Home > Basic Signals > Exploration > Case Study 4

Case Study 1

Case Study 2

Case Study 3

Case Study 5

Case Study 6

# PLEASE - Read the Overlap Background page before continuing on. It will make things easier and less frustrating!

The object of this case is to find the optimal cycle length for the intersection of Case Study 3 using overlapped phases. How do the operations differ from Case Study 3?

 Movement NBLT NBTH NBRT SBLT SBTH SBRT Volume 360 868 66 231 748 50
 Movement EBLT EBTH EBRT WBLT WBTH WBRT Volume 96 146 80 105 133 98
 Desired v/c Ratio ((v/c)c) 0.85 Headway (h) 2 sec Peak Hour Factor 0.90 Lost Time per phase (tl) 3 sec Pedestrian Volumes 200 per hour Heavy Vehicles 8%

# Worksheet:

For this case study, we have an Excel worksheet which you may use or print out. If you decide to use Excel, be sure to right-click the link and "save target as" or "save link as."  If you are asked for a password, just press escape.

# Step 1: Phasing Plan

Normally you would check to see if left turns are warranted, but that was already done in Case Study 3. Since we are using overlapped phases, our phase diagram will look like this:

Conversion of all volumes to tcus. The equivalent factors may be found here. Remember that ELT for protected left turns is 1.05.

# Step 5: Green Split

Check your green split values for Phase A1, Phase A1+2, Phase A2+3, Phase A3, Phase B.

# Step 6: Signal Timing Plan

Signal Timing Plan includes the phasing plan, cycle length, and green splits.

# Step 7: NEMA Phasing

In order to input the timing plan into the controller, you must assign NEMA phase numbers to the phases (convert Phase A to NEMA Phase #, and so on). The link above should help with this.

# Step 8: Controller Settings

Follow all of the instructions given, especially the CLEAR and RESTART to ensure that your settings are properly implemented. Use the default all-red and yellow values (2 and 3 respectively).

When setting the lead/lag section in the controller, the phases in Ring 1 will need to be reversed. Also, it will be best to start both rings from Phase B from INIT (follow the controller settings link).

# Step 10: Traffic Simulation

Use TSIS to open "NIATT Signal Timing Project - Case Study 4 - Simulation.trf"

# Step 11: 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 three minutes.

# Questions

What do you notice about the simulation?

Does this seem to work better than the timing plan in Case Study 3?

Continue on to Case Study 5.