Performance-Based Management of Traffic Signals (2020) / Chapter Skim
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Pages 121-150
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CHAPTER FOCUS Once an agency has identified signal performance measures to implement, staff will need to determine if their existing system can achieve those metrics or if new resources will need to be procured. Chapter 3 introduced some of the resources required for each signal performance measure, including data sources and detection.
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EXHIBIT 4-1. EXISTING RESOURCE CHECKLIST SYSTEM COMPONENTS COMMUNICATION
Communication available?
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4.2 DATA SOURCES There are two categories of data that will be explored in this guidebook: the external data sources that measure traffic performance without using information from a traffic signal controller and the internal data sources that capture traffic signal controller events. EXHIBIT 4-2 summarizes seven data sources (organized into internal and external data)
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The following information is provided as a "primer" for each data source. DESCRIPTION Detailed description of the data source.
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4.2.1 CONTROLLER HIGH-RESOLUTION DATA DESCRIPTION The data consist of timestamped events (and associated parameters) recorded at the nearest 1/10-second by the traffic signal controller.
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4.2.2 CENTRAL SYSTEM LOW-RESOLUTION DATA DESCRIPTION Volume and occupancy data have been available through central systems for many years. These data typically consist of volumes (vehicle counts)
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4.2.3 VENDOR-SPECIFIC DATA DESCRIPTION Many vendors provide data directly from their equipment, which can include detection systems, preemption systems, and adaptive control systems. Most of these systems are proprietary and require specific equipment and software.
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4.2.4 AUTOMATED VEHICLE IDENTIFICATION (AVI) DATA DESCRIPTION Automated vehicle identification (AVI)
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4.2.5 PROBE VEHICLE SEGMENT SPEED DATA DESCRIPTION The data are derived from analysis of individual probe vehicles, but the data are anonymized by converting individual vehicle positions into average segment speeds. The data are provided as speed records per segment over a specified time period (e.g., 1 minute, 5 minutes, 15 minutes)
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4.2.6 AUTOMATED VEHICLE LOCATION (AVL) DATA DESCRIPTION Automated vehicle location (AVL)
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4.2.7 CONNECTED VEHICLE (CV) DATA DESCRIPTION These data are defined by the SAE J2735 standard, which describes several data streams that will allow vehicles and infrastructure to communicate.
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4.3 TECHNICAL REQUIREMENTS This section focuses on the technical requirements for ATSPM systems, as summarized in EXHIBIT 4-5. In some places, the current infrastructure may already be able to support ATSPMs with marginal investments.
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4.3.1 LEVERAGING EXISTING EQUIPMENT The current capabilities of existing systems vary widely from one agency to another depending on the amount of resources that have been invested over time as well as how recently those investments were made. Every agency is unique and may face challenges in procurement, operation, or maintenance of new equipment.
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At a minimum, each subnetwork of traffic signal controllers should have one link to the central office to facilitate data transfer (Makovejs 2012)
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If communication to a central office is not possible (and the agency wants more data than can be stored on the controller) , the agency can use an embedded personal computer (PC)
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Advance and stop bar detectors that are tied together in a lane will not work for ATSPMs. If advance and stop bar detectors are tied together in a lane, they will need to be separated onto different detector channels to collect data for ATSPM reports.
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EXHIBIT 4-8. DETECTION REQUIREMENTS FOR SIGNAL PERFORMANCE MEASURES TYPE OF DETECTION AVAILABLE SIGNAL PERFORMANCE MEASURES None • 3.1 Communication Status • 3.2 Flash Status • 3.3 Power Failures • 3.18 Effective Cycle Length (7)
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EXHIBIT 4-9. EXAMPLE DETECTION LOCATIONS Note: Adapted from "UDOT Automated Traffic Signal Performance Measures" (Mackey 2017)
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4.3.4 DATA LOGGING REQUIREMENTS HIGH-RESOLUTION DATA Several options exist for obtaining highresolution data. All require that the IP address of the data logger be available so that data can be organized using an identifier.
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4.3.5 DATA STORAGE REQUIREMENTS HARDWARE Some physical components will need to be configured at a central office if an agency decides to use in-house equipment to facilitate the retrieval, processing, presentation, access, and archiving of the ATSPM data. Agencies can use a collection of one or more servers to host applications, services, and data pertaining to an ATSPM system.
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• NoSQL varieties, such as MongoDB, which store documents using dynamic schemas. • Cassandra, which is highly scalable and uses a hybrid key-value and column-store architecture.
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• Point-to-Point Tunneling Protocol (PPTP) • Layer 2 Tunneling Protocol (L2TP)
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4.4.2 DATA ARCHIVING Moving older data to an archive (i.e., through a logical or physical separation) can limit the size and improve the efficiency of an ATSPM system.
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4.5.2 DATA EXPORTING Many ATSPM systems have some capability to export data either into a flat file such as a comma-separated values (CSV) file or into tables and charts.
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4.6 REFERENCES 1. Bullock, D.M., C.M.
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