laboratory 2 – experiment #1 how a traffic phase times 15 – … · 2009. 7. 6. · instructor...

MOST (Isolated Intersections) Instructor Guide

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Laboratory 2 – Experiment #1 How a Traffic Phase Times

15 – Minutes


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Instructor Preview

Relationship of This Experiment to MOST Course This experiment is the first of six experiments in Laboratory 2 of the MOST course. The relationship of this laboratory to the others in the MOST course is shown in Figure 1.

Figure 1 MOST Laboratories and Goals


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Figure 2 shows the seven MOST laboratories and the experiments that are included in each laboratory.

Figure 2 MOST laboratories and experiments

MOST

Tools

Isolated intersections

Coordinated systems

1. Introduction to simulation tools

2. Effect of detector and timing parameters on the operation of the cross street of an isolated intersection

3. Developing timing plans for efficient intersection operations during moderate traffic volume conditions

4. Impact of detector and timing parameters on arterial street operations at an isolated intersection

5. Selecting left turn phasing for various traffic volume conditions

6. Actuated traffic signal coordination concepts

7. Programming a system of actuated coordinated signals

Laboratories Experiments

#1: Simulation and the real world#2: Using the MOST interface#3: Exploring VISSIM#4: Navigating the ASC/3 controller

#1: How a traffic phase times#2: Effect of detection zone length on green duration#3: Determining the length of the Minimum Green time#4: Observing vehicle headways in the departing queue#5: Relating headway to unoccupancy time and Vehicle Extension time#6: Design exercise- setting the Minimum Green time and the Vehicle Extension time

#1: Determining the effect of minor street Vehicle Extension time on intersection operations#2: Determining pedestrian timing parameters #3: Determining the effect of Maximum Green time on intersection operations#4: Design exercise- setting timing parameters for both approaches of an intersection

#1: Minimum Green setting for advance detection serving the initial queue when advance detection is used: two possible solutions#2: Variable Initial setting for volume-density control#3: Vehicle Extension setting for advance detection volume-density gap reduction process: how it works#4: How gap reduction process works#5: Gap reduction process for volume-density control#6: Design exercise- setting volume-density parameters

#1: Permitted left turn operations#2: Comparing permitted and protected left turn phasing#3: Comparing protected/permitted and protected left turn phasing#4: Design exercise- determining appropriate left turn treatment

#1: Becoming familiar with coordinator status screens #2: Detector mapping and pitfalls#3: Extension time adjustments pitfalls#4: Adjusting splits on minor lefts#5: Balancing split times across barriers #6: Reallocating slack green time#7: Changing cycle length and observing impacts#8: Offset adjustment#9: Leading and lagging left turns with coordinator#10: Estimating volume to capacity ratios#11: Integrating Synchro outputs into VISSIM ASC/ 3 database

#1: Programming controller parameters for coordination#2: Design exercise-improving coordinated operation


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What the Students Will Do and Observe The learning objective for this experiment is:

“To be able to describe the primary methods for the termination of a traffic phase at a signalized intersection”

To accomplish this objective, the students will observe a movie file that shows two intersections, side-by-side, each showing a different method of phase termination. They will record their observations during and after watching the movie file, and then answer questions that relate what they observed to the learning objective. The movie file is 3:24 in length; they will observe the first 2:54. Figure 3 shows what the students will see at the beginning of green for the window on the left. Make sure that you point out (in the slides that follow), the simulation time, the active phase (“T”), the detector status (active call noted by “C”), and the active timing processes (shown here are the MGRN and MAX1 timers).

Figure 3 Movie file


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Figure 4 shows three segments of the movie file: (1) the set up, (2) the left window showing the phase terminating as a result of a gap out, and (3) the right window showing the phase terminating as a result of a max out. For each time segment, the chart shows the initial status of the subject approach with respect to the traffic, the display, the detector, and the controller. The same information is shown for the events that transpire during the segment itself. Study this information carefully so that you know what the students will observe as they watch the movie file. One of their major tasks is to learn to relate traffic flow and the control processes.

Figure 4 Segments of the movie file

Left windowSet-up Right window

Subject approachLeft windowSB, phase 4

Traffic status(left window): 1 vehicle in queue; another about to join queue

Display statusRed

Detector statusCall (C) on phase 4

Controller statusActive phases (2 and 6) timing (T)

Traffic status(left window): Second vehicle joins the queue

Display statusRed


Controller statusPhases 2 and 6 yellow and all red timers time down and phases gap outPhase 4 is phase next (N)

Subject approachLeft windowSB, phase 4

Traffic status(left window): 2 vehicles in queue

Display statusRed


Controller statusActive phase (4) timing (T)MGRN = 5.0 secMAX1 = 0.0.sec

Traffic status(left window): Vehicle queue starts and clears

Display statusGreen

Detector statusCall (C) on phase 4 active until second vehicle leaves detection zoneCall on phase 2 at t = 46.2

Controller statusMAX1 begins timing when conflicting call received (t = 46.2)VEXT begins timing when vehicle 2 leaves zone (t = 50.2)MGRN expires (t = 50.6)VEXT expires at t = 52.6 and phase gaps out

Laboratory 2, Experiment 1: How a traffic phase timesLearning objective: Be able to describe the two primary methods for the termination of a traffic phase at an isolated intersection.

Subject approachRight windowSB, phase 4

Traffic status(right window): 9 vehicles in queue

Display statusRed

Detector status: Call (C) on phase 4

Controller statusActive phase (4) timing (T)MGRN = 5.0 secMAX1 = 20.0.sec

Traffic status(right window): Vehicle queue starts and moves continuously throughout green

Display statusGreen

Detector statusCall (C) on phase 4 active as vehicle queue moves through detection zoneCall is dropped temporarily between vehicles (when zone is empty)

Controller statusMAX1 begins timing at beginning of green because of active conflicting callMGRN timer expires at t = 56.4VEXT begins timing when call is not active (detection zone is empty), but never expires as unoccupancy time never exceeds 2.5 secMAX1 timer expires at t = 71.4 and phase maxes out


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Key Points to Remember • It is important that the student develop observational skills by

knowing what is important to look for in each movie file or animation. These are skills that a traffic engineer will need to use in the field: how is traffic flowing and what are the controller and detector settings that influence the quality of the traffic flow.

• For an isolated signalized intersection, a phase can terminate in two ways.

• A phase will gap out when the vehicle extension timer (VEXT) times down to zero, after the minimum green timer (MGRN) has timed down to zero. The vehicle extension timer begins to time when the call on the phase is inactive (dropped). The minimum green timer begins to time when the phase becomes active.

• A phase will max out when the maximum green timer (MAX1) times down to zero. The maximum green timer begins to time when a call on a conflicting phase is received.


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Key Message:

In this experiment you will learn about how a traffic phase times and methods by which a phase can terminate.

Background Information:

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Interactivity:

Tell: Turn to page 61 of your book. This page lists the learning objective for this experiment, an overview of the experiment, the questions that you will answer once you’ve finished the experiment, and the list of steps that you will complete during the experiment. Take about two minutes to read this page. [Once they have completed reading the page] Tell: Do you have any questions on this material?

Notes:


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Key Message:

There is a specific set of steps that they need to follow. All of the details are given on pages 62 and 63.


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Interactivity:

Tell: Turn to page 62 of your book. Read through the instructions before beginning the experiment. Once you have completed the reading, begin the experiment. When you have completed the experiment (through page 63), record your observations on the box provided on that page. Don’t start quite yet!

Notes:


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Key Message:

One of the most important aspects of the MOST course is to learn to observe traffic flow conditions, the status of the detectors and signal displays, and the status of the controller timing processes.


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Interactivity:

Tell: When you have opened the movie file, pause for a moment to look at the screen and see what you can observe. Note that there are always four kinds of information:

• The traffic flow conditions • The status of the detectors (active or off) • The status of the controller and the various timing

processes • The status of the signal display (red, yellow, green)

Ask: What do you see in this slide? Possible responses: (1) the phase that is timing, noted with a “T”, (2) the phases on which there are active vehicle calls, noted with a “C”, (3) the phases that are timing for each ring, and (4) the values of the currently active timing processes, here the


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minimum green timer and the maximum green timer. Notes:


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Key Message:

One of the most important skills to develop is to observe. What is important in a given animation or movie file? At the end of each experiment, the student is given the opportunity to reflect on the experiment and record their observations.


You can refer to the charts and text on pages xx to xx of the Instructor Guide for further details about what the students will be observing.

Interactivity:

Tell: OK. You can now complete Experiment #1. When you have completed step 3, write down your observations in the box on the right of page 63, as noted in step 4. Why do we record observations? One of the most important skills that we want you to develop in this course is to learn to observe and make judgments about how well (or not) traffic is flowing based on what you observe about the traffic flow, the detector status, the controller processes, and the signal display.

Notes:

Give the students about 5 minutes to complete their observations and make notes.


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Key Message:

One of the key elements in the learning process upon which the MOST course is based is the discussion. Students are given questions to consider at the beginning of each experiment. Once they complete an experiment, they are asked to review and answer each of these questions.


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Interactivity:

Tell: Turn to page 64 of your book. You are presented again with the “questions to consider.” Review these questions with you partner (if you are working with a partner) and write your answers in the box provided on the right of page 64. Be ready to discuss your answers with the class.

Notes: Take about 5 minutes for this activity.


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Key Message:

Discussion of their answers is a critical part of the learning process.


For an isolated signalized intersection, phases can terminate in two ways.

• A phase will gap out when the vehicle extension timer (VEXT) times down to zero, after the minimum green timer (MGRN) has timed down to zero. The vehicle extension timer begins to time when the call on the phase is inactive (dropped). The minimum green timer begins to time when the phase becomes active.

• A phase will max out when the maximum green timer (MAX1) times down to zero. The maximum green timer begins to time when a call on a conflicting phase is received.

Interactivity:

Ask: Why does the phase terminate for each of the two cases that you observed. [The answers are shown on page 65 of the book]

Notes:


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Key Message:

There are defined processes that are followed by the these three timers. Together with the vehicle calls, these timers determine how long a phase will time and when it will terminate.


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Interactivity:

Ask: What is the process followed by each of these three timing processes.

Notes:


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Key Message:

Encourage the students to study these charts.


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Interactivity:

Possible responses: The responses are given on page 65 of the book. Ask: Do you have any questions on these charts and the processes that they represent?

Notes:


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Key Message:

For an isolated intersection, there are two conditions for the termination of a phase. The first condition is the “gap out”. Here, both the minimum green timer and the vehicle extension timer must reach zero. The second condition is the “max out”. For this condition to occur, the maximum green timer must reach zero.


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Interactivity:

Ask: What are the two conditions that separately cause the termination of the green indication?

Notes:


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Key Message:

In this experiment you will learn about how a traffic phase times and methods by which a phase can terminate.


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Interactivity:

Ask: What are the conditions shown for each of the two examples displayed here? Possible responses: The figure on the left shows the gap out. There are has not been any active vehicle calls for a time duration equal to the value of the Vehicle Extension time. The figure on the right shows the max out. The maximum green timer has just expired, even though there is still an active call on phase 4.

Notes:


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Key Message:

This slide shows the actual values of the timing processes that you observed for the traffic in the left window.


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Interactivity:

Ask: What do these charts show? Answer: These charts show the actual values of the timing processes for the first condition that you observed, the gap out. The minimum green timer begins to time at the beginning of the phase and it continues to time down until it reaches zero, 5 seconds later. The vehicle extension timer becomes active when the detection zone is empty (no active calls). Since no other vehicles arrive at the intersection, the timer continues until it reaches zero, 2.5 seconds after it started to time.

Notes:


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Key Message:

This slide shows the actual values of the timing processes that you observed for the traffic in the right window.


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Interactivity:

Ask: What do these charts show? Answer: These charts show the actual values of the timing processes for the second condition that you observed, the max out. The minimum green timer begins to time at the beginning of the phase and it continues to time down until it reach zero, five seconds later. The vehicle extension timer begins to time when the detection zone is empty. Here, it is reset to its original value (2.5 seconds) eight times, as the queue continues to move through the intersection. The maximum green timer begins to time when there is a call on the conflicting phase and times to zero.

Notes:


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Key Message:

We will always come back to the learning objective, the basis for each experiment.


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Interactivity:

Ask: Do you think that this learning objective has been met? Do you still have any questions about the methods by which a phase can terminate? Tell: We are now ready to move to Experiment #2, in which you will continue to build on this knowledge of how a phase times (and terminates).

Notes:

laboratory 2 – experiment #1 how a traffic phase times 15 – … · 2009. 7. 6. · instructor...

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