Isolated Intersection
Requirements:
· Data: The turning movement count data collected in Part I and Part II will be used for this tutorial. You will be designing the signal plan for an intersection, depending on which intersection you have worked on for Part I and II.
· Software: Both Synchro and SimTraffic will be used in this tutorial. The software is available in the CE Computer lab
Data Preparation:
The turning movement count data and the geometry data of the intersection will be used. Suppose the intersection and data collected are shown in Figure 1.
Figure 1 Data collected for the designated intersection
Network Coding:
The first step for signal design in Synchro is to code the network. For this tutorial, since we will only perform the signal design for an isolated intersection, the network coding can be readily accomplished. Figure 2 below shows the interface of Synchro and indicates the button “Add Link” for adding links to the network. Click on this button and draw two segments on your screen. The first segment will be horizontal and the second one will be vertical.
*Note that you will have to reselect the “Add Link” button for each link.*
Figure 2 Illustration of adding links in Synchro
Next, double click on each link and edit its properties such as the length and speed limit, as shown in Figure 3. Input the road name, speed limit, and length for each link through this editing dialog. Once all the properties are edited click on Set Arterial Name and Speed. On the upper left, select the Show Speed and Show Link Length button to display the link speed and Length on the MAP view. *Note, this step is only to show you that all values are correct.
Figure 3 Illustration of editing link properties
You can also double click on the intersection and a dialog will appear for editing properties of the intersection, as shown in Figure 4. Try to change the location of this intersection to (3000, 4000) and leave other parameters untouched. Next, click on each node to change the X,Y coordinates. For example, on the ‘Node Setting’ dialog box for node 5 change it to X,Y=4000,4000. This means the distance will be 1000 ft away from the center of the intersection. If it isn’t within 30% of the link distance, you will have conflicts and will need to go back and edit your coordinates. We will use the pretimed signal design as an example, although in this tutorial you need to complete both the pretimed and actuated designs.
Figure 4 Illustration of node editing
Lane Group Design:
Keeping the intersection as “selected” (marked in a dark cycle), find and select the “Lane Settings” button from the toolbox of Synchro or simply pushing the “F3” function key, the lane design window will appear, as shown in Figure 5.
Figure 5 Illustration of lane design window
The lane Setting window is to input designated lane groups and related parameters. The arrows shown in the first row are selected via a pull down menu. The supporting data below them will be filled in automatically after you select the lane use arrows.
Notes: Synchro provides default values for most of the required parameters. In many cases, these default values work fine and you may not want to change them. Modify the default values only if needed.
Turning Movement Counts Input:
Click the button right next to the lane design one or simply pushing the “F4” function key. The volume Settings window will appear, as shown in Figure 6. Input the turning movement volume collected and the peak hour factor computed in Part I & II of this project. In our case, the volume data in Figure 1 will be input and we further assume the peak hour factor is 0.90.
Figure 6 Illustration of volume input
Leave all the other parameters in this window as is and input pedestrian and bicyclical volumes only if you have collected these data and they are significant for the intersection of interest.
Signal Design:
Push “F5” or click the button next to “Volume Settings” window, the signal design window (“Timing Settings”) will be displayed, as shown in Figure 7. Most of the parameters in this window can be set as the default ones. However, different options for “Turn Type”, “Protected Phase”, “Permitted Phase”, and “Lead/Lag” should be tested and their performances should be compared based on the resulting delays and level of service (LOS). Notice, however, the design for left turn has to follow certain criteria. Refer to the lecture notes for more detailed discussions. At the bottom of the window, the actual phasing plan will be provided graphically, according to the input data and chosen parameters.
Figure 7 Illustration of Timing Settings
Simulation in SimTraffic:
After the optimization of the signal design, click on “SimTraffic Animation” shown on the diagram below. You will then be able to see a simulation of the traffic regarding the intersection and its signal. Figure 8 demonstrates such a simulation. Notice if there is any queue in any approach of the intersection for your designed signal.
Figure 8 Simulation in SimTraffic
Interpret your Results and Draw Some Conclusions:
After finishing the design and optimization of the signal, you are now ready to answer the following questions. Write down your answers succinctly.
1. What are your optimized signal timing plans for both the pretimed and actuated designs? What parameters have you used in terms of “Turn Type”, “Protected Phase”, “Permitted Phase”, and “Lead/Lag” in the optimal plans?
2. What are the delays and LOS for each of the designs? Compare the delay measures with the data you collected.
3. Is there any queue on any approach when you simulate your designed signal timing plans in SimTraffic? If yes, how to further improve the signal design to reduce or eliminate the queue?