Arterial Management Program

Model Systems Engineering Documents for Adaptive Signal Control Technology (ASCT) Systems

B. OVERVIEW OF THE PROCESS

Many engineers would like to first answer the question, "Is adaptive control right for my situation?" before proceeding with any analysis. However, there are so many situations in which adaptive operation may be better than the existing operation, and such a range of capabilities among the available adaptive systems, that it is almost impossible to answer this question without first developing a clear concept of operation. Only then can you decide whether you should proceed to develop adaptive system requirements. Look at the questions and statements in Figure 2. If one or more of these statements or questions applies to you, then adaptive control may be able to help you, and you should proceed.

Figure 2. Should You Consider Adaptive Control?
Diagram identifies questions that may be asked to determine if a user should consider ASCT.

One statement not in Figure 2 is the following: "Our agency desires to eliminate our traffic engineering staff by implementing adaptive control." Adaptive control is often marketed as eliminating the need for signal timing activities, but this is misleading. Observation of adaptive control projects indicates that ASCT improves performance, particularly when resources are limited, but that it still requires expert monitoring and adjustment over time. Even if this expertise is provided by a contractor or vendor, it will be required. Thus, if an agency lacks the resources to operate and maintain a traditional system, then ASCT probably should not be considered until those resources can be provided in a sustainable way.

Having decided to proceed, this process will guide you through the steps that are necessary in order to develop concise and relevant systems engineering documents for your project or situation. It does not do the engineering for you, that is up to you. Nor does it cover in detail the procurement, installation and operation of the system. The majority of the guidance covers the many decisions you will need to make in order to clearly define the system that you need. That process is illustrated in Figure 3.

Figure 3. Overview of Systems Engineering Flow Chart for ASCT System Definition
Diagram summarizes the many decisions that must be made to clearly define an adaptive system.

Templates for each system engineering document are included, as a quick reference guide for the structure of each document and the contents of each chapter. More detailed assistance is provided in the remainder of this guidance document.

In order to help you clearly define your needs in terms that will allow you to discriminate between the various adaptive systems that are available, and clearly define capabilities of your existing operation that must be retained with the use of adaptive operation, you will be guided through a series of questions. The answers to some of these questions will guide you to sample statements that may be included in the Concept of Operations. At each step, a description is provided of various situations that will lead you to different decisions. You should look for the statement that most closely describes your situation or aspirations. If you have a unique situation, you will be given guidance on how to describe it and how to frame suitable requirements that would address the situation.

After you go through these steps you will have a good idea of what you wish to achieve, and also the constraints within which you can then make a decision. Once you examine the constraints and decide whether or not any of the constraints can be removed, you will see whether any of the requirements are incompatible with the remaining constraints. This may lead you to reconsider the answers to some of the questions. This will be an iterative process until the remaining constraints are compatible with the functional requirements.

Following completion of the requirements, and before a system is acquired or developed, you will prepare a verification plan (to ensure the implemented system satisfies all requirements) and a validation plan (to ensure the operating system satisfies the needs defined in the Concept of Operation).

If the implementation of adaptive control would simply involve the design or selection of a new, stand-alone system that would replace any existing system and functions, the application of systems engineering principles would result in a linear sequence of events. This would involve defining your existing (As-Is) situation; needs, goals and objectives; your desired (To-Be) situation; followed by detailed requirements that will lead to selection and installation of a system.

However, since adaptive control will almost always be implemented in a location where there is an existing system, and the interface between an existing and a proposed adaptive system will be different for almost every combination of vendors and systems, a different approach is necessary in this case. The approach for developing your concept of operations passes through several of the steps multiple times, addressing one element at a time and gradually building up a complete picture of the concept and the high level requirements.

ASSEMBLING YOUR DOCUMENTS

The finished product of your efforts will be several systems engineering documents. In order to successfully prepare these documents, you will need to take the following steps.

  1. Read this document completely.
  2. Begin to prepare the Concept of Operations. Establish chapters in accordance with the Concept of Operations template. While you are free to format the document to suit your needs, the template follows the outline suggested in ANSI standard G-043-1992. As an alternative, you may simply take the table of sample statements and check those statements you wish to include.
  3. Following the instructions in this document, copy and edit relevant statements from the Table of Sample Statements for the Concept of Operations. Depending on how you answer each question in the guidance, select and edit each Concept of Operations statement.
  4. Some sections of the Concept of Operations require you to write appropriate text in accordance with the instructions contained in this document.
  5. Each statement in the Concept of Operations table has a unique identifier. The needs statements (Chapter 4) each refer to at least one relevant System Requirement that should be considered to support the need statement. Each Concept of Operations statement also contains a reference to the relevant section of this Guidance Document.
  6. Begin to prepare the System Requirements. Establish chapters in accordance with the System Requirements template. As an alternative, you may choose to include the System Requirements as an appendix to the Concept of Operations. In this case you may simply take the table of sample statements and check those statements you wish to include.
  7. For each need statement used from the Concept of Operations table, identify the System Requirements that are linked. Copy and edit each relevant requirement into the System Requirements document. Note that whenever you pick a "child" requirement, you should also select its "parent" requirement.
  8. If you describe needs in the Concept of Operations that are not covered by these sample statements, then you must also create related requirements.
  9. Prepare the Verification Plan. Establish chapters in accordance with the Verification Plan template. Note that every System Requirement requires a verification test, which you will need to prepare to suit your situation.
  10. Prepare the Validation Plan. Establish chapters in accordance with the Validation Plan template. Note that every need expressed in the Concept of Operations requires a corresponding validation test, which you will need to prepare to suit your situation.

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