International Journal of Engineering & Technology, 4 (3) (2015) 432-438 www.sciencepubco.com/index.php/IJET ©Science Publishing Corporation doi: 10.14419/ijet.v4i3.4754 Research Paper The role of optimization to control traffic signals setting on capacity and flow at peak hours at intersections Pegah Jafari Haghighatpour 1 *, Ali Mansourkhaki 2 , Gholamreza Mehdizadeh 3 ,Mahmouddreza Keymanesh 4 1 PhD Candidate in Transportation of Tehran Payame Noor University, Tehran 2 Associate Professor, Department of Civil Engineering, University of Science and Technology, Tehran, Iran 3 Master of Science, Department of Engineering, Islamic Azad University South Tehran Branch 4 Assistant Professor, Department of Civil Engineering, Tehran Payame Noor University, Tehran, Iran *Corresponding author E-mail: p.j.haghighatpour@gmail.com Copyright © 2015 Pegah Jafari Haghighatpour et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract Control the pre timing of traffic signals has many advantages because of its responsiveness to traffic demands, short cycles, and effective use of capacity leading to and recovering from oversaturation and amenability to aggressive transit priority. Traffic congestion in urban road and freeway networks leads to a strong degradation of the network infrastructure and accordingly reduced throughput, which can be countered via suitable control measures and strategies. Coordination between intersections in a central system increases capacity, appropriate traffic flow and reduce total delays of vehicles. Scats system has been installed in many world intersections, and many researchers have done about the advantages of it to decrease delays and travel times at intersection. SCATS is a modular system and development of this is possible. Now in Tehran's this system is used and traffic conditions matches on it. Traffic signal timing schedule gives in this system as default and although this system is capable of adapting to the moment traffic but in terms of super saturation and during peak hours due to the lack of optimization, default program around intersection has caused widespread congestion at intersection. In this paper, two intersections of East and West of Tehran have been selected, and in two different situations, the flow to capacity ratio of traffic signal timing has been investigated before and after optimization. Simulation by AIMSUN and optimization by SYNCHRO software is done. After optimization can be observed that if before the pre-defined schedule for SCATS, this plan for each intersection of the volume of traffic at peak hours has been optimized, a great reduction in delay and increase in capacity can be observed at intersections. For example, delay time reduction has been occurred about 14.77 in AM peak time and 12.65 in PM peak time at GOLBARG-DARDASHT intersection. Keywords: Delay; Intersection; Flow and Capacity; Optimization; Traffic Signals Setting. 1. Introduction Traffic congestion is a major problem in modern societies due to increasing population and economic activity. This motivates the need for better utilizing the existing infrastructures and for efficiently controlling the traffic flow in order to minimize the impact of congestion. Transportation has always been a crucial aspect of human civilization, but it is only in the second half of the last century that the phenomenon of traffic congestion has become predominant due to the rapid increase in the number of vehicles and in the transportation demand in virtually all transportation modes. Traffic congestion appears when too many vehicles attempt to use a common transportation infrastructure with limited capacity. The emergence of traffic (i.e., many interacting vehicles using a common infrastructure) and subsequently traffic congestion (whereby demand temporarily exceeds the infrastructure capacity) have opened new innovation needs in the transportation area. One of the key tools for influencing the efficiency of traffic flow is traffic signal control that enables conflicting traffic to flow through intersections via the timing of green/red light cycles.