This Fact Sheet was written on September 21, 2009. The status of the standard at the time was: Published on November 12, 2008.
This Fact Sheet was written on September 21, 2009.
The status of the standard at the time was:
Published in November 2008.
This Fact Sheet was last verified on September 25, 2009
Data dictionaries and message sets are essential components in the operation of computer-based intelligent transportation systems (ITS). Data dictionaries provide the basic definitions, generally described as data elements (DEs), that make up the specific content of a message used to convey information among ITS systems. In a simple analogy, messages are the sentences and DEs are the individual words. A message set provides a series or set of individual messages, established in a strict format, for exchanging information on a given topic. Thus, an agreed-upon data dictionary and message set with unambiguous definitions are essential to exchange information between, for example, traffic management centers (TMCs) or between a traffic management center (TMC) and other ITS centers and/or suppliers of traffic-related information.
Message sets and data dictionaries work in conjunction with another type of standard that provides the actual communications protocols. Protocol standards describe how messages are encoded for transmission and then transmitted and received by other systems.
The data dictionary and messages set standard, AASHTO-ITE TM 2.1, Standards for Traffic Management Center-to-Center Communications, was developed for ITS systems that manage traffic. (The data dictionary standard, AASHTO-ITE TM 1.03, Traffic Management Data Dictionary (TMDD), and its companion message set standard AASHTO-ITE TM 2.01, Message Set for External Traffic Management Center Communications, were combined into the single standard, AASHTO-ITE TM 2.1, Standards for Traffic Management Center-to-Center Communications, which was updated to version 3.0 in November 2008.) These data elements and message sets were developed as a joint AASHTO-ITE effort under the oversight of a national steering committee composed of formal representatives of both organizations. More information concerning this standard can be found at https://www.ite.org/technical-resources/standards/tmdd/.
The AASHTO-ITE TM 3.0, Standards for Traffic Management Center-to-Center Communications standard is comprised of two volumes: Volume 1: Concept of Operations and Requirements and Volume 2: Design Content. The standard is intended to be independent of the underlying communications protocols used to carry the messages it defines.
The Concept of Operations and Requirements document defines the user needs addressed by the standard, and the functional requirements necessary to meet those needs. It defines the operational environment for traffic management, and the operations required to realize those needs in an operating center.
The Design Content document defines the design content that realizes the functional requirements, and includes dialogs, messages, data frames, data elements and object classes. Collectively these constructs support the data exchange within and among traffic management systems. Dialogs are modeled as Universal Markup Language (UML) sequence diagrams. Messages, data frames and data elements are defined using both ASN.1 and XML. Object classes are defined in ASN.1 only. Altogether, this document defines the schema of all traffic management communications necessary to implement any of the needs defined in Volume 1.
This standard should be used by transportation, traffic, and system engineers involved with the design, specification, procurement, installation, operation, and maintenance of traffic management systems. ITS system software designers and application developers should find this standard especially relevant to their efforts.
The traffic management functional area data dictionary (as distinguished from an application-specific data dictionary) provides a national standard for an agreed-upon set of data elements(DE) traffic management systems. Similarly, the message set provides a national standard for messages involving traffic operations. The data dictionary and message set become the basis for design and implementation of traffic management communications. Typically, these standards will be implemented in an Applications Program Interface (API) allowing communication to and from the traffic management center or application. Thus, the data dictionary and message set defined in this standard are intended to act as the core set of DEs and the core sets of messages, respectively, that will be used by all ITS-based traffic management systems. Both the data dictionary and message set may be augmented in specific applications as necessary to support additional local functions or conventions not contained in the standards.
The traffic management messages and DEs should be implemented in conjunction with the selected center-to-center communications profile standards. In addition, an interface specification should be defined consistent with the AASHTO-ITE TM 3.0,Sandards for Traffic Management Center-to-Center Communications standard.
The data dictionary and message set included in AASHTO-ITE TM 3.0, Standards for Traffic Management Center-to-Center Communications was based on the logical and physical information flows supporting the "Manage Traffic" function as described in the National ITS Architecture. The standards consist of two volumes, including:
Volume I: Concept of Operations and Requirements
Volume II: Design Content
A database format of the messages and data elements is also available.
The Concept of Operations and Requirements organizes content by need. It addresses connectivity, authentication, meta-data, handling of events, provision of roadway data, control of field devices, and data archival.
The Design Content is organized by design construct and then by relevant information type. Design constructs are dialogs, data frames, messages, data elements and object classes. These constructs work together to form the information exchange format, and must be considered in context of the entire service to be delivered. Within each construct, (data elements, data frames etc.) the schema are organized around field device types, such as CCTV and Intersection Controllers.
Previous versions of this standard were organized differently; for the most part this version of the standard is not backwards compatible.
The following ITS standards are related and should be considered when using this standard: