NEMA Traffic Controller Basics

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This page is a work in progress. The intent is the break down NEMA for those new to it.

Items to be covered:

Differences between NEMA TS1, TS2 Type 1, and TS2 Type 2.

General cabinet sizes such as G, M, Stretch M, P and R

Cabinet plug ins such as the controller, monitor, detectors, backpanel, switchpacks, etc.

Various terminology such as phasing, rings, timing parameters, detector options

More to come soon...


This guide is intended to be basic and straightforward for those who are new to NEMA traffic controllers and the terminology. Items will be broken down and simplified as much as possible. (PHOTOS COMING SOON!)


The first of the two major Technical Specifications. TS-1 standardized the large A B and C harness pinouts, the electrical design for the switching equipment. It is the most common amongst enthusiasts. TS-1 was developed in the 1970s. They are known for their simplified point-to-point wiring technique which makes them easy to troubleshoot. They fell short when it comes to customization. TS-1 has limits dependent on the cabinet and the available I/O connections.


The second of the two major Technical Specifications. This standardized detection, communications, and introduced a serial datalink communication line (SDLC), also known as the serial data bus to communication with equipment in the cabinet. NEMA TS2 was developed in the mid 1990s, and was broken into two sub-components: TS-2 Type 1 and TS-2 Type 2.

TS-2 Type 1: The less common of the two sub-components of the TS-2 standard. This version required that all equipment in the cabinet be able to communicate on the serial data bus. There are no large A, B, C harnesses with the exception of A for power input to the controller. The monitoring devices retain the TS-1 harnesses for conflict and voltage monitoring but are also communicating on the data bus. Type 1 cabinets were popular for their simplified wiring, and no direct I/O connections. But they were more difficult to troubleshoot problems due to the less point-to-point wiring.

TS-2 Type 2: The most common of NEMA cabinets in the field. This standard is a hybrid of TS-1 and TS-2 Type 1. It retains the A, B, C cabling for the I/O to the backpanel, however monitoring and detection are on a serial data bus for simplified wiring and easier troubleshooting.

Cabinet Sizes and Types

Controller Units and Timing

Intersection Monitoring Units

Detector Equipment

See main article Vehicle Detection Methods...

With all NEMA controllers (and most 2070/150/332 controllers), controllers watch input lines (detector inputs), and when those detector lines are connected to ground (brought low), the controller sees that detector as active.

Bringing the input line low can be done in several ways -

  1. In TS1 and TS2-2, the input is usually drawn low by a relay connected to the detector system. (Loop amplifier, Video CPU, etc.)
  2. In TS2-1, detector status is reported through the SLDC Bus, with the BIU's reporting status information from the detector cards.

Overview of Cabinet Facilities

Switching Equipment

Troubleshooting Help