Abstract
Traffic throughput at intersections can be improved by using exit lanes for left-turning (EFL), tidal flow lanes near an intersection, which has been recently introduced. This paper considers the operational robustness of the EFL intersection in relation to the control scheme applied to the traffic light setting. For safety and efficiency, it is important that the tidal lanes are emptied before traffic in the opposing direction uses these lanes. Hence, the signal control should not only be optimized for the mean value but be robust for all kinds of fluctuations. This paper formulates a traffic control scheme using robust optimization, i.e. an optimization scheme which explicitly accounts for extreme events. The fluctuation of traffic is considered from three aspects: the distribution of traffic demand, the distribution of base saturation flow rate, and the distribution of actual travel speed. Via a case study and extensive numerical analysis, we find that the established robust optimization method produces an efficient design of signal control and design speed at the EFL intersection under traffic demand and supply fluctuations. Though the optimization method is now applied to intersections with an EFL, it is considered useful for all intersections with high fluctuation of traffic demand and saturation flow rate.
Highlights
With rapid economic development and urbanization, roads in many cities have become increasingly congested
Its characteristic is that part of the exit lanes is set as a mixeduse area, which can be utilized as both exit lanes and leftturn lanes respectively at different stages of a signal cycle through the coordination control of main and pre-signal
There are some constraints on the layout design of the exit-lanes for left-turn (EFL) intersection, including that (1) the shared left-turn and through lane should be forbidden; (2) at least one normal approach lane should be assigned for the left-turn; (3) the total number of left lanes should not be greater than the number of exit lanes in the receiving leg [18]
Summary
OF EFL INTERSECTION The geometric structure of the EFL intersection is shown in Fig. 1 [18], where the yellow zone is the mixed-use area. The mixed-use area can be used as exit lanes or left-turn lanes, respectively, during different stages of a signal cycle. When the left-turn green light at the main signal is turned on, both vehicles in the mixed-use area and conventional leftturn vehicles can turn left at the same time to pass through the intersection. The clearance time needs to be long enough to guarantee the smooth emptying of vehicles in the mixeduse area It means the green light at the pre-signal shall be turned on after the end time of previous conflict phase and turned off before the end of left-turn green light at the main signal. We will propose a signal timing model for EFL intersections with the consideration of traffic. Fluctuations from the following three aspects: (1) the distribution of traffic demand, (2) the distribution of base saturation flow rate, (3) the distribution of the actual travel speed
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