## 3 Signal Control Method
### Coordination of Main and Pre-Signal Control  
#### 3.2.1 Process of Coordination Control  
According to the proposed control method, the basic idea of the coordinated control of main and pre-signal in the integrated waiting area is shown in Figure 5. The arrived right-turn vehicles are not controlled by the pre-signal. Right-turn vehicles pass through the intersection according to the give way rules. The pre-signal is used to control the direction of the available lanes in the integrated waiting area. The available lanes serve through and left-turn traffic alternately in a signal cycle. Right-turn vehicles will use the rightmost lane in the integrated waiting area as shown in Figure 2.  
The rules of pre-signal control are as follows:  
1. The arrived right-turn vehicles are not controlled by the pre-signal. They will use the rightmost lane in the integrated waiting area. 2. The arrived through and left-turn vehicles should stop at the pre-stop line to wait for the corresponding green light of the pre-signal. When pre-signals at the approach provide a green indication for the through movement, all the through vehicles stopped at the pre-stop line are permitted to enter the integrated waiting area and distributed in all the available lanes in the integrated waiting area. The arrived left-turn vehicles should stop and wait in line at the pre-stop line. Vehicles that distributed in the integrated waiting area  
Figure 5: The coordination control strategy of the main-signal and pre-signal. (Note: Solid arrows indicate lane direction, dashed arrows represent vehicles trajectory). stop while the main signals provide a red indication for the through movement. When the main signal light of this phase turns green, all the vehicles waiting in the integrated area will start to pass through the main stop line into the intersection. Meanwhile, the other through movement vehicles that have not yet entered the waiting area may also go through the waiting area directly. Therefore, vehicles going through the intersection are cleared gradually. At the same time, the left-turn vehicles arriving will stop and wait at the pre-stop line. After some time, the pre-signal lights for through movement will turn red. Thus, the through movement vehicles will have to stop entering the waiting area. After the vehicles distributed in the integrated waiting area are cleared, the main signal light for the through movement turns red. Then the left-turn phase of the pre-signal turns green. Similarly, the left-turn vehicles waiting at the pre-stop line will start to enter the integrated waiting area and distribute in the available lanes. All the lanes in the integrated waiting area will be utilized for the left-turn vehicles. The through movement vehicles arriving should stop and wait in line at the pre-stop line. All the left-turn vehicles are waiting in the integrated area while main signal lights for the left-turn movement keep red. When the main signal lights for left-turn turn green, all the vehicles waiting in the integrated area will start to pass through the main-stop line into the intersection. Meanwhile, the other left-turn vehicles that have not yet entered the waiting area may also pass directly through the waiting area. Thus, left-turn vehicles will also be cleared gradually. After some time, the pre-signal lights for left-turn vehicles will turn red. Thus, the left-turn vehicles will have to stop entering the waiting area. When all the left-turn vehicles distributed in the integrated waiting area are cleared off, the main signal light for left-turn vehicles turns red. The operation of the integrated waiting area will switch to the through phase and follow this cycle back and forth. More importantly, clearance of the vehicles in the waiting area is critical, as it directly affects the normal traffic of the other directions in the waiting area afterwards.