Telecommunications infrastructure is important in enabling Intelligent Transportation Systems (ITS) to function, as it ties together and moves data between the major elements of an ITS, including roadside equipment, vehicles, the vehicle operator and central operations facilities (such as transportation management centers). Through integrating the individual elements of an ITS, telecommunications provides a critical technical function to the system, and can act as a mechanism for enhancing overall transportation efficiency. Telecommunications also comprises a significant share of the cost of an ITS, both in terms of implementation and operations and maintenance.
Arriving at the telecommunications solution that best suits agencies' needs is a high priority, but it can be a challenge. This is largely due to the rapid pace of change in telecommunications and the skills required to understand and assess different telecommunications alternatives. This report is designed to provide assistance on what processes work best and what factors should be considered when making telecommunications decisions. A number of the best techniques for exploring telecommunications alternatives are presented to help agencies determine the optimal alternative in support of their ITS program.
For this study, the telecommunications experiences of state Departments of Transportation (DOTs) and agencies from across the country were examined. In particular, examples of successful practices in ITS telecommunications were drawn from California, Georgia, Maryland, Michigan, Minnesota, Missouri, New York, Texas, Virginia, and Wisconsin.
When deciding on the appropriate telecommunications technology, agencies will be faced with a number of potential alternatives. A careful consideration of these alternatives is required, as the decision will have an impact on the cost as well as the performance of the system. The following set of lessons learned is offered to provide agencies with guidance in selecting the appropriate telecommunications technology.
- Develop a detailed understanding of the requirements. When making a choice, agencies must first ensure that they have a complete understanding of all aspects of their requirements and of their existing telecommunications infrastructure. This will increase the likelihood that the appropriate technology is selected.
- Evaluate each technology alternative according to a set of established evaluation factors. Stakeholders should agree on the set of factors to be used in evaluating different technology alternatives. Factors considered in decisions examined for this study included:
- Ease of interfacing with the existing ITS telecommunications infrastructure.
- Reliability of the technology.
- Ease of maintenance.
- Ability to meet current needs.
- Capacity for expansion to meet future needs (both in terms of total capacity and in terms of geographic distribution).
- Implementation costs, total life cycle costs, and available budget.
- Time needed for implementation.
- Ability of the agency to operate and maintain the eventual network, based in staffing and skills constraints.
Several examples of the factors considered by agencies and how these shaped their selection of an appropriate technology alternative include:
In the 1990s, the Michigan DOT had decided to significantly expand its Advanced Traffic Management System, at the same time as road reconstruction was occurring. Due to the reconstruction, cable based telecommunications was unattractive, as the cable might be damaged by the road work. The agency was also limited in its funding, so it decided to implement a hybrid network. The base of the network was a high capacity, fully redundant self-healing fiber optic ring. From this ring, microwave spokes extended to hub locations from which telecommunications to field devices was carried over copper cables.
In its initial design for an ATMS, the telecommunications included copper twisted pair, using repeaters to boost signals over longer portions of the network. The successful bidder for the contract, however, proposed conversion of a significant portion of the network to fiber optic cable, using a mix of multimode and single mode cabling, which would be coupled to the copper and coaxial cable connections of the field devices at telecommunications hubs. The following factors were cited in support of fiber optic over the copper twisted pair:
- The implementation would cost the same.
- The fiber optic system could be expanded more easily in capacity, length and number of connections.
- Signal quality of the fiber optic network would likely be superior to the copper network.
- The fiber optic network could be just as easily managed.
- There was less likelihood of degradation of the signal and network performance over time due to cable corrosion.
Each agency will face a different set of constraints in deciding among alternative ITS telecommunications technologies. It is critical that agencies understand these constraints, as well as the full set of requirements for their system, so that they can develop criteria, or factors, for evaluating the different technology alternatives. Through careful consideration of the alternative technologies, agencies can insure that their final selection will be cost efficient and will meet their needs.
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