Terminology of Standards


The National Electrical Manufacturers Association (NEMA) is the association of electrical equipment and medical imaging manufacturers. NEMA provides a forum for the development of technical standards that are in the best interests of the industry and users, advocacy of industry policies on legislative and regulatory matters, and collection, analysis, and dissemination of industry data.


The NEMA Standards Publication, TS 4, “Hardware Standards for Dynamic Message Signs (DMS), with NTCIP Requirements”, was developed as a design and implementation guide for dynamic traffic messaging equipment that can be safely installed and provided to the end user with operational features based on current technology.
The goal of this standard is to provide the user with safe, dependable, functional, and easily maintained DMS Equipment.
The scope of the standard is to define the minimum hardware and functional characteristics of electronically controlled Dynamic Message Signs used for displaying messages to travelers.


EN12966 is European standard for Dynamic Message Signs. It has been prepared by Technical Committee CEN/TC 226 “Road equipment” under a mandate given to CEN by the European Commission and the European Free Trade Association, and supports essential requirements of EU Directive(s).
The main properties of DMS (such as optical performance, structural performance, etc.) are divided into classes. Based on the requirements of the project, the purchaser chooses different combination of classes.
The standard defines main properties of DMS, DMS testing methods, and factory production control methods. Informative annexes are provided as useful guidance on additional DMS aspects, helping those purchasing signs or signing systems.

NEMA TS-4 and EN 12966 comparison

Both NEMA TS-4 and EN12966 have the same purpose – they define performance parameters of LED displays (Variable Message Signs, Dynamic Message Signs) in all relevant aspects. NEMA TS-4 focuses on US client perspective, while EN12966 focuses on European client perspective.
Although they are not exactly the same in scope and content, they concur in important parameters like legibility.

EN12966 certification is mandatory in European Union - no LED displays can be installed on the road if not certified.

NEMA TS-4 is not mandatory in USA.


CE label is mandatory for Dynamic Message Signs sold and installed in the European market. The CE label can be affixed to a VMS only if the equipment has passed the rigorous EN12966 compliance testing.
CE certificate is verifying that all mandatory tests have been passed, and that specific quality classes have been approved. The tested class combinations are acknowledged in the CE certificate.
EN12966 test reports are the mandatory part of the accompanying CE-Certification documentation.


NTCIP is a group of communications standards for transmitting data and messages between microcomputer controlled devices used in Intelligent Transportation Systems (ITS).

A set of NTCIP standards define all relevant aspects of Variable Message Signs (Dynamic Message Signs) communication. Including, but not limited to:

NTCIP 1101 – Simple Transportation Management Framework:

  • NTCIP 1102 – OER Base Protocol
  • NTCIP 1103 – Transportation Management Protocol
  • NTCIP 1201 – Global Object Definitions
  • NTCIP 1203 – Object Definitions for DMSs
  • NTCIP 2101 – PMPP Using RS-232 Subnetwork Profile
  • NTCIP 2102 – PMPP Using FSK Subnetwork Profile
  • NTCIP 2103 – Point-to-Point Protocol over RS-232 Sub-Network Profile
  • NTCIP 2104 – Ethernet Sub-Network Profile
  • NTCIP 2201 – Transportation Transport Profile
  • NTCIP 2202 – TCP/IP and UDP/IP Transport Profile
  • NTCIP 2301 – STMF Application Profile

Dynamic Message Sign (DMS)

DMS are electronic LED sign with full matrix or line matrix of pixels, in full color (Red/Green/Blue - RGB) or monochromatic (amber or white).

Matrix is a collection of equally distanced pixels arranged into a fixed number of rows and columns. Full matrix Dynamic Message Sign has the entire visible area covered with matrix of pixels. Full matrix DMS’s are suitable for displaying texts and images, and combination of both. Line matrix Dynamic Message Sign has multiple matrices of pixels so called “line matrices”. Each line matrix is intended to display one line of text. Line matrix Dynamic Message Signs are suitable for displaying text messages only.

VMSs are used on highways, roads and in tunnels to display traffic-related messages to drivers. VMS messages contain multiple lines of text and/or images, ranging from speed limit, to advisory messages.

The term Variable Message Signs is interchangeable with Dynamic Message Sign (DMS) or Changeable Message Sign (CMS).
There are several different versions of DMS:

  • Lane Control/Use Signs (LCS/LUS) - usually smaller in size, used to navigate the drivers in each lane,
  • Side-mounted Dynamic Message Signs (SDMS) - usually bigger than LCS, used for informing drivers through text message or images
  • Walk-in VMS - large signs with line matrices or full matrix, amber or full color, used to transfer information through text or images

Lane Control Sign (LCS) / Lane Use Sign (LUS)

LCS are usually smaller in size, mounted above each traffic lane. They usually display traffic symbols used for managing lanes such as green straight arrows for open lane, yellow rotated arrow for drivers to merge out of the lane they are in, red cross for closed lane, and speed limits. Other graphics or text is possible.

Side-mounted Dynamic Message Sign (SDMS)

SDMS are usually mounted on the side of the highway. They usually display text messages or graphics (i.e. speed limit).

Walk-in Dynamic Message Signs

Walk-in DMS is a large DMS with a large, walk-in housing. Enables maintenance personnel to enter inside the housing and perform maintenance activities in secured environment.
It has the same display capabilities as regular VMS/DMS/CMS.





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