Effective and Robust Coordination of Traffic Signals on Arterial Streets, Volume 1, Research Report

Abstract

Many transportation agencies use Synchro and SimTraffic software package to optimize signal coordination. In general, this software package effectively reduces the efforts of traffic systems engineers and improves the quality of the designed coordination. Nevertheless, the initial solutions given by the software packages usually require adjustment, at both the design and implementation stages. The major objective of this research, therefore, is to reduce the time and effort needed in solution tuning and thus to improve the effectiveness and the efficiency of using Synchro/SimTraffic in arterial signal coordination design. The research outcome is expected to help traffic systems engineers reach reasonable signal settings in a shorter time. The first task of this research was to survey INDOT traffic system engineers and document INDOT’s criteria for a good coordination plan. The outcome of this task served as the yardstick for other proposed design improvement procedures. The second part of the research focused on the Synchro/SimTraffic-based procedures of optimizing signal settings for urban streets and the practices and methods of using Synchro were scrutinized thoroughly. The outcome of this part of the research is a collection of supplemental guidelines for software-based selection of signal settings on urban streets. Finally, the robustness of the arterial signal coordination procedure was investigated. In current practice, signals are optimized to traffic volumes that represent a single time interval. In spite of the randomness of traffic, these plans, however, are executed for a long period of time until obvious insufficiencies of the signal timings are noticed and re-timing is necessary. The robustness of several alternative approaches was considered in the same traffic condition settings. The outcomes of these investigations are assembled into the second volume of this report, Guidelines of Design. The guidelines are in accordance with the defined criteria of good signal control along urban streets. The guidelines are not a manual of arterial signal design since every arterial system has its individual problems and requires specific treatment that cannot be reached by a uniform set of procedures. Instead, experiences collected from current traffic systems engineers and lessons learned through research are compiled into the guidelines to help reduce field tuning of the signal settings. The resulting guidelines are practical and they require no extra data beyond the current data collection practice. The guideline can serve as a reference for experienced traffic engineers and as an educational tool for new traffic engineers. The robustness of the signal design procedures was also investigated. Models for extracting the traffic variation pattern from 12 hours of traffic counts were developed based on real data collected at Purdue University. These models were used to generate reasonable traffic inputs to the micro-simulation tool. The robustness of the current signal design procedures was evaluated using these simulated traffic inputs. Several practical alternatives to the current arterial signal optimization were also evaluated using the same inputs. The performances of these methods were compared, and it was concluded that no obvious way to consistently improve the robustness of current signal design procedure is available.