Assessment of Non-Recurrent Congestion on Dutch Motorways

Congestion is a problem that nowadays is facing people all over the world. It affects (in different degrees) developed countries as well as undeveloped. Congestion and queues on freeways cost money due to loss of time and therefore productivity. As a result it is considered important to assess it, in order to determine the severity of the problem faced. In the case of the Netherlands, a clear and accurate review of the causes of congestion and their contribution to vehicle loss hours is missing. For that reason, Rijkswaterstaat [RWS] proposes to investigate this topic. As a result, the main matter of this project is to differentiate diverse types of congestion. Hence the main research objective is to design a method to automatically identify the recurrent and (the most common) non-recurrent delays during single occurrences, on Dutch motorways. To achieve this objective the research question is posed: “Which part of single event delays on the Dutch motorways is caused by the following non-recurrent elements: roadworks, incidents, and adverse weather conditions?”. Besides that, the intention is to answer a set of subquestions and sub researching objectives, which are naturally related with the main research question. To accomplish these goals, it was necessary first to have a clear definition of congestion, which in this study was used travelling below a reference speed. It is also required to have a clear differentiation between recurrent and non-recurrent congestion. These are the elements that will be measured in this report. Reviewing the existing methodologies to assess different congestion, it was found that exist two main approaches to assess different congestion components: simulation-based and data driven. They both were examined in order to determine which would be the most suitable approach to be used in this study. Taking into account several factors, it was decided that the most promising approach is data driven, and thus it is the used in this report. During the checking process it was noticed some gaps in the existing methodologies to assess congestion, which are: explicit assessment of various causes of non-recurrent congestion, possibility to add in the model new causes of non-recurring congestion, different to those originally considered, lack of a structured methodology, and lack of considering network effects. Hence the new proposal fills all these gaps. Bearing in mind these facts and based on the existing methodologies, a new method was proposed to assess and to distinguish the different parts of the congestion: recurrent and non-recurrent, expressed in terms of delays. Given that the data collection process in the Netherlands uses inductor loop sensors spaced approximately 500 m, then the input data are speeds and flows measured by these sensors per motorway sections (space between these detectors) aggregated every 5 min. The remaining inputs are network configuration and databases containing time and locations of the mentioned nonrecurrent events. The outputs are the delays, classified in total, recurrent, non-recurrent with known and unknown (other) causes. The methodology was validated to show that its outcomes are realistic, and they are properly measuring the field conditions. The methodology was applied to a case study with real data. It was chosen a zone in the Randstad area including the A4, A13, A20, and A12 motorways in the Netherlands. The resulting delays data were analyzed and some conclusions were derived from the case study. It was found that in this area the A13 and the A20 present the higher congestion levels. It was also found that recurrent delays represent more than 50% of the total delays and among the considered causes of non-recurrent congestion, incidents is the one that occur more often. In addition to the goal of measuring non-recurrent delays, it was also considered the existing policies and measures created in the Netherlands to handle them. It was found that they are the result of several years of investments and developments. Therefore, the existing policies and measures to tackle non-recurrent congestion (mainly Incidents Management IM and roadworks planning) have high quality. Nevertheless it is considered that it is required further integration of the above mentioned measures with ITS services, in terms of traffic management measures and an extensive use of the providing information services. The last is especially evident in handling adverse weather conditions, as one of the considered sources of non-recurrent congestion. It was found in the results of non-recurrent delays classified as ‘other causes’ are higher than expected. Part of it is originated in bottlenecks whose cause is not among the databases. Therefore it is considered that although the quality of the existing information is high, it is still necessary more information about different kinds of occurrences, different from those considered in this study. The case study results are promising, however the developed methodology requires more data (in more motorways and considering more time) in order to derive more generic conclusions.Transport & PlanningCivil Engineering and Geoscience