Efficient traffic signal operation is greatly beneficial to road users. Due to the intensive labor required, even though traffic signal retiming has a very high benefit/cost ratio, most of the traffic signals in the US are retimed once every 3-5 years or longer. Such practice may miss the opportunities for operational improvements and lead to unnecessary delays. One of the major obstacles is the limited capability of data collection and a lack of convenient performance monitoring tools for signalized arterials. To make up for this limitation, this paper proposed a performance diagnosis tool for arterial traffic signal system. The tool aims at identifying necessary parameter changes and assisting agency to automatically fine tune the traffic signal system. A flexible and low cost data collection unit (DCU) is developed for the tool to enhance traffic signal cabinets with event-based data collection capability. Three major parameters of traffic signals, offset, green split and cycle length, are then evaluated in the data center via diagnosis modules utilizing event-based traffic data. The development of DCU as well as the diagnosis methodologies is described in details in this paper. The implementation of the tool is illustrated by field data analysis at intersections on Minnesota Trunk Highway (TH) 13 in Savage, MN.
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