National Electrical Manufacturers Association
Evolution of Controller Standards
The NEMA TS-1 traffic signal controller standard was developed in 1976, with the goal of providing interchangeability among manufacturers. All of the equipment and software necessary to support the controller operation was specified. A controller cabinet designed to house the controller and associated equipment was also specified, including all of the supporting wiring and configuration. The standard defined basic actuated intersection control, but did not specify hardware allowing controller capabilities to expand with technology.
Advances in technology and the desired functionality of the TS 1 controllers created several issues. The TS 1 standard focused on the three primary equipment connectors on the front on the controllers. Manufacturers independently added a fourth connector for preemption, coordination, additional detector inputs, and system communications that were not interchangeable, preventing enhanced controller functions. In some cases, system communications was not part of the fourth connector and was brought in through yet another connector. Additional limitations were identified with pretimed operations and capabilities beyond basic traffic control.
These limitations led to development of the TS 2 controller standard, developed in 1992. The TS 2 standard defined two types of controllers and cabinet architectures, the TS 2 Type 1 and TS 2 Type 2. The TS 2 Type 1 controller is unique in the sense that is uses an RS-232/SDLC data link connection to the peripheral devices, with a separate power connector (5). The TS 2 Type 2 provides the same connectors as the TS 1 but also includes the data link connector. This allows the TS 2 Type 2 controller to be installed in TS 1 cabinets, reducing the upgrade costs. The TS 2 standard defines advanced traffic signal operations such as coordination and preemption, and developed standards for pretimed operations and the cabinet. Advanced cabinet monitoring and diagnostics were defined.
Type 170 (non-NEMA)
The Type 170 controller standard differed from NEMA standards in that it was a hardware standard only. Software to run the controller can be supplied by independent vendors and designed to perform specific applications. Additional standards were developed for ancillary equipment in the cabinet, and the cabinet itself. The development of the Type 170 controller was an attempt to create a controller that could be used to meet current and future traffic needs. Rather than require hardware modification, as with NEMA controllers, the Type 170 responds to new or changing traffic conditions through upgrades or changes to the software. Nevertheless, some tasks do require hardware modifications and additions.
Several different configuration profiles were developed with the Type 2070 family, including the Type 2070N which is compatible with NEMA interfaces and cabinets. Some issues exist today with the Type 2070 platform, specifically related to the limited number of software vendors and the high cost of the controller hardware.
Current Practice: ATC
Current activities are focused on developing a new controller standard, coined the Advanced Traffic Controllers (ATC), which combines the best attributes of NEMA, Type 170, Type 2070 along with emerging ideas and technology. The new ATC platform will provide an open architecture, allowing for software portability. Open architecture will also provide additional applications, with the possibility of running multiple applications on one ATC controller. The ATC standard provides flexibility in hardware development, allowing hardware changes to evolve with technology. Interchangeability between manufacturers is strongly emphasized including connectors, user interface, software, communications, internal networks, and computer and modem modules. The flexibility developed with the ATC standards will allow an ATC controller to work in intersection control (including APS), real-time surveillance, transit systems, communications hubs, field masters, ramp metering, sign control, ITE beacons, video systems, environmental systems, and weigh-in-motion applications.
Typical Controller Cabinet Components
NEMA TS 1 and TS 2
Opening the door of a typical NEMA TS 1 controller cabinet will lead you to the controller itself, along with the conflict monitor, detectors, load switches, other peripheral equipment, and the necessary internal wiring. A circulating fan and filtered vent are included with each cabinet to provide air circulation to minimize heat buildup. A light is provided for working in the cabinet during nighttime hours.
The NEMA TS 2 controller assembly is nearly identical to the TS 1. The two primary differences are the change in controller unit and the conflict monitor is replaced by a malfunction management unit (MMU). The MMU is a more advanced device, not only monitoring all of the conflict voltages, but also communicating with the controller providing an additional element of monitoring. The TS 2 controller also uses a bus interface unit (BIU) for communication between the various control components and detectors. The BIU provides a simplification in cabinet wiring while providing flexibility and power (5). The TS 2 assembly contains a shelf-mounted power supply unit that provides the appropriate power to each of the controller devices. The detectors in the TS 2 cabinet are rack-mounted.
The controller unit itself simply sits on a shelf in the cabinet. Heavy cables run to each of the four ports on the front of the controller. The “A” connector provides power to the controller as well as inputs and outputs to the cabinet (5). The “B” and “C” connectors provide various inputs and outputs for control. The A, B, and C connectors are standardized by NEMA and are interchangeable amongst all manufacturers. Each connector is different, preventing cables from being inserted in the wrong connection port. The “D” connector provides communication, preemption, and expanded detection capabilities which are used in more advanced systems. Typical controllers have eight available detection inputs. The D connector provides input for eight additions detectors. The D connector is used with TS 1 controllers and is not standardized by NEMA, therefore, may not be interchangeable.
The conflict monitor (TS 1) is also shelf-mounted and wired into the controller system. The conflict monitor performs several very important functions, the most important of which is to prevent two conflicting green indications from being illuminated. The conflict monitor is really a voltage monitor, looking for inappropriate voltages in inappropriate locations or voltages that are above or below desired levels. The conflict monitor (5, 6):
Monitors the cabinet field wiring terminals for voltage on conflicting signal indications, focusing on one or more channels of 120-volt AC inputs (i.e., the green, yellow, red, and WALK); Monitors the should be on (standard feature only in NEMA conflict “absence of red” meaning if the green or yellow is not on, the red monitors); Monitors cabinet voltage to assure that the proper operating range is maintained; Monitors itself for proper supply voltage; May monitor intrachannel conflicts and short yellow timing; Does not monitor indication voltage to detect light bulbs that may be out unless all green, yellow or WALK bulbs on a channel burn out. Some agencies such as NYDOT require that a current monitoring feature be added to protect against burned out bulbs. The inductive loop detectors, or loop detector amplifiers, provide a direct connection to the inductive loops placed in the pavement. Vehicles that pass over the loops are identified by the loop detector amplifiers through changes in inductance. The detectors send vehicle detection information to the controller.
The flasher unit provides the flash sequence in the traffic signals. The flash sequence is implemented either during off-peak hours, most often during late night and early morning times. The flashers are also used when the conflict monitor overrides the signal system and puts the signals into a flash mode.
The Bus Interface Unit (BIU) links the Controller to the Cabinet input/output (I/O) elements (5). It can also be used as a detector interface device. The BIU is responsible for controlling load switches, providing dimming, receiving and isolating pedestrian calls, analyzing detector faults, time-stamping detector calls, and providing detector resets. By design, the BIU is free of operator controls. The BIU performs its I/O functions based upon a pre-wired card rack address.
The load switches receive output from the controller that relay to the terminals located near the bottom of the cabinet (5). Load switches receive a 12-volt DC input for the green, yellow, and red indications, and outputs 120 volts AC to the green, yellow and red field terminals.
Controllers satisfying TS 2 standards are categorized by Type 1 and Type 2 features (5). TS 2 Type 1 controllers contain high speed data channels and have increased capabilities, provide additional diagnostic data, and consume less power than the TS 1 controllers. TS 2 Type 2 controllers contain all of the features of the TS 2 Type 1, but also include additional connectors for data exchange with the terminals and facilities, and may contain a “D” connector for compatibility with TS 1 controllers.
Type 170 and Type 2070
The Type 170 and 2070 controller assemblies contain all of the same elements as the NEMA TS 1 (5). The controller itself, conflict monitor, detectors, load switches, peripheral equipment, and appropriate wiring are included. The controller assembly has a different look, using a rack-mounted modular setup. The controller assembly has more of a computer server look than the separate unit look of a typical NEMA setup. Detectors, power supplies, and preemption devices are modularly rack-mounted. The card rack for the input and output devices, called the input/output files, are mounted similarly.