A Generic Method for Comprehensible and Maintainable Operational Integrated Network wide traffic Management

Abstract

This thesis focuses on the subject of Dynamic Traffic Management (DTM) in countering traffic problems in the Netherlands, which comprises traffic control based on the real time traffic situation. Currently, most DTM measures (e.g. traffic signals, route information, ramp meters) function in an isolated manner, which limits its effectiveness from network perspective. More effective traffic management can be obtained when measures are instructed in a coordinated and integrated way, which is referred to as Integrated Network Management (INM). The method of ‘Sustainable Traffic Management’ (STM; in Dutch: GebiedsGericht Benutten) is already available to help joint road authorities to translate strategic policy goals to tactical control objectives, so control can be arranged in a harmonious way. A good method that uses these tactical control objectives for operational traffic management was however still l experienced to be lacking, which led to the following project objective for this thesis: Creating a generic method for comprehensible and maintainable operational traffic management in an urban or regional network, based on the tactical specifications as described in the STM method. Here comprehensibility refers to the clarity of the link between traffic situation and control actions. For road authorities it is vital that this link is obvious and the method does not function like a blackbox, since they are responsible for the consequences. The maintainability refers to the resulting effort to adapt the method when the availability of measures, infrastructure or policy is changed. Literature shows that currently available methods for INM have a limited comprehensibility and maintainability. It is furthermore found that the concept of rule?based control offers the best basis for a control method that can overcome these problems. The STM method already provided some relevant elements, which serve as input for the proposed method. This concerns: o Preferred and alternative routes for important OD?relations o Road priorities o Road functions o Frame of reference Furthermore three principles for operational traffic management are already available and are incorporated in the proposed method. This concerns the ‘sweet to sour´ and ´local to network wide´ control principle; they state that when countering traffic problems first restricted and local measures should be deployed, and that only when problem persist the intrusiveness and area of deployment should increase. The ‘graceful degradation’ principle furthermore states that deterioration of network elements should be strived to occur gradually. The proposed method controls traffic by giving functional instructions as output, which describe the function of a desired DTM measure, rather than its specific operational signal, facilitating a generic and maintainable method. These functional instructions consist of one of four solution directions (rerouting, enhancing throughflow, enhancing outflow or reducing inflow) and one of three control intensities. The applicability of functional instructions to relieve a network element depends on o The monitored traffic situation o STM elements (Road priorities, road functions, frame of reference and identification of preferred and alternative routes) o Network specification (defined network elements, relations between them and boundary conditions and performance insights) The proposed method uses five functioning levels (green?yellow?orange?red?black) as a representation of the state of a road, in which the road’s priority, function and reference value are incorporated, as well as its relevant network specific boundary conditions. A functional instruction is only desirable if the functioning level of the affected network elements is higher than that of the element it aims to relieve. In the proposed method an offline and an online phase are distinguished. In the offline phase, all preliminary work is done, so in the online phase only the monitored traffic situation is added as input to yield the applicable functional instructions. This offline step comprises the formation of an ‘information map’ which contains the definition of all network elements, the thresholds for the functioning levels and their mutual relations. These relations indicate which elements would be affected by a functional instruction to relieve another element. In the online phase, the functioning level of each network element is then identified, and for each deficient network elements the desirability of the functional instructions to relieve it is determined. Depending on the availability of measures and a standard order of functional instructions (in which the three control principles come forward), the applicable functional instructions are selected. The applicable functional instructions can eventually be translated to operational signals to the DTM measures. It is evaluated that the proposed method indeed offers a comprehensible and maintainable way of operational traffic management, better than the methods for INM already available in literature. Eventually it is concluded that with the proposed method now a method for INM is available that is useful for application in practice within a short time span and yields various advantages compared to the methods for INM currently used in the Netherlands. The proposed method offers a good followup to the STM method by translating the provided tactical control objectives to operational deployment of measures.