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?
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
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.
- Read this document completely.
- 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.
- 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.
- Some sections of the Concept of Operations
require you to write appropriate text in
accordance with the instructions contained
in this document.
- 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.
- 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.
- 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.
- If you describe needs in the Concept of
Operations that are not covered by these
sample statements, then you must also create
related requirements.
- 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.
- 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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