In the Second Transport Structure plan, SVV-II, the Dutch Ministry of Transport, formulated a group of measures to exploit better the existing infra structure. For the development and implementation of traffic demand measurements the Ministry initiated a number of projects. One of these projects aims at forecasting the accessibility and congestion in the short and medium term. One special aspect within this project focuses on the development of blockages. For this project the existing assignment technique of the Dutch National Model System, QNET, has been extended. QNET, contrary to conventional assignment, aims at a more realistic way of modelling standing traffic. In QNET the link travel times are calculated using inflow restrictions when traffic is involved in a jam on preceding links. The QNET principle is further extended by enlarging the interaction between bottlenecks and the explicit modelling of blockages. The paper describes this new assignment technique QBLOK and illustrates the differences with QNET on the base of some assignments. (A)
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