An Overview of ITS Standards and Protocols

By Raman K. Patel and Edwin Rowe

Importance of Standards | Standards and Protocols Concepts | Objectives and Criteria for Standards

NTCIP Standard | Standards Development Organizations | National ITS Architecture | ITE's Role in the Standards Process

ITS America's Role in the Standards Process | Conclusion | Bibliography


The advent of intelligent transportation systems (ITSs) has created a pressing need for new standards and protocols to provide for interoperability, compatibility and interchangeability. Interoperability standards would, for example, allow for a vehicle with appropriate radio equipment to travel anywhere in the country and receive transmissions containing information on congestion and incidents. Compatibility will allow different devices to communicate over the same communications medium without generating interference with one another. Interchangeability would allow the replacement of traffic controllers from different manufacturers within the same traffic signal system.

Twenty-nine ITS user services involving communications to and from vehicles or travelers have been identified to date. These user services are multimodal in nature and have significantly altered the manner in which transportation agencies will conduct their operations in the future. Because multimodal user services are to be implemented within an integrated ITS, a multitude of new devices and their interfaces must be developed and linked together. Standards will make possible the implementation of packages of user services forming advanced traffic management systems (ATMSs), advanced traveler information systems (ATISs), advanced public transportation systems (APTSs), commercial vehicle operations (CVO), advance rural transportation systems (ARTSs), and advanced vehicle control systems (AVCSs).

Companies who in the past have supplied their customers with equipment and systems utilizing proprietary standards will find it necessary to convert to open systems standards in order to meet the requirements of the national ITS program, as set forth by federal, state and local transportation agencies. The lack of ITS standards is already impeding the deployment of ITS in North America. On one hand, purchasers of ITS do not want to be locked into proprietary systems that will not provide long-term interoperability, compatibility and interchangeability. On the other hand, vendors are reluctant to make major capital commitments to new ITS products until the uncertainty over standards is resolved.

The purpose of this article is to broaden awareness of the requirements for ITS standards and to encourage ITE members' participation in the standards development process. It is particularly essential that users of ITS systems provide more input into the standards setting process than they have in the past.


Importance of Standards

The development of standards will make possible the high degree of integration required to make ITS a reality. The ITS program will open up new markets for products on a national and eventually international scale. The establishment of standards will make it easier and less costly for users to upgrade their systems as new features become available.

ITS is a national program that will utilize a variety of advanced technologies that are integrated to provide 29 user services organized into seven service bundles. All of these services depend upon uniform "connecting standards" for subsystems across and within service bundles. To provide a framework for the development of standards and protocols, the U.S. DOT is sponsoring the ITS National Architecture Project. The Architecture project will identify where standards are needed to promote future ITS deployment.

The development of nationwide standards should improve overall product design and performance, safety, and ease of operation and maintenance. ITS standards also should boost consumer confidence, because new ITS products would be more likely to retain their value and cost less to upgrade as new add-on features become available. In the long run, adoption of standards will result in reduced costs for ITS deployment.

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Standards and Protocols Concepts


According to the 1979 National Policy on Standards for the United States, standards can be defined as a prescribed set of rules, conditions or requirements concerning definition of terms and classification of components; specification of materials, performance or operation; definition of procedures; or measurement of quantity and quality in describing materials, products, systems or practices.


A protocol is defined as a set of rules or conventions formulated to control the exchange of data between two entities desiring a connection. Protocols are required to define the exchange of control information between user device and the network. Basic elements of a protocol include data format and signal levels, control information coordination and error handling, and timing.

System Architecture

A system architecture constitutes the framework that describes how system components interact and work together to achieve total system goals. It describes the system operation, what each component of the system does, and what information is exchanged among the components. An architecture can be either "open" or "closed." The National ITS Architecture under development provides for an open system that will support a multivendor environment allowing for compatibility, interoperability and interchangeability. This architecture does not prescribe standards and protocols but rather identifies where they are needed to obtain the stated objectives.

An example of the interplay between system architecture, standards and protocols is the development of a unified strategy for variable message sign (VMS) messages by the I-95 Northeast Corridor Coalition of more than 30 transportation agencies. The emerging "open system" NTCIP standard will allow for the display of the same message content on different types of VMSs purchased from different manufacturers, and operated by different public agencies.

Open Standards

Not too long ago, the standards established in the computer industry were limited primarily to the computer's internal operations or the connection to local peripheral devices. Computer networking could take place only within a single environment resulting in closed systems based on proprietary communications protocols. Users increasingly became dissatisfied with this situation, which generally locked them into one major vendor of computer equipment. To facilitate the development of open standards, the computer and communications industries have responded with the Interna-tional Organization for Standardiza-tion's Open Systems Interconnection Reference Model (RM-OSI). This model contains seven layers that build upward from a base physical layer, as shown in Table 1.

Table 1. Open Systems Interconnection Reference Model

Layer 1 - Physical: Defines mechanical and electrical interfaces and the transmission medium.
Layer 2 - Data Link: Defines methods for ensuring data integrity (such as error correction).
Layer 3 - Network: Defines how packets of data are routed from source to destination.
Layer 4 - Transport: Defines the organization of data passing to and from the lower layers. Involves breaking longer messages into packets for transmission.
Layer 5 - Session: Defines the procedure for different communications equipment to establish dialogues.
Layer 6 - Presentation: Defines the syntax and semantics of transmitted information.
Layer 7 - Application: Defines procedures for file transfers, access methods and management of messages.

These layers are generally viewed as forming two distinct groups that functionally support open communications: Layers 1-4 define data transport, and Layers 5-7 define data processing.

In developing a protocol structure for communications between a specific group of devices, the RM-OSI does not require an explicit protocol in each layer, if the functionality of that layer is not needed. For example, in the case of the NTCIP, the proposed protocol stack currently is satisfied within layers 1, 2, 3 and 7.

A basic organizing principle of RM-OSI is layer independence. This allows for the substitution of alternative protocols approved for use within a layer without affecting adjacent layers, as long as there is a consistent interface along the boundaries.

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Objectives and Criteria for Standards

The new standards under consideration by the ITS community build on established communication and computer industry standards. Objectives and criteria for establishing the new standards for ITS are shown in Table 2.

Table 2. Objectives and Criteria for New ITS Standards

  • Expandability: Open ended; allows upgrading to take advantage of continued evolution in transportation information and control systems.
  • Interoperability: Machine independent; allows the largest-possible markets for deployment.
  • Compatability: Noninterference; various devices within the same system must be able to operate without interfering with the operation of other devices.
  • Interchangeability: Vendor independent; devices from different vendors that perform the same functions may be interchanged.
  • Open: Nonproprietary; promotes rapid development of new technologies and acceptance by consumers.
  • Scaleable: Flexible; standards recognize local conditions with a wide range of ITS devices and communication channel capabilities. Legacy systems are accommodated to the extent possible.
  • State-of-the-art: Use of the best available standards to avoid locking in obsolescent technologies.

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NTCIP Standard

One of the most important standards that will affect ITE members is the NTCIP, or National Transportation Communications/ITS Protocol (see related article, Page 36). NTCIP will define how traffic management systems will communicate with each other and with ITS field devices such as traffic signal controllers, variable message signs and highway advisory radio. Development of the NTCIP has been a multiyear cooperative effort of users, system integrators and manufacturers of signal equipment. Transportation agencies make frequent requests for a communications standard that will allow the purchase of signal equipment from multiple vendors over a system's life. In response, the National Electrical Manufacturers Association (NEMA) began discussions in 1992 to design a communications protocol for a new generation of NEMA controllers. In May 1993, the FHWA sponsored a symposium to encourage this NEMA initiative and to bring system users, system integrators and Type 170 controller manufacturers into the process. The NEMA Technical Committee has met every few months since then to produce a draft standard. A second FHWA-sponsored symposium was conducted in February 1995, and a steering committee composed of a representative group of system users and system integrators was formed to serve in a review and advisory capacity. These committees have now accelerated their efforts towards the development efforts for NTCIP.

Initially, the NTCIP was designed only for communication between traffic management centers and traffic signal controllers. Subsequently, FHWA encouraged broadening the protocol to include additional types of system field devices such as VMS, camera control, ramp metering and traffic management centers. A draft NTCIP document has been distributed for comment, and a final version is anticipated for submittal to NEMA Standards approval by the end of 1995. Development of prototype software implementing the NTCIP is under way and scheduled for delivery of alpha level code by the end of the year.

A remaining major issue to be decided involves the selection of a communication protocol. Again, a widely used and well-supported common protocol is needed for ITS deployment. The protocol developed by the telecommunication industry known as X.25 was originally recommended and is in the recently distributed NTCIP draft. Subsequently, the steering group has recommended consideration of the commonly used Transmission Control Protocol/Internet Protocol (TCP/IP) instead of X.25. TCP/IP is the same open system (vendor independent) standard that is used for communications on the Internet.

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Standards Development Organizations

The development of standards has been a major factor in the rapid deployment of new products and services by the worldwide computer and telecommunications industries during the past several decades. Standards organizations are of two types: treaty-based and voluntary.

The treaty-based organization is the International Telecommunication Union (ITU), founded under the International Telecommunications Convention (ITC). ITU membership consists of Japan, Australia, Canada, the United States and all nations currently involved in ITS in Western Europe. This Geneva-based organization acts through two technical organizations - the International Consultative Committee for Telegraph and Telephone (CCITT) and the International Consultative Committee for Radio (CCIR).

The voluntary organizations are the International Standards Organization (ISO) and the International Electromechanical Commission (IEC). These organizations, also based in Geneva, work in close cooperation with the CCITT and CCIR. Most industrialized countries are members of these voluntary standards organizations and are represented by their national standards body, trade associations, professional associations and government representatives. The American National Standards Institute (ANSI) serves as the voting member of ISO for the United States.

The three major international bodies actively developing standards for computers and communications are the ISO, Institute of Electrical and Electronic Engineers (IEEE) and CCITT. The ISO and IEEE develop standards for use by computer manufacturers, while CCITT develops standards for connecting equipment to different types of national and international public networks. As the overlap between the computer and telecommunications industries increases, however, there is of necessity an increasing level of cooperation between these organizations.

The ISO, with a membership of more than 90 countries, has developed more than 7,500 voluntary standards through more than 160 technical committees. The ISO standards are voluntary and are intended for worldwide application to remove barriers to international trade.

Regarding ITS-related standards, ISO has formed Technical Committee 204 (TC204) on Transport Informatics and Control Systems. In support of TC204, ITS America has taken the lead in the United States. In Japan, the Japanese National Committee of ISO TC204 has been formed. In Europe, the CEN/TC 278 Road Transport and Traffic Telematics organization closely coordinates its activities with TC204.

Within the ISO TC204, there are 15 international working groups (WGs) addressing ITS needs for standards:

  • WG 1: Architecture
  • WG 2: Quality and Reliability Requirements
  • WG 3: TICS Database Technology
  • WG 5: Fee and Toll Collection, Man-agement and Access Control
  • WG 6: General Fleet Management
  • WG 7: Commercial/Freight Management
  • WG 8: Public Transportation/ Emergency
  • WG 9: Integrated Transport Informa-tion Management and Control
  • WG 10: Traveler Information Systems
  • WG 11: Route Guidance and Navigation Systems
  • WG 12: Parking Management/Off-Road Commercial
  • WG 13: Man Machine Interface
  • WG 14: Vehicle Control Systems with External Interfaces
  • WG 15: Dedicated Short-Range Communications
  • WG 16: Wide Area Communications Protocols/Interfaces

In the United States, the following trade and professional organizations are expected to contribute to the development of ITS standards:

  • NEMA
  • Society of Automotive Engineers (SAE)
  • Electronic Industries Association (EIA)
  • IEEE
  • Telecommunication Industries Association (TIA)
  • VMEbus International Trade Association (VITA)
  • ITS America - Standards and Protocol Committee
  • ITE ITS Council Standards Committee
  • American Association of State Highway and Transportation Officials (AASHTO)
  • American Society for Testing and Materials (ASTM)
  • Institute of Navigation (ION)

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National ITS Architecture

A key objective of the National ITS Architecture project is to achieve national interoperability of certain ITS services; this will require the establishment of national standards. To this end, the Architecture project is producing three major products that deal with ITS standards. The first product is a series of white papers on standards needs, the standards development process, example requirements, and an architecture reference model. These white papers are intended to provide an opportunity for consensus-building and receiving feedback from the ITS community.

The second product, to be delivered in the summer of 1996, is a standards requirement document (SRD). This will provide an architecture reference model containing definitions of interfaces and necessary priorities for the standardization process. Requirements packages requiring further action will also be generated. The third product, a standards implementation plan (SIP), will outline the standards, time schedule and critical milestones for the implementation phase.

So far, the National Architecture Program has examined 72 interfaces for possible standardization; 28 interfaces have been identified as deserving a high priority for standardization.

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ITE's Role in the Standards Process

ITE's activities in the ITS standards process has been geared to address the core questions and issues facing ITE members, including:

  • The effective designing and integrating of ITSs.
  • Selecting and installing equipment to deliver service efficiently.
  • Compliance by government owners and vendors with environmental and quality standards for temperature, power, humidity and vibration related to ITS network components so performance will be at par.
  • Setting national standards and guidelines in the following areas to simplify operations and maintenance of ITS networks: field equipment, environmental parameters, quality control, ATMS design criteria, software applications, documentation, and training and education.

ITE is undertaking a series of efforts to ensure that transportation and traffic engineers are informed and integrally involved in the development, adoption and review of ITS standards. With financial assistance from the U.S. Federal Highway Administration, these efforts include:

  • Serving as the administrator of the U.S. Working Advisory Group 9 (WAG9), which is responsible for generating U.S. input to ISO TC204 efforts to develop international ITS standards in traffic and travel management.
  • Providing travel assistance to ensure that the United States is represented by technical experts at international meetings dealing with ISO ITS standards.
  • Providing travel assistance for transportation engineers employed by public agencies to attend and participate in standards development activities.
  • Conducting meetings and workshops, and providing written comments and input from the transportation engineering community to the developers of standards and protocols.
  • Providing review and comments to the development of the U.S. National Architecture.
  • Making the latest versions of the NTCIP available for review (Page 36 of this issue. Also see the ITE electronic bulletin board, 202/863-5487 or 202-863-0046, and the ITE Internet home page at
  • Providing review and comments throughout the NTCIP development process.
  • Providing leadership in the development of the ITS urban core infrastructure, which will tie in with broader aspects of National ITS Architecture, standards and NTCIP. ITE also has been the leader in emphasizing the importance of ITS operation and maintenance funding issues and related guidelines.

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ITS America's Role in the Standards Process

The ITS America Standards and Protocols Committee coordinates the development of ITS-related standards. The Council of Standards Organizations is a subcommittee with representatives from all ITS-relevant standards developing organizations (SDOs) that meets frequently to coordinate SDO activities. Other subcommittees of the Standards and Protocols Committee include Map Database and Information Systems, Hazard Analysis, Electronic Fee Payment, Control and Control System Interface, and Standards Catalog.

ITS America also supports the work of SDOs by developing consensus for proposed standards when necessary. The ITS America Coordinating Council recently approved a process for developing consensus for standards requirements. This process was followed in 1994 and early 1995 to generate the Electronic Toll and Traffic Management (ETTM) User Requirements of Toll Authorities for Future National Interoperability. ITS America currently is leading an effort to develop vehicle-to-roadside communications requirements for commercial vehicle operations.

ITS America's Standards and Protocol Committee and FHWA have jointly produced a standards and protocol catalog containing 268 entries (Publication No: FHWA-JPO-95-005). This is a useful guide to the current state of ITS standards development and future direction.

ITS America also serves as the U.S. Technical Advisory Group to ISO Technical Committee 204 on Transport Informatics and Control Systems. In this role, ITS America convenes representatives of the ITS community in the United States and develops positions for items before the ISO TC204. Currently, TC204 subcommittees have 25 work items before them that could ultimately lead to international standards.

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While this article's major intent has been to inform ITE members on the role and importance of standards in the national ITS program, it is also hoped that a representative cross-section of ITE members involved in ITS will actively participate in the standards- setting process. In particular, greater participation from public agencies is needed - industry, consultants and system integrators already are well represented. For those who are interested in this subject, the following options are suggested for your consideration:

  • Join ITE Standards Committee of the ITE ITS Council.
  • Join ITS America Standards and Protocols Committee.
  • Notify ITE headquarters of your interest in reviewing the NTCIP standard.
  • Notify ITE headquarters of your interest in reviewing the reports of the National Architecture Program.

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National Program Plan. ITS America/U.S. DOT: March 1995.
A Review of NTCIP Development. Paper by Steering Committee Group, May 5, 1995, FHWA Cover Letter.
Standards and Protocols Catalog. Robert Barrett, JPL, U.S. DOT, FHWA: March 1, 1995.

Raman K. Patel, P.E., is a Technical Coordinator for I-95 Northeast Corridor Coalition and is on loan from the New York City Department of Transportation. He holds a B.E. and a master's in electrical engineering. He serves on the NTCIP Steering Committee and is a member of the ITS Executive Council. A Member of ITE, Patel is Chairperson of ITE's Standards Committee.

Edwin Rowe, P.E., is CEO of Gardner-Rowe Systems Inc. He was formerly General Manager of the Los Angeles Department of Transportation, where he was employed for 35 years. Rowe is a Member of ITE and a recipient of ITE's Theodore M. Matson Award. He is the incoming Chairperson of the ITS Council.

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