An effort was initiated in 2007 to update the “Road Weather Information System Environmental Sensor Station Siting Guide”, originally published by FHWA in 2004 (FHWA-HOP-05-026). The results of this work are documented in the report “Implementation and Evaluation of RWIS ESS Siting Guide”, produced for FHWA by Mixon-Hill and Cambridge Systematics, and issued in July 2008. A stakeholder process was conducted in order to document experience with implementation of the ESS Siting Guidelines. An initial phone outreach was conducted to nine DOTs. Most of these agencies have extensive RWIS, although most of the systems were implemented prior to issuance of the Guidelines. Three states; Michigan, New Hampshire and Idaho, were selected for site visits and in-depth interviews. The suggested revisions to the Guidelines are based on input from both phases of the stakeholder process.
Those familiar with the Guidelines generally provided positive feedback. The consensus was that the Guidelines covered most of the major issues in the siting of ESS and provided the necessary information in a concise manner. Knowing that there would be a number of recommended additions to the Guide, one important objective identified early in the process was to maintain the Guidelines as a concise and accessible document that stayed focused on the deployment of ESS. Suggested modifications and their disposition is discussed briefly below:
Accepted modifications
- Recommendations were made to cover some additional areas of interest related to ESS deployment including archaeological constraints, soil conditions, and clear zones. One respondent noted that a site had been impacted due to archaeological considerations. References were added in the report in Section 5.4 to alert users that environmental and archaeological review of sites should be conducted to identify any potential impediments to implementation. This section also noted that siting must be subject to safety clear zones.
- The report was revised to note the influence of soil mechanics on ESS siting and recommended the use of the EPA “National Pollutant Discharge Elimination System (NPDES) Stormwater Guide” to evaluate issues related to stormwater runoff. This reference was added in two sections of the report.
- A number of respondents asked that more examples be provided of the tradeoffs required in siting ESS. Two good examples of siting tradeoffs were noted by New Hampshire DOT and included in ther report. Both cases illustrated the tradeoffs that must often be considered between infrastructure availability, right-of-way and meterological concerns.
- Several additions were made to the Guidelines to emphasize the importance of ongoing maintenance. Site access and accessibility to major components of the ESS should be considered in order to reduce maintenance costs over the long term.
- Major changes were made to the metadata table that was included in the original report. Since the original Guidelines were developed a major effort was conducted as part of the Clarus project to define an standard set of metadata for ESS. An expanded metadata table was thus included in the Guidelines showing Clarus metadata in three categories; required, recommended and optional. The metadata requirements defined for Clarus were quite extensive and may not be realistic for all ESS installations. Some items in the recommended and optional categories were highlighted as not being critical for most DOT requirements.
Summary
Overall a very limited number of changes were recommended for the guidelines document. Other than the modification to the metadata table, most of the additions were limited, and designed to highlight areas of concern noted by DOT’s with ESS experience. It is the case that many agencies are deploying other ITS technologies with ESS; however it was felt that this could greatly expand the document and result in a loss of focus on ESS technology. The feedback from most of the DOT’s interviewed was positive and they expressed an interest in using the document for future deployments. Several noted that they would require their contractors to use it as part of their design efforts, as the Michigan DOT is currently doing.
FHWA currently tracks ESS deployment throughout the U.S. on a regular basis. This effort should be expanded to obtain information on whether the Guidelines are being used. Agencies that are using them could be asked for feedback on their effectiveness. This will enable FHWA to obtain continuous feedback and based on that feedback, determine when any future revisions are needed.
