Transcript Slide 1

Signal Group University
Traffic Controller Methodologies
NEMA-based vs. Interval-based
A lesson to attain a basic understanding of
the two traffic controller programming
methodologies used worldwide.
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SGU- NEMA vs. Interval
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NEMA
• NEMA stands for the National Electrical Manufacturers
Association. It is a volunteer organization of
manufacturers. It is NOT a government body. Section 3
of NEMA is designated as Traffic Systems, otherwise
known as NEMA 3-TS.
• Before 1989, there were no significant national traffic
controller standards. NEMA published TS-1 (1989) that
described a standard traffic controller for the general US
market. Multiple revisions of TS-1 and subsequently TS2 have been released and maintained by NEMA over the
past 20 years.
• NEMA TS standards are voluntary and are not required
that agencies use them in their own specifications.
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NEMA-based
• A NEMA-based traffic controller meets certain hardware
requirements, but also uses certain methodology and
terminology common to the NEMA TS standards.
• NEMA is often referred to as “phase based”, but this is
not an entirely accurate way to look at it because all
controllers use phases, not just NEMA controllers.
– Note: The term “phase” is universally used as interchangeable
with “vehicle movements”. (ex. A northbound through phase, or a
eastbound left-turn phase).
• A better description of NEMA is that it is phase “focused”.
This is because the timings for a particular phase can be
programmed independently for that phase and not
dictated by some other grouping in which that phase
belongs. (see next slide for further explanation)
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NEMA phase “focused”
• The green portion of NEMA phases are typically defined with a
minimum time and a maximum time that can be extended up to the
maximum in incremental “steps”.
• The amber portion is a fixed length parameter.
• If a phase is not green or amber, it is considered off (i.e. Red).
Minimum Green Time
Possible Green Extension
Step Time
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Amber
Time
Maximum Green Time
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NEMA phase “focused”
• Each phase can be variable based on the parameters set
for each individual phase.
Φ1
Φ2
Φ3
Φ4
Φ5
Φ6
Φ7
Φ8
Cycle Length
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NEMA Sequencing
• NEMA controllers use a ring
structure to determine the
sequence in which phases are
activated, or “served”. It also
uses this structure to determine
compatibility between phases.
– Compatibility simply means which
phases can be on (green or
amber) at the same time without
causing an unsafe traffic situation.
– NEMA allows multiple
simultaneous rings. Think of them
as stacked donuts.
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Φ1
Φ2
Φ4
Φ3
Φ1
Φ5
Φ4
Φ8
Φ2
Φ6
Φ3
Φ7
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NEMA Compatibility
Common NEMA 8-Phase, 2 Ring Configuration
Φ4 Φ7
Ring 1
Φ1
Φ2
Φ3
Φ4
Ring 2
Φ5
Φ6
Φ7
Φ8
Concurrency
Group
Concurrency
Group
Φ6
Φ1
Φ5
Φ2
General Ring Compatibility Rules
•Phases in same ring are NOT compatible (i.e. Φ1 and Φ2)
Φ3 Φ8
•Phases in separate rings ARE compatible (i.e. Φ1 and Φ5, Φ6)
•Phases are not compatible with phases in another concurrency
group (Φ1, Φ2, Φ5, Φ6 are NOT compatible with Φ3, Φ4, Φ7, Φ8)
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NEMA Highlights
• So, basically, a NEMA-based controller sequences
through the phases in a ring (or in parallel rings), while
determining what phases can be on with what other
phases.
• As long as phases follow the correct sequence and
compatibility rules, the factors that determine how “long”
a particular phase is on depends upon:
– The user definable phase parameters for each phase, and….
– Outside influences that may require a phase to end sooner than
normal, but no less than the minimum, like the need to serve a
coordinated plan (the green wave of lights down a street), or
emergency or transit preemption (a topic for later discussion).
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Interval-based
• The word Interval refers to an increment of
time within the cycle time (time it takes to
complete on complete rotation of the
signal plan).
• Many people refer to Interval-based
control as “Pre time”, but this is also
misleading (see section on Pre time vs.
Actuated). It is best to call it Intervalbased.
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Intervals
• Interval-based plans are typically programmed using a matrix
approach with Phases as one legend and Intervals as the other.
• Phases have no timings associated with them, but rather their activity
is dependent on the timings of the Interval or Intervals that they
belong.
• In the diagram below, the user would specify that the phase should
be green in Interval 1 and Amber in Interval 2. The times for each of
the Intervals would then be set up. All phases assigned to an Interval
are subject to the Interval time.
Interval
I-1
I-2
I-3
I-4
I-5
I-6
I-7
I-8
Φ
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Interval-based Timing Plan
• Sequence and Compatibility is dependent on the programming of the
timing plan. You basically tell the controller what to do and when.
I-1
I-2
I-3
I-4
I-5
I-6
I-7
I-8
Φ1
Φ2
Φ3
Φ4
Φ5
Φ6
Φ7
Φ8
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Pre time vs. Actuated
• Pre time means that the length of time and decision to
service a phase or not is predetermined and does not
change. It is part of the timing plan.
• Actuated means that the length of time and/or decision
to service the phase or not is variable based on demand
(i.e. detectors).
• Semi-Actuated is a mixture of the two approaches. Some
phases will be predetermined (a constant time and/or on
“recall”, which means always serviced regardless of
demand). Some phases will be demand driven.
– A good example of this is when a quiet side street intersects a
busy main road. The phases for the main road will always be
serviced each cycle, but detectors are installed at the side street
and it gets serviced (i.e. green signals) only when vehicles are
present.
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Pre time vs. Actuated (cont.)
• As you can see, Pre time is NOT the same
as Interval. You can have pre time and
actuated Interval traffic controllers and you
can have pre time and actuated NEMA
(so-called phase-based) controllers. The
terminology should be mutually exclusive.
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Summary
NEMA
Interval
Ring 1
Φ1 Φ2
Φ3
Φ4
Ring 2
Φ5
Φ7
Φ8
Φ6
•With Interval controllers You:
•With NEMA controllers You:
•Build the ring sequence
•Assign phase outputs to
Intervals 1, 2, 3, …etc.
•Assign concurrency groups
•Assign times to the Intervals
•Set-up phase parameters
• The controller does the rest
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•The controller runs your plan just
as you entered it
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NEMA
Interval
•Legacy controllers that were
NEMA style controllers are:
•Legacy controllers that were
Interval style controllers are:
•Honeywell HMC1000
•Transyt 1880EL
•TCT LMD40
•TCT LMD9200
•Semex C200
•Peek 3000/3000E
•Mulitsonics 820A
•Traconex TMP390/390CJ
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Is the ATC-1000 NEMA or Interval?
• The short answer is…….Both.
• This is the first controller that we know of that will do both methods
without having to change firmware to convert from one to the other.
• The ATC-1000 can change between the two traffic “engines” the
same way it changes between timing patterns. This can be done on
a schedule (time of day), by central override, or any other method of
changing patterns.
• This is helpful if there is a particular plan needed for an Intersection
that cannot be accomplished with the traffic engine used during
normal operations.
• Each traffic engine (NEMA and Interval) have their own feature sets.
They are basically like two traffic controllers living in the same box.
• It is very important to remember that just because the controller has
a feature in one traffic engine, it does not mean that it is in the other.
• The International version of the ATC controller will focus on adding
features to the Interval traffic engine, while most likely having a way
to disable the NEMA traffic engine to avoid confusion for those not
familiar with the NEMA methodology.
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ATC-1000
Two Controllers in One
NEMA Traffic Engine
Interval Traffic Engine
(Actuation Modes:
Pre time, Actuated, or Semi-Actuated)
(Actuation Modes: Pre time only)
Feature
s
NEMA side of
database complies
with NTCIP 1202 to
support NEMA
operation and
“standard” NTCIP.
Features not specified
by NTCIP are
proprietary.
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Switches
back and
forth based
on pattern
control
NTCIP Database
SGU- NEMA vs. Interval
Feature
s
Interval side of
database is all
proprietary. Though
we use the NTCIP
object (i.e. OID)
structure, NTCIP
does not specify
Interval operations.
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