T3 Webinar Presentation

Virtual Intersections: Using Simulated Traffic Signals in Mobile Signal Timing (MOST) Training (April 15, 2009)

Demonstration of Experiments Relating to Isolated Intersections (Labs 2 through 5)

Presenter:   Michael Kyte
Presenter's Org:   University of Idaho

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Slide 1:  Demonstration of Experiments Relating to Isolated Intersections (Labs 2 through 5)

Michael Kyte
University of Idaho
15 April 2009

Slide 2:  Parts of the Presentation

Laboratory 2. Effect of detector and timing Parameters on the Operation of the Cross Street of an isolated intersection.

Laboratory 3. Developing Timing Plans for Efficient Intersection Operations During Moderate Traffic Volume Conditions.

Laboratory 4. Impact of Detector and Timing Parameters on Arterial Street Operations at an Isolated Intersection.

Laboratory 5. Selecting Left Turn Phasing for Various Traffic Volume Decisions

Slide 3:  Structure of Laboratory

Introduction

Terms

Experiments

Closure: Summary of Key Points Learned

Slide 4:  Structure of Laboratory — Section 1

1.1 Purpose

How and when should a green indication terminate at a signalized intersection? There are a number of factors that affect the termination of green including the desired efficiency of traffic signal operation, the quality of service provided to motorists, and the safety of motorists traveling through the intersection.

1.2 Goals and Learning Objectives

The goal of Laboratory 2 is to develop a detector design (length of the detection zone) and timing design (Minimum Green and Vehicle Extension time parameters) for a cross street at an isolated intersection.

1.3 Organization and Time Allocation

Laboratory 2 is divided into nine sections, including this introduction. The eight sections that follow and the approximate time allocated to each section are listed in Table 1.

[A table appears with columns for Section, Title, and Approximate Time (min)].

Slide 5:  Structure of Laboratory — Section 2

2. Terms

Standard definitions for traffic signal terminology are provided by the National Electrical Manufacturers Association (NEMA) [9] and by the National Transportation Communications for ITS Protocol (NTCIP) 1202 document, "Object Definitions for Actuated Traffic Signal Controller Units" [2]. Definitions are also provided in the Federal Highway Administration's Traffic Signal Timing Manual [5]. The definitions provided here are adapted from these sources.

Actuated Time Signal Control: A type of signal control in which the timing of each phase is at least partially controlled by detector actuations.

Actuation: The operation of any type of detector.

Call: An actuation of a phase by vehicle detection or by an internal signal controller setting (a "recall"). A phase that is not called will be skipped.

Gap Out: A method of terminating a phases resulting when the Passage Timer expires.

Slide 6:  Structure of Laboratory — Section 3

3. Experiment #1: How a Traffic Phase Times

3.1 Learning Objective

3.2 Overview

The purpose of this experiment is to observe the timing of a traffic phase and the method by which the phase terminates. You will observe the SB approach (phase 4) of the intersection of State Highway 8 and Line Street. This approach (Line Street) has two lanes, a left turn lane and a through/right turn lane. State Highway 8 is the major street and serves as a primary east-west route through the city. It also serves as the major access to a university . See Figure 1. You will monitor traffic on the through/right turn lane of this approach.

3.3 Questions to Consider

As you begin this experiment, consider the following questions. You will come back to these questions once you have completed the experiment.

Slide 7:  Structure of Laboratory — Section 9

9. Closure: Summary of Key Points Learned

In this laboratory you looked at the factors that should be considered when the Minimum Green time and the Vehicle Extension time parameters are set, for a given length of the detection zone. It should be pointed out that we've only considered stop bar detection, and other detection zone configurations will result in different results.

You saw in Experiment #1 how a phase times and two common ways in which a phase is terminated: (1) The Minimum Green and Vehicle Extension timers both expire, resulting in a "gap out", and (2) the Maximum Green timer expires, resulting in a "max out".

You saw in Experiment #2 that the detection zone itself can provide some extension of the green as vehicles arrive at the intersection and enter the zone. A longer zone provides more of this extension capability.

Slide 8:  Structure of Laboratory

Slide 9:  Structure of Experiments — Section 3

3.1 Learning Objective

3.2 Overview

The purpose of this experiment is to observe the timing of a traffic phase and the method by which the phase terminates. You will observe the SB approach (phase 4) of the intersection of State Highway 8 and Line Street. This approach (Line Street) has two lanes, a left turn lane and a through/right turn lane. State Highway 8 is the major street and serves as a primary east-west route through the city. It also serves as the major access to a university . See Figure 1. You will monitor traffic on the through/right turn lane of this approach.

3.3 Questions to Consider

As you begin this experiment, consider the following questions. You will come back to these questions once you have completed the experiment.

3.2 Overview

The purpose of this experiment is to observe the timing of a traffic phase and the method by which the phase terminates. You will observe the SB approach (phase 4) of the intersection of State Highway 8 and Line street.

Slide 10:  Structure of Experiments

3.4 List of Steps

You will follow these steps during the experiment:

Slide 11:  Structure of Experiments — Section 3

3.5 Running the Experiments

In this experiment, you will consider two cases, each illustrating a different method for the termination of phase 4 (which serves the SB through/right turn movements.) You will observe how the phase times (the timing processes for the Minimum Green, Vehicle Extension, and Maximum Green timers), and how it terminates for each case. The two cases have been placed side-by-side in a movie format so that you can observe the traffic flow and timing processes at the same time. The simulation has been set to run at less than real time, slow enough so that you can observe all timing and traffic flow processes.

Step 1. Open the movie file.

Step 2. Observe the status at the beginning of phase 4 green.

Slide 12:  Structure of Experiments — Section 3

3.6 Discussion

Let's now consider each of the five questions that were presented at the beginning of this experiment.

Take a few minutes to review each question and write brief answers to each question in the box on the right based on your observations from this experiment.

Slide 13:  Demonstration: Laboratory 2, Experiment #1

Learning objectives

Overview

List of steps

You will follow these steps during this experiment:

Questions to consider

Slide 14:  Demonstration: Laboratory 2, Experiment #1

[This is the first page of a movie file of an example of actual traffic. This picture is a demonstration of the MOST laboratory #2 and experiment #1.]

Slide 15:  Demonstration: Laboratory 2, Experiment #1

  1. Why does the phase terminate for each of the two cases that you observed?
    In the first case, the phase terminated because the Vehicle Extension timer expired ("gapped out"). In the second case, the phase terminated because the Maximum Green timer expired ("maxed out").
  2. What is the process followed by the Minimum Green timer from the beginning of the green indication, until the timer expires? The Minimum Green timer begins timing at the start of the green indication. Its initial value is equal to the Minimum Green time. It continues timing until it reaches zero. The duration of the green indication is at least equal to the length of the Minimum Green time. See Figure 3.
  3. What is the process followed by the Vehicle Extension timer from the beginning of the green indication, until the timer expires?
    The Vehicle Extension timer begins timing when the detection zone becomes unoccupied and there is no call on the active phase. If it reaches zero, the green indication may terminate. If it has not expired, the Vehicle Extension timer is reset when another call is received. See Figure 4.

[This a XY graph that demonstrates how time increases the vehicle extension timer decreases.]

Slide 16:  Demonstration: Laboratory 2, Experiment #1

5. What are the two conditions that separately cause the termination of the green indication?

There are two conditions for termination of the green indication at an isolated actuated intersection: (1) the Minimum Green timer equals zero and the Vehicle Extension timer equals zero, or (2) the Maximum Green timer equals zero.

Figure 6 shows the ASC/3 controller status at t = 52.6, when phase 4 has just gapped out and the yellow interval has begun. This is the case on the left that you just observed.

Figure 6 shows the ASC/3 controller status at t = 71.4, when phase 4 has just maxed out and the yellow interval has begun. This is the case on the right side of the movie.

[There are screenshots of two status screens of the ASC/3 controllers from two separate simulations.]

Slide 17:  Demonstration: Laboratory 2, Experiment 6

8. Experiment #6: Design exercise-setting the minimum green time and the vehicle extension time.

8.1 Learning Objective

8.2 Overview

In the previous experiments, you learned about the effect of detection zone length on the duration of the green indication, the effect of the Minimum Green time in ensuring that a queue has sufficient time to begin to move at the beginning of the green indication, and the importance of the Vehicle Extension time in ensuring that the green indication extends long enough to serve a queue but not any longer.

In this experiment, you will set the Minimum Green time and the Vehicle Extension time for traffic conditions that you might find in the real world. This experiment includes four separate green intervals for the SB approach, with a mix of passenger cars and heavy vehicles, and a range of driver behavior characteristics. As before, the detection zone length is 22 feet. As a starting point, the Minimum Green time is set to 10 seconds and the Vehicle Extension time is set to 5 seconds.

8.3 Questions to consider

As you begin this experiment, consider the following questions. You will come back to these questions once you have completed the experiment.

8.4 List of Steps

You will follow these steps during this experiment:

Slide 18:  Demonstration: Laboratory 2, Experiment 6

Criteria:

[These are four pictures of traffic simulators demonstrating laboratory #2 and experiment #6.]

Slide 19:  Demonstration: Laboratory 2, Experiment 6

[This is the first page of a movie file of a traffic simulator demonstrating laboratory #2 and experiment #6.]

Slide 20:  Contact information:

Michael Kyte
University of Idaho
mkyte@uidaho.edu
208.885.6002

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