Incident management and environmental impacts in urban road networks

Vehicle delays in road networks cost not only in terms of time and money but also in terms of the environmental conditions and more especially, in terms of emissions and energy consumption. This situation becomes worse in the case of an emergency situation (e.g., road accident) where there is an immediate need for the traffic to be diverted into other roads in order to minimize the delays and the associated environmental problems. Within the framework of this paper the environmental impacts of various traffic management measures are presented when these measures are implemented in urban road networks so as to deal with emergency situations. The evaluation of the above-mentioned measures is done through the use of traffic simulation modelling techniques. The results of the examination of various parameters such as energy consumption and pollutants emitted (CO, CO2, NOx, HC, and Pb) through the use of a simulation model will be presented and discussed. The reference area is the city of Thessaloniki, which faces environmental and traffic problems especially during peak hours. The traffic simulation model that was used for the purposes of the present research was the Simulation and Assignment of Traffic to Urban Road Networks (SATURN), which is a suite of flexible network analysis programs developed at the Institution for Transport Studies, University of Leeds, UK. SATURN is a combined traffic simulation and assignment model for the analysis of traffic management schemes over relatively localised networks. SATURN is also closely linked with the ME2 Model (Matrix Estimation from Maximum Entropy), a technique that enables demand trip matrices to be estimated directly from traffic counts. The road network used in SATURN for the purposes of this research consists of 813 nodes and 293 zones. Nine (9) scenarios are examined depending on how serious the incident is (minor, moderate, major) and also depending on the traffic management measures to be taken. The use of telematics in the sense of variable message signs (VMS) operation is included in some of the scenarios. Parameters such as traffic volumes, delays, speed and the use of road network are examined, with special consideration given to the impacts of the measures on vehicle emissions and fuel consumption. The use of SATURN as a tool to assess environmental and traffic impacts is proved to be of great importance and can provide many alternative solutions to the decision makers in order to confront these problems.