Freeway incident evaluation and mitigation strategies using Intelligent Transport System

Author: Pranisha Lamichhane

Lamichhane, Pranisha, 2021 Freeway incident evaluation and mitigation strategies using Intelligent Transport System, Flinders University, College of Science and Engineering

Terms of Use: This electronic version is (or will be) made publicly available by Flinders University in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. You may use this material for uses permitted under the Copyright Act 1968. If you are the owner of any included third party copyright material and/or you believe that any material has been made available without permission of the copyright owner please contact with the details.


Freeways are the most efficient infrastructures of transportation network used all around the world for improving travel time and road efficiency. However, due to the increasing population and vehicle ownership, the traffic flow through a freeway section has also increased in recent years leading to reduction in efficiency of freeway network. This has resulted in numerous disadvantages such as increased travel times, delays, Carbon Dioxide (CO2) and Nitrogen Oxide compounds (NOX) emissions and adverse impacts on road safety. The effects of increased traffic flows are sometimes accompanied with incidents that often result in severe traffic congestion due to freeway capacity being exceeded.

This report describes the evaluation of impacts of incidents on Darlington Freeway section in Adelaide Southern Suburbs. It also covers the research for mitigation measures that could be applied in order to reduce the incident impacts through the use of Intelligent Transport Systems (ITS). Incident and ITS modelling on the freeway section in the research were conducted using microsimulation software AIMSUN. The impact of incident based on location, duration and the time of occurrence in Darlington Freeway section for different lane blockage severity (partial lane blockage and full lane blockage) has been quantified in terms of travel time, congestion, delay and emissions using the microsimulation model. The measures for reducing the incident impacts have been established using Variable Message Signs (VMS) for traffic diversion from incident occurrence area for efficient traffic incident management.

AIMSUN software was used for traffic incident modelling of Darlington Freeway section because it is a package exclusively used by the Department of Infrastructure and Transport (DIT). The base model was provided by the DIT which has been calibrated and validated in terms of section flows, travel times and queue length and found to be fit-for-purpose for the detailed freeway modelling. Several incident scenarios were modelled and the effects and consequences of each incident scenario and characteristics was established and the benefits of introducing Variable Message Signs during incident occurrence was evaluated. While diverting the traffic from adjacent routes from the freeway, the study of whole network performance is necessary to determine the impact of vehicle diversion from freeway to adjacent roads. Thus, in this research, the impact and extent of level of vehicle diversion on adjacent intersection was evaluated using SIDRA Intersection software.

Two different incident locations were studied in the northbound tunnel in Darlington Freeway for three different durations in Morning Peak of incident occurrence for the future model 2031 with different lane blockage severity levels. The results generated from incident modelling determined that full lane blockages in all cases have the highest impact on traffic performance indicators, the worst case of AM peak indicated more delay by 17.85 sec/km, increase in travel time by 15.12 minutes, queue by 212 vehicles and emissions by 6.76%, following a 15-minute incident than in normal flow conditions. Results further revealed that use of Variable Message Sign have subsequently reduced the incident impact on freeway but at the same time, the diversion of more than 30% vehicles during the worst case in AM Peak caused the whole network in the study area to reach their capacity and resulted in a complete network gridlock, vehicle

diversion exceeding 60% during non-peak time caused network gridlock. It was also observed that an incident that have short time duration and cause only one lane closure would not require any traffic diversion, even in the busiest peak hour, due to current freeway having enough spare capacity to cope with such occurrences.

The outcome of this research would be beneficial for developers and road designers to establish incident response mechanism using Intelligent Transport System for effective Traffic Incident Management in freeways.

Keywords: Incident modelling, Intelligent Transport System, AIMSUN, Variable Message Sign, Darlington Freeway

Subject: Engineering thesis

Thesis type: Masters
Completed: 2021
School: College of Science and Engineering
Supervisor: Mr. Branko Stazic