Area-Type Adjustment Factors for Non-CBD Signalised Intersections
American Journal of Civil Engineering
Volume 5, Issue 2, March 2017, Pages: 119-123
Received: Oct. 28, 2016; Accepted: Jan. 4, 2017; Published: Mar. 4, 2017
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Abena Agyeiwaa Obiri-Yeboah, Department of Civil Engineering, Kumasi Polytechnic, Kumasi, Ghana
Yaw Adubofour Tuffour, Department of Civil Engineering, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana
Mohammed Salifu, Department of Civil Engineering, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana
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In the estimation of saturation flow at signalized intersections using the HCM model, the influence of area-type characteristics on flow is accounted for by the area-type adjustment factor (fa). The recommendation by the manual to use fa=0.9 for CBD-intersections and 1.0 for all others tacitly assumes that the nature of non-CBD areas does not influence flow. This may not hold for many developing country cities and metropolitan areas where the roadside environments associated with non-CBD intersections may be laden with a flurry of activities that impact traffic flow. For signalized intersections in such areas, the HCM-recommended area-type adjustment factor could lead to over-estimation of saturation flow rates if the activities create substantial roadside friction to flow. This study set out to develop area-type adjustment factors for non-CBD signalized intersections located within the Kumasi Metropolis in Ghana, to accurately reflect the impact of roadside character on saturation flow rates. Using field saturation flow data collected at selected signalized intersections in the metropolis, area-type adjustment factors were developed for three distinct roadside friction environments categorised in the study as low/none, medium, and high. Average fa values developed were 0.99 for low/none, 0.98 for medium, and 0.94 for high roadside friction environments. Also, a multiple linear regression model that attempts to relate fa to pedestrian traffic interfering with flow within the environment of the intersection was developed as an alternative procedure for determining site specific area-type adjustment factor. It is recommended to use the fa values developed in this study in the HCM saturation flow model in order to estimate more accurately the saturation flow rates at non-CBD signalized intersections within the Kumasi Metropolis.
Area-Type Adjustment Factor, Non-CBD Signalised Intersections, Saturation Flow, Roadside Friction
To cite this article
Abena Agyeiwaa Obiri-Yeboah, Yaw Adubofour Tuffour, Mohammed Salifu, Area-Type Adjustment Factors for Non-CBD Signalised Intersections, American Journal of Civil Engineering. Vol. 5, No. 2, 2017, pp. 119-123. doi: 10.11648/j.ajce.20170502.17
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