The traditional adjustment factor and the new lane interaction methods for estimating the capacity of a shared lane at a signalised intersection are discussed. The adjustment factor method is needed when the shared lane is combined with adjacent lanes into a lane group with the same departure characteristics (Highway Capacity manual method). The lane interaction method as implemented in the SIDRA INTERSECTION software employs a direct method to predict individual lane capacities without using adjustment factors. The method allows for differences in the departure characteristics of shared lanes (e.g. opposed turns and through traffic) and the adjacent lanes (e.g. through traffic only) by treating the intervals of lane blockage as effective red (lost time). This improves the prediction of not only the queue lengths and delays but also the short lane and opposed turn capacities. A generalised model of lane blockage is employed for predicting the number of departures before being blocked.
AKÇELIK, R. (1988). Capacity of a Shared Lane. Proc. 14th ARRB Conf. 14(2), pp 228-241.