CE 572 - Intersection Traffic Operations
Spring 2007

Web site of the day
McCain Traffic Control
Controller Interface Device

Objectives for today:

• Understand traffic controller subsystem

Topics:

• Traffic controller overview-the physical architecture
• Signal controller logic structure
• Terms/definition
• State transition logic
• Priority request service concepts
• Rings/barriers/phases
• Research problem assignments and requirements

Assignment:
In preparation for class 18, please complete the following reading assignment:

• Design Guidelines for Deploying Closed Loop Systems, section 2.2 (timing parameters), pp 11-20.
• Traffic Signal State Transition Logic Using Enhanced Sensor Information, pp 15-23.
• NTCIP 1202, pp 3-7 and pp 8-20.

Please be ready to discuss the following study questions:

1. What is a phase?
2. What is the minimum green time?
3. What are the clearance intervals?
4. What is the maximum green time?
5. What is the vehicle extension or passage time?
6. What factors in stop bar location affect the duration of the passage time?
7. What are the components of volume/density control and how do they operate?
8. What is dilemma zone protection?

And, based on the information presented on the timing elements defined in section 2.2.2 of NTCIP 1202, construct a phase table, or a table showing the data that are needed to define the timing elements for each phase.  This is just a matrix with the phase numbers across the top and the timing elements on the left side of the matrix. We will discuss the phase table at our next class.

Research problem assignments (Assignment 10)
The purpose of this project is to provide you with the opportunity to learn in more depth about a topic in signal timing and operations.

Requirements
1. Submit a bibliography or reference list, using correct citation format (see pp 9-10 of Transportation Research Board format), on relevant papers and reports by April 5th (Class 21).
2. Submit one page outline of paper by April 12 (Class 23).
3. Submit a chart that illustrates the process that your topic represents by April 12 (Class 23).
4. Submit the first draft of your paper by April 24 (Class 26).
5. Submit the final version of your paper by May 1 (Class 28).  The paper, with all elements, should be no longer than 10 to 15 pages.
6. Present the results of your research, using PowerPoint slides, on either May 1 (Class 28) or May 3 (Class 29).

Topic list (and team assignment)
1. Volume/density control: Amin, Ochoa, Sekulic
2. Determining passage time and minimum green length while considering detection zone length: Nayat, Taylor
3. Determining yellow and all red times, considering dilemma zone and option zone issues: Guo, Perez
4. Railroad preemption: Chipman, Madrigal
5.Transit signal priority: Rahman, Ekhator

Possible reference sources
1. NIATT library including all Transportation Research Records, NCHRP reports, and ITE Journals.
2. University of Idaho library.
3. Transportation Research Information Service online
4. National Cooperative Highway Research Program
5. Journal of Public Transportation
6. Midwest Transportation Knowledge Network
7. University of California, Berkeley, transportation library
8. References from NCHRP 3-66 interim report (pp 7-12 and 184-188)
4. Google searches

Class notes:
Written notes
Slides

Questions on today's class:
1. In video detection we can set the direction of movement to be detected to filter out the unwanted vehicle detections. Is there any settings for a loop detector for this?
Response: There is no way to do this with inductive loops.  But since most vehicles travel in their physical lane, this is not the problem that it is in video detection when the images of vehicles may cross over into the physical lane of an opposing movement.

2. Whenever there are intersections with approaches other than four, only in that case the standard phase diagram rules for rings may not be followed, right?
Response: The standard rings/barriers approach to describing the sequencing of phases may be used with any number of intersection approaches.  If there are fewer than four approaches, some of the phases may be omitted. 

3. There is a "conflict manager" unit inside the controller box. It was label "MMU" in the controller diagram. This manager prevents a situation where all phases are green. Is there a control that prevents all phases to be red?
Response: In fact, all phases are red during the "all red time", when the intersection is being cleared.  And, if all signals display red, while this may be a traffic flow problem, it is not a safety problem, which is the purpose of the MMU.

4. Does every intersection have to have its own traffic controller cabinet? Can one cabinet control more than one intersection?
Response: Each intersection must have its own traffic controller unit, and in most cases there is one cabinet located at each intersection.  Exceptions to this are at diamond interchanges at freeway off/on ramps and at single point urban intersections, where one controller can control two closely spaced intersections.

5. In class you mentioned that overlap occurs when two phases from different sides of the barrier run at the same time. So, can an overlap occur within a concurrency group? For example if phase 1 is running at the same time of phase 5 and then phase 5 ends and starts phase 6, but phase 1 continues, this is also an overlap?
Response: This is not an overlap since both phases are part of the concurrency group.  An overlap only occurs when a phase on the other side of the barrier is allowed to operate as a child phase to what would normally be a conflicting parent phase. For more on overlaps, see pages 9 and 10 of the report Design Guidelines for Deploying Closed Loop Systems.

6. On the exemption to phases operating across barriers, is it only possible at a t-intersection, or are there cases where overlapping phases can exist at a four approach intersection?
Response: An overlap can occur at an intersection of any size.  The example in class (a right turn operating with normally conflicting left turns) can be expanded to a four leg intersection.

7. Is the point that all things terminate on the precedence diagram the barrier, or is it something else?
Response: While some intervals (processes) can terminate at the barrier, some can also terminate at the end of a specific timing unit that occurs before the barrier. I'll have more examples when we discuss this in class.

8. In case of shadows from objects that cause light differences in the field of view like we observed on 6^th and Washington Streets (in which the shadows cover a big area), how can we solve this problem when using video detection?
Response: This is an important issue as shadows (either static or dynamic) occur in nearly all real world situations.  There are shadow algorithms that can be invoked in Autoscope along with sensitivity settings that help this problem greatly.  Nevertheless, you were exposed to a very extreme situation.