking time by public transport of 25 s, a lane occupancy coefficient of φ = 0.125 was obtained, resulting in a reduction of effective capacity to 1575 veh/h. Under these conditions, traffic demand does not exceed the effective exit capacity, ensuring stable traffic operation and enabling lane-changing manoeuvres without the formation of critical delays. The obtained results may be used to justify the location of urban public transport stops, determine the length of weaving sections, and select organisational and technical measures aimed at improving the efficiency of roundabout operation and reducing traffic delays

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