Two Way Coordination
For the second Case Study in coordinated signals you will be modeling a system based on a two way stretch of US 95 on the south end of Moscow, ID.
Your task for this case study will be to determine the best signal timing plan to use to coordinate the intersections of US 95 with the Troy Highway (S.H. 8), Sweet Ave., and Palouse River Drive. As in Case Study 9, you should try solving the system by hand first, modeling your solution in Synchro, then optimizing the system using Synchro. Take note of delay times, LOS, and v/c ratios.
The geometry and volumes are as follows (click on an intersection for geometry and volume information):
Assume all speeds are 30 mph (44 fps)
Hint: When modeling 3rd Street, just use two lanes for the westbound traffic.
Step 1: Signal Timing Plan
You will need to calculate the optimal cycle length for each intersection and use the longest one for all of the intersections (you can use a cycle length of half that value as well). Assume all left turns are at Palouse River Drive are Permitted, as is the left turn from NB 95 to Sweet Ave. Use two phase cycles at Palouse River Drive and Sweet Ave. In this Case Study, the phase numbering at US 95 and S.H. 8 is very important to getting the simulations to work properly. This is how we have numbered them. Once you have the cycle length you are going to use, determine the green splits for each intersection.
Step 2: Find Offsets
You can either use the equation given on the One Way Coordination Background page or the graphical trial and error method mentioned on the Optimization page. For this exercise, assume there is no internal queuing.
Step 3: Using Synchro
At this point you are ready to construct your simulation in Synchro. For the US 95/Troy Highway intersection, the right turns from SB 95 will be included in the south bound coordination. This will be important when you are numbering the phases. Follow the instructions in the module below to construct your model and view the outputs using:
- Your timing plans without offsets (uncoordinated)
- Your timing plan with offsets (coordinated)
- A signal timing plan optimized with Synchro
Using Synchro to optimize coordinated systems
Modeling Coordinated Signals in HILS
To go along with your work in determining the timing for the coordinated signals on US 95, we have developed instructions for programming traffic controllers for pretimed, coordinated operations. Using the controllers in conjunction with CIDs, you could model coordinated signals in HILS. The rest of this case study requires three controllers, three CIDs, and enough USB ports to connect them to your PC.
Step 4: Exporting your Synchro file to TSIS
This step is necessary because the CIDs are only configured to work with the TSIS simulation software.
With the file open in Synchro, go to the Transfer menu and select CORSIM Analysis. In the dialog box, change the simulation time to 60 minutes. Chose an easy to find location and save the file. Then, open TSIS and open the file you just created (use File - Open).
Step 5: Programming the controller
The instructions on this page must be followed precisely for this to work. We recommend that you get your controller network working properly before you experiment with different settings. Even though you timed your signals for two phase operation, you will need to load the controllers as if there is 4 phase, two ring operation at Sweet Ave. and Palouse River Dr. This is necessary because the US 95/Troy Highway intersection is a two ring intersection.
Step 6: Assigning intersections using the CID Configuration Tool
This is the same as with a single intersection, except you must do it for each intersection. Pay close attention that you assign the proper CID number to each intersection.
Step 7: Start the Simulation
Wait until all of the controllers have found their offsets before starting the simulation. On the Run Status screen, if the bottom left corner says "OFST" then it is ready. If it says "OFST SEEK" or "FREE" it is not ready.
Step 8: Execute Trafvu
This program allows you to view an animation of your signal. Do not start the animation until the simulation has reached equilibrium - usually about four minutes.
Step 9: Changing the Plan
Once the simulation is running you can change the controller to take on your timing plan or the timing plan calculated by Synchro. The instructions in step 5 set the controller to your timing plan, but with no offsets. To change the controller to have different splits and offsets, do the following:
- MM, 2, 3, 1
- PgDn and change SPL to 1 (your splits) or 2 (Synchro splits), and OFF to 1 (no offset), 2 (your offsets), or 3 (Synchro offsets).
- Press E.
It may take a cycle or two for the controller to fully implement these changes, and another few cycles for the changes to fully affect operations on the simulation.
Questions
After you have the network up and running, consider the following:
- How is coordination maintained between controllers? You know that you are using offsets, but how do the controllers know where the other controllers are at in their cycles? Or, do they even need to know?
- To what point in the cycle are the offsets referenced?
For each of the three trials you run, consider and comment on the following:
- Locations of poorly coordinated traffic
- Locations with excessive queuing
- Cross-streets with excessive delays and/or queuing
- Major street movements with excessive delays and/or queuing