A system dynamics analysis of policies to relieve an urban traffic congestion problem

Abstract

In the last decade, the continual growth of air transport has resulted in overwhelming traffic congestion in most international airport access roads. This problem is a bottleneck in the development of airports which is regarded as a vital contributor to the economic sustainability of their respective cities. Many studies have been done to relieve the problem of congestion in access roads to airports. However, few of these studies have investigated the implications of these strategies on the different stakeholders in the system. In this study, a System Dynamics model is formulated to provide an understanding of some of the wider consequences of congestion-mitigating strategies in a system comprising airport access for a hypothetical city. This System Dynamics modelling approach offers an assessment platform for policy makers to study the short and long term system behaviour resulting from congestion-mitigation strategies. In particular, the implication of these strategies on the taxi industry livelihood is investigated, which besides the people involved in the industry, makes a significant contribution to an airport's business. The model is composed of three sectors: passengers and travel demand, taxis and private cars, and train. It deals with the congestion level in the road, the growth of passengers, investment in taxis, and the service availability of taxis. Simulations are performed under four policy scenarios aimed at alleviating congestion. The results indicated that, all policy interventions will have some undesirable effects on the taxi industry in terms of reduced profit and loss of jobs, each having a different level of impact. In addition, it was found that the timing of policy interventions has a significant effect on the magnitude of those outcomes. An earlier policy intervention to tackle the congestion leads not only to better conditions for the road in terms of traffic flow, but also less unfavourable effects on the livelihood of taxi drivers and operators. Accordingly, careful attention should be paid to the particular timing of policies and the timing of their implementation. The sensitivity analysis suggests that most parameters are insensitive to variations in parameters, except for one parameter; changes in this parameter had a big impact on the supply and demand for taxis and this in turn has a considerable impact on the viability of the taxi industry. The proper controlling of this variable will allow the amplitude of a shortage or surplus of taxis to be minimized. This thesis focused on certain socio-economic aspects of a transportation system and yielded insights into some aspects of the system which usually is neglected in solving transportation problems. It is hoped that the insights gained by the simulation results will lead to further understanding by decision makers about some of the wider implications of their proposals in solving transportation problems. Finally, the model in this study demonstrates the ability of System Thinking and System Dynamics methodology in the analysis of the dynamic behaviour of socio-economic systems which include complexity and multiple feedbacks