Connecting traffic management centers will help motorists move across Texas.
Intelligent Transportation Systems (ITS) can improve traffic flow, estimate freeway travel time and increase safety by alerting drivers to potential hazards and traffic accidents. Many U.S. cities use these systems to help reduce traffic and minimize accidents. Very rarely do these cities have systems that are integrated with other areas in the same region. Southwest Research Institute (SwRI) staff are integrating ITSs and also providing strategic planning and services to help systems meet national standards.
Currently, SwRI is connecting dissimilar traffic management centers (TMCs) across the state of Texas. The development of standards to support center-to-center communications has been the focus of two transportation systems standards groups: the Traffic Management Data Dictionary Committee and the National Transportation Communication for ITS Protocol Center-to-Center Working Group. These groups have developed standards that can be used to allow traffic centers to exchange data, including command and control as well as status information.
In 1999, the Texas Department of Transportation, along with the Federal Highway Administration, initiated a program to develop a "center-to-center" communications infrastructure that would apply ITS national standards to allow separate traffic management centers to exchange data. These systems were generally implemented using different software codes. A major criterion of this program is to develop an extensible architecture that allows these centers to seamlessly exchange data and to support additional functionality, such as transit or parking information. SwRI used this architecture to develop a backbone for the exchange of ITS data among traffic management centers throughout Texas.
The goals of the center-to-center infrastructure development effort include using the ITS national architecture; transferring, storing and displaying traffic conditions; exchanging data among advanced traffic management systems in Texas; and providing an infrastructure to support future exchange of ITS data.
A development effort is under way to implement a foundation that supports both the current requirements for traffic management and the envisioned future requirements for combining additional sources of ITS data in Texas.
SwRI divided implementation of the infrastructure into phases so that successes as well as needed changes could be recognized early in the project. The initial focus was connecting Texas Department of Transportation centers, but that project has evolved into connecting transportation centers representing various agencies such as police, transit and others. Phase 1 implements roadway status information, traffic speed, incidents and lane closures. Phase 2 adds device command and control, dynamic message signs, lane control signals, closed circuit television and video switching. Phase 3 provides support for data that cross the multi-modal boundaries between agencies. This includes support for data such as environmental sensors, transit data, parking lot data, high occupancy vehicle (HOV) lanes and traffic signals. As different levels of functionality are developed, they are being deployed across centers throughout the state of Texas.
Core Infrastructure and Building Blocks
Many of the intelligent transportation systems to be interconnected were built before there were ITS national standards. As a result, a software infrastructure had to be developed that allowed legacy systems to communicate using the evolving ITS standards. The Institute is helping develop and establish many of the center-to-center ITS standards. As new systems are developed and deployed, they will use the national standards so the systems will be more easily integrated into the infrastructure.
The center-to-center project developed a set of building blocks to represent the mechanism to interconnect dissimilar traffic management systems. The building blocks include reusable software and hiding the details of the ITS national architecture implementation from a traffic management center. This approach was taken because, in most cases, center-to-center will be used by legacy systems that are not compliant with the ITS national architecture. Legacy systems communicate using a protocol specified in an interface control document. The building blocks were developed in Phases 1 and 2. Among these is a data provider that receives data from an ITS system in interface control document format, converts the data to Traffic Management Data Dictionary format and then transmits it to other blocks. A data collector building block receives traveler information data (such as speed, incident reports and lane closures) from multiple sources in Traffic Management Data Dictionary format and stores the data. The data extractor can receive data from the data collector block or a data provider block in Traffic Management Data Dictionary format and convert it to Interface Control Document format. The command and control sender interfaces to an ITS to transmit command and control requests for ITS equipment while the command and control receiver interfaces to a traffic management system to receive command and control requests for equipment.
When the concept of command and control was introduced to the center-to-center infrastructure, the team noticed that no two centers implement security in the same fashion. The differences in approach did not allow the center-to-center project to implement a security model, so the implementation of system-specific security was left to the command and control receiver. Center-to-center transmits a username and password with command and control requests but makes no attempt to validate the username and password combination this approach allows the receiving system to use the existing security model to validate the request.
The center-to-center concept is based on the idea that not all traffic centers are the same. Each traffic center will have different equipment and operational scenarios, and therefore will participate uniquely in the center-to-center infrastructure. The building block concept developed allows traffic management centers to choose the data they want to deposit into the infrastructure and the type of command and control requests they will allow their operators to issue and their TMC to receive.
Because the building blocks for Phases 1 and 2 used an evolving standard known as DATEX (Data Exchange), performance of the connections between blocks was a concern. A significant amount of performance testing and tuning helped assure that the center-to-center infrastructure was scaleable and that data throughput would not be compromised. The Phase 3 development efforts are migrating all of the data exchange to use XML/SOAP (eXtensible Markup Language/Simple Object Access Protocol). The interface to the infrastructure will also be available using XML.
The initial center-to-center deployment involved the interconnection of the state-operated traffic management centers in Dallas and Fort Worth. These centers, built before national standards were established, had been operated as separate entities. Once the center-to-center infrastructure demonstrated that the operational requirements were being met, the deployment was extended to include the San Antonio TransGuide® system. An effort is currently under way in Austin to connect the City of Austin police computer-aided dispatch system to the state-operated transportation management center. The long-term vision is to include all of the major centers in Texas including Houston, El Paso and Amarillo, along with various regional areas such as Mexican border cities and the I-40 corridor across the Texas panhandle. This will allow the status of major interstate transportation corridors such as I-10, I-35, I-20 and I-40 to be viewed from a common point.
Additional deployment efforts in the Dallas and Fort Worth area will interconnect many local agencies such as the City of Fort Worth and the City of Dallas into the center-to-center complex. This deployment will include agencies such as local transit centers and traffic signal systems.
Agencies that have no formal automated centers also need a
mechanism to deposit and retrieve information from the center-to-center
infrastructure. Many of these centers record data on lane closures and traffic
incidents but cannot report them for collection at the regional level. A
browser-based application was developed that allows the entry of incidents, lane
closures, device commands and status information.
For center-to-center to succeed, it must be highly extensible so that additional functionality can be seamlessly added, and participants in the infrastructure do not need to continually upgrade their software. Within the next year, the following functionality is expected to be added to the center-to-center infrastructure: additional device support, ramp meter, HOV lanes, traffic signals, environmental sensors, railroad crossings, highway advisory radio, parking lots, school zones, rail stop locations, bus stop locations, reversible lanes, dynamic lanes and vehicle priority.
With respect to software upgrade, communications within the system are "tagged" with version numbers so that sending and receiving applications can be implemented to handle multiple versions. While this approach can increase the complexity of the code base, it was done so that agencies are not required to upgrade their software each time a modification, no matter how small, is made to the infrastructure.
National Architecture Issues
The development of the center-to-center infrastructure was based on ITS national standards. In particular, the data elements and message sets from the Traffic Management Data Dictionary Steering Committee were used as the basis for the implementation. After Phase 2, the development team estimated that 98 percent of the data elements deployed were consistent with those defined in the Traffic Management Data Dictionary and other related criteria, but only about 50 percent of the messages were consistent with those defined in the dictionary's Message Sets for External Traffic Management Centers Communications.
The reason for the 50 percent message-set compliance is that the message sets were overly demanding with regard to how much data needed to be transmitted, and they did not support a device command and control concept that was consistent with how TMCs perform these operations. In response to this, the development team carefully modified the standard and documented all changes to the standard development organizations.
One of the goals of this project was to evaluate the maturity of the ITS standards for deployment, so the project team provided significant input back to the standard development organizations for lessons learned to be included in future revisions. The Traffic Management Data Dictionary Steering Committee is overseeing a modification effort that will update these standards based on the lessons learned from this project. Once this is complete, the actual implementation is expected to be close to 90 percent consistent with the standards.
Southwest Research Institute is participating in and chairing several committees for national traffic system standards to help create a centralized infrastructure to benefit travelers. An extensible and flexible center-to-center system can be implemented using ITS national standards. Owners and operators of TMCs are also becoming aware of the need to share information between centers, and the technique described in this article exhibits this exchange.
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Published in the Summer 2003 issue of Technology Today®, published by Southwest Research Institute. For more information, contact Joe Fohn.