title: Multi-criteria and Multi-modal Evaluation of Traffic Signal Control
Creators: name: Jiang, Wei
Publisher: name: UNSPECIFIED
Year: 2021

description: Traffic signal systems are an essential tool for traffic management in road networks. For the design of traffic signal control, it is not only necessary to address the diverse requirements from different road users but also to consider the various impacts on traffic flow quality, traffic safety, environment, and economic efficiency. However, current evaluation methods for road traffic signal control, such as the assessment of the level of service in guidelines and performance indices in optimisation methods, often evaluate from the one-dimensional perspective - mainly traffic-related aspects. Decisions made accordingly often lack a fair balance of different impacts on all road user groups. Therefore, this thesis aims to address this gap by developing an evaluation method for road traffic signal control that incorporates multidimensional criteria for various road users in a unified framework, hereby termed as "Darmstadt Method of Traffic Signal Evaluation (D-MoTSE)". Its applicability is analysed through case studies. As a basis for the method development, the basics of traffic signal control and evaluation methods were reviewed and discussed. The literature review concentrates on answering three questions: how to design a traffic signal program, which criteria and road user groups are relevant and how they are considered in the existing evaluation methods. Multiple parameters corresponding to traffic flow quality, traffic safety and environmental impacts are selected as the evaluation criteria in the developed evaluation method. The traffic-related parameters are distinguished for different traffic modes. The multidimensional evaluation criteria are first determined using appropriate simulation or calculation methods. Later on, they are converted into monetary values using established cost rates, and further aggregated to calculate the total cost. During the aggregation, particular weighting factors can be applied to reflect the political or planning preferences for specific criteria or road user groups. The cost and weighting factors can be adjusted dynamically under different situations. Superordinate effects that are of high significance at a macroscopic level can be taken into consideration as and when necessary and in the case that the relevant data are available. The developed evaluation method was applied to four individual traffic signal systems in the City of Darmstadt, Germany, as case studies. The results show that the number of persons that are present at a traffic signal system has a significant impact on the design of traffic signal control. The distribution of the related cost components differs significantly depending on the type of intersection and the traffic signal program. Furthermore, energy consumption and environmental costs take up at least one-third of the total cost, and therefore, should not be neglected in the evaluation of traffic signal control. The evaluation results can be used for comparing alternative traffic signal programs and selecting the optimum solution among them. Recommendations for designing traffic signal control can be derived accordingly. At signalised pedestrian crossings, integration into the coordination with neighbouring intersections can significantly reduce the delay costs for motorised private transport but may lead to higher costs for crossing pedestrians (and cyclists). A signal program with coordination is the optimum solution under the equal weighting of all evaluation criteria. Higher particular weight for pedestrians (and cyclists) is necessary to further reduce the delays for crossing pedestrians (and cyclists). However, it should be emphasised that generally particular weights should only be adjusted moderately in special cases with the support of plausible planning or political reasons. At signalised intersections, it can be observed that public transport priority can but does not necessarily cause disadvantages for the whole traffic. Instead, it leads to a shift of delays from public transport to other modes. The case studies revealed that no general recommendations can be provided for the design of traffic signal control at signalised intersections. The appropriate solution varies from case to case. A further implementation of the developed evaluation method in practice can assist transport engineers and authorities with the development, optimisation, revision and quality management of traffic signal control, both in the planning and operation stage. The chances and the challenges for its implementation are discussed in this thesis.