Spillover is a relatively severe traffic congestion state, which mostly occurs between two intersections that are close to each other with heavy traffic flow. During spillover, traffic order is chaotic, and traffic accidents are highly likely to occur alongside congestion. At least 2 to 3 police officers are required to maintain traffic order at spillover intersections. When there are too many spillover intersections in an urban area during morning and evening rush hours, it will impose significant pressure on police resource allocation.

As a special form of actuated control, spillover control involves installing detectors at road exits to identify the traffic flow spillover status of key road sections in real time and establish effective traffic spillover control strategies. This approach can free up police resources while improving traffic efficiency, ensuring traffic safety, and reducing accidents, making it an important component of traffic control.

To the north, the intersection in the case is connected to an urban expressway; to the south lies an auxiliary road with heavy traffic flow; and to the east and west are main roads. It serves as a key node for accessing the main urban area, as well as for the transition between the expressway and municipal roads.

During the morning rush hour at this intersection, there is high demand for vehicles exiting the expressway toward the main urban area, and spillover frequently occurs in the southbound direction. During the evening rush hour, there is significant demand for vehicles traveling northbound to enter the expressway and exit the main urban area, with frequent spillover in the northbound direction.

Since the northbound and southbound approaching traffic flows are both uncontrolled continuous flows, and the dissipation efficiency of northbound and southbound traffic fluctuates significantly due to expressway congestion, the spillover is random and difficult to predict. It is hard to improve this situation through fixed-cycle signal timing, and the impact of spillover is mainly reduced through remote manual intervention. When the congestion is severe during morning and evening rush hours, traffic police often maintain traffic order at the intersection.

To address the spillover issue at the case intersection during morning and evening rush hours, prevent traffic gridlock, and free up traffic police resources, MeritPlusData has designed a spillover detection and control algorithm based on the actual operation of the intersection. This algorithm can identify the traffic spillover status according to the geomagnetic spillover situation caused by traffic flow occupation and output spillover signals at different levels.

The spillover signals can be divided into three levels: slow-moving spillover, congested spillover, and severely congested spillover. Based on the spillover level corresponding to each direction, the traffic signal controller can be configured with the corresponding green light flow direction and the green light release ratio for that flow direction.

Layout Position of Spillover Detectors:
Two rows of spillover geomagnetic detectors are installed 68 meters away from the north exit, with a 4-meter interval between each row of detectors, which are used to detect the traffic spillover status of the north exit.
Two rows of spillover geomagnetic detectors are installed 63 meters away from the south exit, with a 4-meter interval between each row of detectors, which are used to detect the traffic spillover status of the south exit.

The spillover signals are received by the integrated radar-vision-magnetic detector and transmitted to the traffic signal controller.

During mild spillover, there will be multiple status indicators for activation and deactivation; during severe spillover, the activation status indicator will basically remain on. The difficulty of activating and deactivating spillover can be adjusted by modifying the time required to activate and deactivate spillover.

Assume that a slow-moving spillover occurs at the northbound exit. If the spillover flow direction is configured as the westbound motor vehicle left turn, with an operating time ratio of 70%, the corresponding 15th step of the variable phase sequence will be found based on the spillover flow direction (assuming the length of this step in the current configuration plan is 20 seconds). In this case, the green light duration for the westbound motor vehicle left turn at the 15th step will be 14 seconds, followed by a transition to flashing green, yellow light, and red light.

After the activation of spillover control, the traffic order at the case intersection is well-organized, and the traffic capacity has increased slightly. The transition from remote manual control to automatic spillover control not only ensures the traffic order at the intersection but also greatly frees up police resources.

The figure below shows the morning and evening rush hour traffic volume (vehicles passed per hour) on May 8th (when spillover control was activated) and May 18th (when spillover control was deactivated). The traffic volume increased slightly by 5.25% and 3.26% respectively.