Assessment of non-recurrent congestion on Dutch motorways

Congestion on freeways is a growing problem that nowadays can be seen all over the world. It occurs when the vehicle demand temporarily exceeds the available capacity. Congestion and queues on freeways cost money due to loss of time and therefore productivity. Currently, there are several approaches for defining and measuring congestion delay. Nevertheless there is a lack of consistent definition and measurement of the congestion and the parts that it consists of, using real-world data. Also in the Netherlands, Rijkswaterstaat (RWS) lacks of a clear and accurate review of the numerous causes of congestion and their contribution to vehicle loss hours.

The Verkeerscentrum Nederland (VCNL) and the Dienst Verkeer en Scheepvaart (DVS) of RWS are currently insufficiently able to indicate which part of the congestion is due to demand exceeding capacity in regular conditions (recurrent congestion), and which part is caused by external additional (non-recurrent) elements. Currently RWS determines these parts of congestion based on best-practice and experience. The additional (non-recurrent) delay is mainly caused by incidents (such as accidents and breakdowns), roadworks, and inclement weather.

The consequences of congestion are mainly delays (time loss) and queues. A better understanding of them can improve for instance the traffic state prediction and thereby may improve the Traffic Management measures. When these non-recurrent elements are present they may affect some drivers’ choices such as route, departure time, and destination, among others. Therefore, it is necessary to look in a broader extent than in a road stretch to assess the impacts that those occurrences have over the network. For that reason, potential flows divert to alternative routes and changes on demand levels, when these non-recurrent elements are present, are going to be studied as well.

In light of this, the main objective of the project is to design a methodology to identify the recurrent and (the most common) non-recurrent delays during single occurrences, on Dutch motorways. Besides that, the potential effects of non-recurrent congestion on the network flows will be studied, as well as make some policy recommendations to mitigate the adverse effects of the non-recurrent congestion.

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