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?
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?
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?
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?
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.
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.
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.
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).
- 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).
Detectors
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.
- 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.
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.
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.
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).
- 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.
