Frequently Asked Questions
for the ACS-Lite
The following list of Frequently Asked Questions
includes questions and answers on a number of topics related to the
Adaptive Control Software Lite (ACS-Lite).
Signal Timing
- Was traffic signal timing optimized on the four test
site arterials prior to the deployment and testing of the ACS-Lite?
- Will ACS-Lite effectively manage saturated flow situations?
- Does the ACS-Lite System archive signal timing for
later use?
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Hardware
- Who supplies the ACS-Lite field processor and how
much does it cost and has it been tested to National Electrical Manufacturers
Association (NEMA) TS2 environmental specifications?
- Is it possible in the future to have more than 12
intersections without the Internet Protocol (IP) communications?
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Detectors
- Does the size of the loops used for vehicle detection
affect the operation of ACS-Lite?
- Are the local detectors used phase actuation also
used by ACS-Lite to perform phase split tuning functions?
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Software
- Are the algorithms and software developed with FHWA
funding readily available? If so, where?
- Is there a logic identifying detector errors and a
plan B under such conditions?
- How does ACS-Lite handle incidents?
- Does ACS-Lite have algorithms for arterials in both
directions (like CBD's in both east-west and north-south directions)
or it is currently implemented only for one direction of travel?
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Signal Timing
- Question: Was traffic signal timing optimized
on the four test site arterials prior to the deployment and testing
of the ACS-Lite?
Answer: No, signal timing on each of the four arterials
where ACS-Lite was tested was not updated prior to the implementation
of the ACS-Lite. Since ACS-Lite works to update and optimize existing
timing it might prove beneficial to implement the most recent timing
available prior to implementing ACS-Lite.
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- Question: Will ACS-Lite effectively
manage saturated flow situations?
Answer: There are no specific features of the ACS-Lite
algorithms that manage the system differently when all approaches
to an intersection are over-saturated. The split tuning algorithms
are designed to move available time from phases that are under-saturated
to phases that are over-saturated. A goal of the ACS-Lite (as well
as all adaptive control systems) is to prolong the time before saturated
conditions occur and recover faster from saturated conditions once
they have happened. In the near future, the ACS-Lite system will be
enhanced to adapt (increase) the cycle time to better handle saturated
conditions.
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- Question: Does the ACS-Lite System
archive signal timing for later use?
Answer: ACS-Lite stores all second-by-second phase
timing data, detector data, and its control decisions for later analysis
for up to one month.
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Hardware
- Question: Who supplies the ACS-Lite field
processor and how much does it cost and has it been tested to National
Electrical Manufacturers Association (NEMA) TS2 environmental specifications?
Answer: The controller manufacture will supply
a hardened field processor that meets the NEMA TS2 environmental specifications.
The cost of the processor will be similar to the cost of a high-end
personal computer (PC).
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- Question: Is it possible in the
future to have more than 12 intersections without the Internet Protocol
(IP) communications?
Answer: ACS-Lite is capable of supporting more
than 12 controllers on a serial communications channel that is faster
than 9600 bits per second (bps).
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Detectors
- Question: Does the size of the
loops used for vehicle detection affect the operation of ACS-Lite?
Answer: The size of the loop is not critical to
the performance of the algorithms. Standard loop designs (e.g., 6
foot advance loops/zones, 20-40 feet stop bar loops/zones) have performed
adequately for all field tests. Better performance will be achieved
with detection zones that are separated out by lane-by lane, but it
is not necessary that the zones are separated by lane.
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- Question: Are the local detectors
used phase actuation also used by ACS-Lite to perform phase split
tuning functions?
Answer: Yes. The same detectors that are used to
operate the intersection are used for collection of the data for phase
tuning.
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Software
- Question: Are the algorithms
and software developed with FHWA funding readily available? If so,
where?
Answer: The software will be available through the
participating traffic signal controller manufacturers: Siemens, Econolite,
Peek, and McCain.
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- Question: Is there a logic identifying
detector errors and a plan B under such conditions?
Answer: The identification of detector errors/diagnostics
is a function of the controller. Upon receipt of a detector error
message (e.g., max presence, erratic, or no activity) from the controller,
ACS-Lite will remove/neglect that detector from its calculations.
When the detector is repaired and starts reporting correct data again,
the information is automatically re-introduced into the calculations.
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- Question: How does ACS-Lite handle incidents?
Answer: Acs-Lite handles incidents by modifying
the splits and offsets of the traffic pattern (and in the future -
cycle time) to adapt to the increases and decreases in traffic flows
on the facility it is managing. Detector diagnostics/failure conditions
are the responsibility of the controller software (e.g., stalled vehicle
in a left-turn bay). ACS-Lite currently has no component for tactical
modification of phase durations using hold and force-off commands
(e.g., truncating phases due to downstream flow restrictions).
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- Question: Does ACS-Lite have
algorithms for arterials in both directions (like CBD's in both east-west
and north-south directions) or it is currently implemented only for
one direction of travel?
Answer: Currently, ACS-Lite can handle only one
offset value per pattern but any number of phases can be designated
as progression phases. Enhancements to the algorithms to deal with
grid systems are planned for future work.
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