Influence of Intergreen Times on the Capacity of Signalised Intersections

The quality of road traffic in urban networks is determined by the bottlenecks of the network, which are intersections in most cases. Traffic signals can provide high safety and sufficient capacity at intersections. The capacity of signalised intersections is not only determined by the geometry, layout, and stage settings, it is also influenced by the signal change intervals, when one stage ends and another begins. The interval between the ending of green of one stage or signal group and the beginning or green of another is called intergreen time. During this interval capacity reductions occur. Intergreen times are, though, needed to improve the safety. The presented research analyses the influence of intergreen times on the capacity. Another aim of the research is the promotion of an international dispute on this so far more nationally regarded topic. A thorough literature review, theoretical considerations, and empirical studies at signalised intersections in Germany highlight the improvement potential of the capacity of signalised intersections. Based on the findings, safety related research can be guided towards areas worth consideration from both a safety and capacity point of view. Such areas are, for instance, the entering behaviour of vehicles under saturated conditions, a more distinct consideration of crossing times, and the detailed appraisal of movement sequences (leading to conflicts) with their relevance for the traffic demand and their impact on the capacity. The research not only provides a detailed description of the traffic flow during signal change intervals, but also provides a model for the assessment of intergreen times with reference to the capacity. An application of this model to an example intersection gives a quantitative estimate of the improvement potential of intergreen times: the effective capacity of this signalised intersection is 7% greater than the capacity according to the German Highway Capacity Manual (HBS 2001); the capacity – without further evaluation of the safety impacts – could be improved at maximum by more than 1000 vehicles per hour. Further research into intergreen times is consequently highly recommendable.

Schriftenreihe des Instituts für Verkehr ; 24

Schriftenreihe des Instituts für Verkehr ; 24