  The semi-actuated coordinated operation mode is a type of signal control
where minor approaches are placed with detectors to develop actuated phasing
while major movements are coordinated without using detection systems. The
objective of this study is to propose a cost-effective approach for reducing
delay in the semi-actuated coordinated signal operation without incurring any
extra costs in terms of installing new detectors or developing adaptive
controller systems. We propose a simple approach for further enhancing a
pre-optimized timing plan. In this method, the green splits of non-coordinated
phases are multiplied by a factor greater than one. In the meantime, the amount
of green time added to the non-coordinated phases is subtracted from the
coordinated phases to keep the cycle length constant. Thus, if the traffic
demand on the side streets exceeds the expected traffic flow, the added time in
the non-coordinated phase enables the non-coordinated phases to accommodate the
additional traffic demand. A regression analysis is implemented so as to
identify the optimal value of the mentioned factor, called Actuated Factor
(ActF). The response variable is the average delay reduction (seconds/vehicle)
of the simulation runs under the proposed signal timing plan compared to the
simulation runs under the pre-optimized timing plan, obtained through the
macroscopic signal optimization tools. External traffic movements, left-turn
percentage, and ActF are the explanatory variables in the model. Results reveal
that the ActF is the only significant variable with the optimal value of 1.15
that is applicable for a wide range of traffic volumes.
