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Signal Control for Partial Cloverleaf Interchanges
Civil and Environmental Engineering
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This research was aimed at studying the signal operations at partial cloverleaf interchanges. Signal timing techniques on phase schemes, phase splits, and signal offsets were developed for two closely spaced intersections controlled by a single controller at partial cloverleaf interchanges. A case study was provided to demonstrate the feasibility of implementing a single controller at two closely spaced T-intersections that are commonly seen at a partial cloverleaf interchange. A discussion was made on the possible impacts of concurrent phase on cycle length with four-phase operation. The offset model developed in this research was designed for the unique traffic flow patterns at partial cloverleaf interchanges. The computational mechanism developed based on this model could be used to determine the optimum offset with considerations of delay and queue length between two intersections.Regression models for the estimation of interchange delay of partial cloverleaf interchanges were developed in this research. The delay equations used the sum of critical flow ratios to calculate the control delay at partial cloverleaf interchanges controlled by a single controller. These equations were constructed in the same format as the HCM models. Comparisons were made between diamond interchanges and different types of partial cloverleaf interchanges. Different interchange types were also compared in terms of lane imbalance. For the evaluation of partial cloverleaf interchanges, a comprehensive model was developed to provide an accurate estimation of additional lost time due to the presence of a downstream queue. When the distance between the upstream intersection and the downstream queue was short, the proposed model provided more accurate estimations compared with the models in the Highway Capacity Manual 2010.