The development of Taiwan arterial traffic-adaptive signal control system and its field test: a Taiwan experience

Journal of Advanced Transportation, Winter, 2009 by Yueh-Tzu Wu, Chi-Hong Ho

This Taiwan traffic-adaptive arterial signal control model borrowed its traffic flow framework mainly from a British traffic-adaptive control model with a cyclic traffic progression function, i.e. SCOOT (Split Cycle Office Optimisation Technique). The new arterial control model can take into account delays of both major and minor streets and make real-time signal timing decisions with optimal two-way signal offsets, so as to create the best arterial signal operation performance. It has been developed to be an online real-time software for both simulation testing and field validation. Through simulation, it was found that the performance when operating this newly developed real-time arterial traffic-adaptive model was significantly better than when using the optimal fixed-time arterial timing plan. On the aspect of field testing, three signalized intersections located in East District, Taiwan City, Taiwan were selected to be the test sites. Fairly good traffic control performance has been demonstrated in that it can effectively reduce travel delays of the control arterial as a whole. Additional discussions about how to combine travel delay and the total number of vehicle stops into a new control performance index have also been included to make the new traffic-adaptive model more flexible and reasonable to meet the expectations of different driver groups in the arterial system.

Keywords: Traffic-adaptive Signal Control, Coordinated Arterial Signal System, Simulation Study, Field Test.

1. Introduction

Modern traffic signal control systems, especially those based on traffic-adaptive signal logic, have proven to be one of the most efficient measures to improve urban traffic congestion problems. In 1963, Miller presented a new algorithm to deal with signal optimization problems, and the traffic-adaptive signal control logic has been studied for more than 40 years since then. More than 10 traffic-adaptive signal control models have appeared as of now. These models can be divided into two categories. The whole cycle length for signal timing plans in the signal optimization process has to be decided for one category. The other applies the dynamic programming theory for determining each phase length.

Some of these control logics have been significantly enhanced with advanced functions, and new versions of them are continuously being developed. Therefore, these control logics possess greater capabilities to provide optimal signal plans for complex traffic situation. These capabilities have even been verified and validated in the real world. The multi-criteria traffic-adaptive control logic, implemented in Vancouver, Canada, for example, is an interesting case, which adopts some criteria of traffic flow to improve its traffic prediction model as well as optimal signal timing. [Lam and Craig, 2004]. The Real-time, Hierarchical, Optimized, Distributed, Effective System (RHODES) implemented in the San Francisco Bay Area also serves as an illustrative example for verifying the performance and experiences of a traffic-adaptive control system. [Aguigui and Hong, 2003]

In Taiwan, most big cities have similar traffic signal problems that often result from short block lengths. Two adjacent intersections are too close to each other, so the timing plan of one intersection has great influence on another one that is near by. A possible solution is to coordinate green times, thus the vehicles may pass through the set of signals efficiently.

Many academic reports for dealing with traffic signal problems by applying traffic-adaptive signal control have been published. The research group at the National Cheng Kung University has been studying traffic-adaptive signal control logics since 1989, and their most famous achievement on traffic-adaptive signal control logics is named COMDYCS-3 (Computerized Dynamic Traffic Control System 3), which is designed for application in isolated intersections. In simulation or field tests, the results from COMDYCS-3 have shown excellent performance.

This study aims to introduce two traffic-adaptive signal control logics. One expands the structures and functions of the previous traffic-adaptive signal control system, COMDYCS-3, so that it can handle more than one intersection during the same time period. The other adopts the concept of a cyclic point of view to improve the performance, focusing on total system delay and platoon progress of arterial streets. Both traffic-adaptive signal control logics use travel delay and stopped frequency in the performance index. These two traffic-adaptive signal control logics have been developed for real-time traffic control systems, and both adopt the distributed parallel process operation model to connect the data to each other.

Due to the limitations of time and research funding, three signalized intersections located in East District, Tainan City, Taiwan were selected to be the test arterial sites. The arterial sites should avoid alley entrances, bus stops and parking spaces. Besides, in order to reduce interference to the traffic progress, the traffic flow of motorcycles and the behavior of changing lanes were not taken into consideration.