One Way Coordination
For the first case study in coordinated signals you will be modeling a stretch of the US 95 couplet in Moscow, ID.
Your task for this case study is to first calculate the system cycle length and offsets by hand. After you have done that, construct the system in Synchro using your calculated times. View the results, taking note of delay times, LOS, and v/c ratios. Once you have done that, use Synchro to optimize the system and view the new results.
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 Permitted and use two phase cycles (one for Jackson and one for the cross street). Then calculate the green splits and the overall timing plan for each intersection.
Step 2: Find Offsets
Use the equation given on the One Way Coordination Background page. Assume that the A street intersection will be your master intersection (offset of zero). 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. 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 Jackson, 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. The controller instructions assume you have used NEMA phase 2 for the south bound traffic and phase 4 for the the east-west traffic.
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
Continue on to Case Study 10.