In the Highway Capacity Manual (HCM) there are two factors accounting for the platooning in vehicle arrivals and filtering effect caused by the upstream signals, namely the progression adjustment factor and the upstream filtering adjustment factor. The progression adjustment factor in HCM is only described by the arrival types. Thus, in a planning scenario, the planner is not able to determine the progression adjustment factor according to the proposed traffic demand and signal timing plan. The upstream filtering adjustment factor in HCM is defined as a function only of the volume-to-capacity ratio of the upstream signal. This is not sufficient. For overcoming both problems mentioned above, some useful derivations which can be used as a default solution given the traffic demand and signal setting in a planning scenario are presented. The solution is based on a generalized model which is compatible to the existing procedure in HCM.
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