Measuring the benefits of adaptive traffic signal control: case study of Mill Plain Blvd. Vancouver, Washington

Ali Goudarz Eghtedari

ABSTRACT
The problem of controlling traffic signals?deciding when to allow vehicles to cross an intersection?dates back to the origin of vehicular transportation, and has been dealt with in various ways. The availability of detectors that transmit information on the real-time traffic status, and microprocessors that process this data, led to the development of adaptive, real-time traffic control systems. The superiority of adaptive traffic signal controls over the traditional approaches is now widely recognized. Literature suggests that on average a 15-20 % improvement in operation is expected when adaptive control systems replace older systems.

The City of Vancouver, Washington implemented an adaptive control system for traffic signal operations at 12 intersections along the Mill Plain Boulevard. Performance measurement of this system was the main objective of the research. Link, intersection, and travel-time data were compiled and statistically analyzed. Multivariate regression modeling, analysis of variance and other tests were used to compare performance of the system in the control case (time of day signal control) and the treatment case (adaptive signal control). In addition, data observed from travel-time runs (collected via a ?floating car?) and data collected from system detectors were used to develop several regression models to further examine the correlation between various measures of effectiveness (MOE) and the use of adaptive system and other independent variables.

This study aimed to answer the following questions:

• What performance-measure improvements can be achieved using a real-time adaptive signal control system on the subject corridor?
• Do side street users of the system enjoy the same level of improvement compared to users traveling on the main-line?

This research showed that adaptive traffic signal control generally has a positive impact on the system; however, differences could be observed based on the direction of traffic and volume thresholds. Eastbound traffic showed reductions of up to 20% in travel-time and 44% in total delay, with an almost 25% increase in average speed. Westbound traffic, however, was moderately impacted?negatively! A difference between side streets and main streets was measured, although the sample from the side streets was not large enough to draw strong conclusions.

April 29, 2005
DISSERTATION COMMITTEE
B. Kent Lall, Chairman
Robert L. Bertini
Franz N. Rad
Wayne W. Wakeland
Kenneth Dueker, Graduate Studies Rep.