This paper describes the QBLOK traffic assignment algorithm, which has been developed from the QNET congestion-sensitive algorithm that it also describes briefly. When calculating link time, QNET allows for the inflow from preceding links, which is restricted when those links are congested. QNET also takes a heuristic approach, using a fixed number of iterations, and weights that depend only on that number. A major reason for developing QBLOK is the modelling of blockages, which cannot be considered separately from congestion. Thus QBLOK aims to: (1) improve QNET's modelling of congestion; and (2) identify blocked traffic flows and their share in the total delay caused by congestion. The calibration of QBLOK is outlined, but there are not yet enough data to allow QBLOK's validation. Some results are given for the improvement of comparable assignments, arising from the transition from QNET to QBLOK. QBLOK has now been incorporated in the Netherlands National Model as a standard assignment algorithm. It has performed well in the following application studies, giving plausible results and many insights: (1) evaluation of transport policy; (2) road user charging; (3) a `congestion atlas'; and (4) traffic management measures.
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