Simulation-based Variable Speed Limit Systems Modelling: An Overview and A Case Study on Istanbul Freeways

Abstract

Abstract: Modern transportation systems aim at maximizing the use of available resources in a sustainable manner to deliver efficient and safe movement of traffic. Variable Speed Limit (VSL) system is one of the techniques adopted in order to improve mobility. In this study, we analyse this system using simulation techniques on a 5.2 kilometre section of Istanbul Freeway D100. Being one of the most congested cities in the world, Istanbul freeways provide an excellent opportunity to test the potential benefits of VSL systems. Latest advancements along with comprehensive literature of this field based on simulation are included in this study. Microscopic traffic simulation software VISSIM is used along with MATLAB to implement VSL algorithm based on volume, occupancy and average speed. Remote Traffic Microwave Sensor (RTMS) data is provided by Istanbul municipality which is used to calibrate VISSIM.Scenarios with and without VSL system were simulated for morning hours. It is concluded that driver compliance to VSLs is an important factor for better results. Although 100% driver Compliance Level (CL) for VSL results in significantly higher improvement in performance compared to lower compliance, it is not a practical approach therefore results at 75% and 50% CL has been discussed in this study. Evaluation of network performance is done in terms of Total Travel Time (TTT) in network along with volume, speed and occupancy. Results show reduction in TTT and occupancy level along with improvement in average speed and volume. Fuel consumption and emissions is also found to be reduced in the network indicating sustainable and environmental friendly mobility.