Consider the technology selected for an ITS telecommunications system carefully, as it will impact the cost and the performance of the system.
Experiences from the Departments of Transportation (DOTS) of multiple states in selecting telecommunications options.
- 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.
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.
Author: Vince Pearce
Published By: U.S. Department of Transportation, Federal Transit Administration and Federal Highway Administration
Source Date: 2000
EDL Number: 11488
Other Reference Number: FHWA-JPO-99-023/FTA-TRI-11-99-02URL: http://ntl.bts.gov/lib/jpodocs/repts_te/11488.pdf
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