4.0 State DOT Implementation Experience and Evaluation

This section discusses State DOT experiences in implementing and evaluating the Guide as part of recent or new ESS deployments.

4.1 Michigan Department of Transportation Implementation and Evaluation

4.1.1 Background

In 2006, the Michigan DOT (MDOT) began to plan the deployment of RWISs and ESSs across all regions of the state. While the Department has previously supported aeronautical weather stations across the state, this plan is the first effort focused on road weather information collection by MDOT. The plan is a significant component of MDOT’s ITS Strategic Plan, and is coordinated with the ITS regional architecture and statewide ITS deployment plans.

MDOT decided that its initial RWIS program deployments would be in its Superior Region. The effort was segmented into several projects, the first of which was to study road weather information needs and opportunities, to be documented in a Concept of Operations (COO). That project was followed by the detailed design studies, which resulted in a set of design and procurement documents. Construction of the first set of ESS sites and RWIS implementation is planned for completion in 2008.

The MDOT development timeline has coincided with this review of the ESS Guide and has allowed participation in many of the MDOT RWIS program milestone meetings. While it is not the intent of this report to reproduce or redistribute the MDOT project documentation, it was helpful to the analysis to have direct access to MDOT and its contractor personnel. Meetings attended in conjunction with the MDOT project included:

• RWIS Project Deliverables Review, April 10, 2007 – Reviewed analysis of user needs and draft Concept of Operations for RWIS/ESS in Michigan’s Superior District (Upper Peninsula)
• Design Project Kickoff Meeting, Sept. 10, 2007 – Kickoff meeting for final site selection and site design pursuant to developing bid packages for build-out
• Design Project Progress Meeting, Nov. 6, 2007 – Update on progress of site surveys, plans, and geotechnical analysis in preparation for preliminary design submittal
• Design Project Preliminary Design Review Meeting, Dec. 13, 2007 – Preliminary design review of ESS site design, RWIS, and associated DMS
• Design Review Meeting, March 5, 2008 – Final design review for all components of the project; distribution of bid package documents for review

4.1.2 Experience Relative to the Guide

4.1.2.1 Requirements Assessment

The requirements assessment for MDOT’s Superior Region RWIS deployment was performed in the first study project and documented in the COO as described in Section 4.1.1. Requirements in the COO addressed user needs, ESS siting, sensors and devices, and communications/power/processing. These categories broadly match the content of the requirements Section 2.0 of the Guide.

Section 4 of the COO documents the RWIS User Requirements from the perspective of each of several stakeholder groups, including operators, system administrators, maintenance technicians, trainees, DOT management, media, public/private partners, and road maintenance services. This is similar in concept to the discussion of functional applications in the introductory text of the Guide Section 2.0. These user perspectives provide detailed interface requirements for each stakeholder group, but provide relatively few functional requirements.

Section 5 of the COO begins with a reference to the FHWA Guide Section 2.2 and the discussion of “local” and “regional” siting issues. It also notes that “the approach selected during the stakeholder process is a combination of these,” driven by the need to get data for particular “trouble spots” while retaining the flexibility to apply the data regionally. This is to be accomplished by deploying a full complement of sensors at each station and by locating and designing each site to serve both types of applications. This section also discusses MDOT’s interest in locating the ESS sites near other state facilities so as to reduce the cost of utility connections. The section concludes with a list of proposed locations.

Section 6 of the COO corresponds to Section 2.1 of the Guide and discusses environmental sensors and devices. The applications of road weather information are discussed as an introduction to the sensors that provide the underlying data. Station sensor configurations are then presented for “basic” and “reduced power” installations, and for optional sensors applicable to those configurations. Special case configurations for seasonal flooding and portable ESSs are also discussed.

4.1.2.2 Site Selection

Site selection for the Superior Region has been ongoing throughout the project. Sites were initially nominated by stakeholders and consolidated into a list of thirty-three candidate sites. These sites were, for the most part, initially selected based on attributes that would categorize them as “local” ESS sites—historically heavy local snow, or high winds and blowing sand, or severe icing. Some sites, however, were suggested specifically because weather monitoring in the area was particularly limited and there was a need for a “regional site.”

Based on the studies documented in the COO and MDOT’s program budgeting, the list of sites was reduced to six high-priority locations to be deployed in conjunction with five dynamic message signs (DMSs). MDOT’s desire to integrate RWIS and ESS deployment was a significant consideration in all site selection discussions and provides an immediate and public demonstration of the value of RWISs and ESSs.

Site selection was further refined in the RWIS design phase. Discussion in the design project kick-off meeting led to a relocation within the general vicinity of two of the six sites. It was further noted in the meeting that sites along the M-28 corridor had not been fully evaluated with respect to the Guide in prior phases and should be further evaluated to provide optimal siting. Site selection was finalized in the Preliminary Design Report, specifically noting that criteria in the Guide provided the basis for siting.

4.1.2.3 Recommended Siting Criteria

The Preliminary Design Report describes the siting and sensor requirements specific to each of the six selected ESS locations and explicitly references the Guide as a basis for the design of each site.

“In general each specific sensor has its very own unique set of requirements which must be met, such as mounting placement height on tower, to enable optimal ESS site operation. However each RWIS ESS site location as a whole also has some very high-level requirements and guidelines, as defined by the FHWA. Generally the major guidelines applicable to this deployment phase are:

• Distance from edge of pavement (maintaining minimum distance/clearance of 30 feet from the edge of pavement).
• Openness of site location (eliminating site locations near a hill, trees, body of water, bridges, etc.). Typically ESS sites must be about 10 times (the size of the nearest obstruction) farther than obstructions.

All RWIS ESS sites in this Bid package were selected and further defined following the FHWA Guide, and are located in open areas for better representation of the local weather elements while minimizing weather data measurement bias.”

Site locations and ESS design specifications are assembled into procurement packages for bidding. Consistent with MDOT’s standard practices, the relevant ESS specifications have been compiled into a Special Provision for Environmental Sensor Station (Special Provision).

Table 1 – Guide Siting Criteria and MDOT Implementation

Guideline Topic	Relevant Text  from Guide	Discussion	Exception to Guidelines?
Tower Design	“The tower should be sturdy (e.g., open matrix type) using instrument booms to reduce contamination of sensor data by turbulence and wind flow around the tower structure. For water level and road flooding applications, standpipes (i.e., vertical pipes ranging from 3 to 12 inches in diameter and up to 10 feet tall such as shown in Figure 5) are typically used. Masts can be placed above the top of the standpipe to mount wind, air temperature/dewpoint, or other weather sensors. In this situation, the weather sensors may not be consistent with the siting guidelines below; however, the sensors should be installed high enough above the top of the standpipe to eliminate the environmental effect caused by the standpipe.”	Tower design is specified in the Special Provision and is consistent with this description. Water level and road flooding applications are not applicable to any of the sites.	N
Distance of Tower from Roadway	“At this time, there are no studies that determine the minimum distance the tower should be placed from the roadway to avoid the effects of traffic on the accuracy of the sensors (e.g., heat, wind, splash) or how close it must be to adequately represent the environment over the roadway. Towers are most frequently installed within a range of 30-50 feet (9-15 meters) from the edge of the paved surface.”	Distance from pavement ranges from 34 to 51 feet.	N
Pad and Barrier	“The tower base should be attached to a concrete pad to provide a sturdy platform. The size of the pad should take into consideration the soil conditions, frost activity, and wind loading. If the tower is within the clear zone, a barrier or guard rail should be used.”	Concrete pad is specified in the Special Provision and is consistent with this description. None of these sites are within the clear zone.	N
Tower Base Elevation	“The tower base should be at the same elevation as the surface of the road, if possible.”	Elevation offsets are not noted in the Special Provision or plans. All sites are located on level ground near roadways.	N
Tower Height	“The tower height should depend on the planned sensors. If a wind sensor is planned, the tower should be tall enough to install it at a height of 33 feet (10 meters).”	Per the Special Provision, the tower height will be according to the manufacturer’s requirements, but not less than 30 feet. This is not necessarily a deviation from the Guide, since the wind sensor could be on a three-foot boom.	N
Site Terrain	“Towers should be sited on relatively flat terrain. If possible, avoid steep slopes within 300 feet (approximately 90 meters) that could impact wind measurements.  Sites near steep road cuts, swampy areas, and bedrock (a detriment to cable trenching) should be avoided.”	All sites are on relatively flat terrain. Sites near open water are intentionally so located for monitoring local conditions.	N
Tower Wind Shadow	“If possible, towers should be placed upwind of the roadway based on the predominant wind direction for the season of most interest.	Predominant wind directions are not explicitly noted in the design documentation, but all sites are described as being representative of local conditions.	N
Surrounding Terrain Coverage	“The surrounding terrain coverage out to at least 50 feet (15 meters) should be low vegetation or native soil.”	The exact nature of coverage and distance to tree lines are not indicated on plan sheets.	N
Standing Water	“Avoid standing water. Many ESSs are installed on the opposite side of a depression adjacent to the road. This depression is a natural collection point for rain and/or water draining off the road. Given the choice of two potential sites, both of which would satisfy other siting requirements, the ESS should be installed in the one less likely to be affected by ponding water.”	Several sites are indeed near drainage ditches, but there are no indications of extended periods of ponding.	N
Site Fence	“A fence should cordon off the tower from its surroundings if the threat of vandalism is present. If possible, the distance between the fence and the tower should be at least 15 feet (5 meters). This distance is recommended to minimize the effect of the fence on the sensors readings especially when weeds and/or debris on the fence act as a horizontal obstruction. Limited space in the right of way may require the distance between the fence and tower to be reduced. The positioning of the fence and its gate should not restrict access to the equipment or the tower. Careful planning is necessary to assure that fold-over towers with their attached instrumentation may be lowered with sufficient room for a technician to work on the sensors.  The fence should not obstruct any sensors on the tower.”	The Special Provision specifies the design of the fence and gate. Sites are specified to be as small as ten feet by ten feet. The gate is to be designed so as to allow access to both sides of the tower when it is lowered through the open gate.	Y
Unauthorized Access	“Anti-climb panels can be installed to restrict persons from climbing up the open lattice of towers.”	Anti-climb panels are not specified in the Special Provision, but access is limited by the site fence. The top of the fence is specified to include materials intended to prevent unauthorized entry, meeting the intent of the guideline.	N
Maintenance Access	“Ease of maintenance tasks should be considered in the siting, such as the use of folding towers and the availability of maintenance vehicle pull offs.  In some situations, sensor heights may need to be adjusted to accommodate maintenance activities.”	Folding towers are specified in the Special Provision. Vehicle access was evaluated and noted for all sites.	N
Alternatives to an ESS Tower	“Insufficient space in the right-of-way outside the clear zone may preclude installation of a tower. If requirements for road weather information preclude selecting another site, DOTs may find other options for installing some atmospheric sensors.”	The guideline is not applicable. All sites are designed with the tower described in the Special Provision.	N
Site Metadata	“The positioning of the tower and the height of the sensors on the tower should be included in the metadata file available for the data customers.”	Metadata meeting this guideline are required in the Special Provision.	N
Sensor Locations	Sensor location guidelines are detailed throughout Section 4.2 of the Guide.	The Special Provision specifies that all ESS instruments and devices shall be installed in accordance with manufacturer guidelines. It furthermore specifies that the contractor shall comply with the latest edition of the Guide.	N

4.1.2.4 Additional Considerations

Significant attention was given throughout the planning process to the non-meteorological aspects of the Superior Region ESS deployment. Power and communications issues are addressed with their own Special Provisions within the bid package. Aesthetics were explicitly considered in Section 5.0 of the Preliminary Design Report and are being addressed in a manner consistent with the Guide. Security and access are addressed by sites designed specifically to conserve the site footprint, fencing, and access constraints by using a “folding” tower design that lowers the tower and instruments through the gate opening in the site fence.

Siting metadata is not yet available for the Superior Region deployment, but requirements for the provision of metadata by contractors have been included in the Special Provisions. Metadata is to be provided and, at a minimum, include all items listed in the most recent version of the Guide.

4.1.3 Conclusions and Recommendations

The MDOT Superior Region RWIS/ESS program has made extensive and profitable use of the Guide. The Guide was consulted at key milestones throughout the program thus far and has provided a base body of knowledge for much of the system documentation.

Integration with other ITS components—in this case, message signs—is an important aspect of the Superior Region deployment that is not, however, detailed in the current Guide. The inclusion and evaluation of these components as part of the road weather information requirements can impact, for example, site location and the specification of particular sensors to support the desired messaging.

The only significant deviation from the guidelines in the MDOT design was the size of the fenced enclosure for the ESS. The Guide recommends fifteen feet between the ESS tower and the fence, whereas the MDOT Special Provision for ESS specifies a ten feet square enclosure for the commercially-powered site—five feet between the tower and the fence. The Guide bases its recommendation on the need to preclude the enclosure from affecting sensor measurements, but MDOT has placed other specifications on sensor accuracy that will force the contractor, ESS manufacturer, and maintenance provider to make allowances for the smaller enclosure.

It has also come to light in the Superior Region ESS deployment that the siting criteria within the Guide need to be updated to reflect advances in sensor design. Many of the recommendations in the Guide (for example, the sensor locations in Section 4.2) were developed for older-model sensors and may be inappropriate for the newer equipment. In practice, MDOT specified sensor performance criteria in its Special Provision for ESS and required the deploying contractor to both comply with the Guide and to install and calibrate the ESS according to the manufacturer’s guidance. It is recommended that the Guide suggest in Section 4.2 that agencies and their contractors follow the manufacturer’s guidance for installation and calibration of all sensors, relying on the subsequent guidance only in the absence of more specific instructions from manufacturers.

4.2 Idaho Transportation Department (ITD) Evaluation

4.2.1 Background

ITD has operated RWISs throughout the state of Idaho since the late 1980s. Data provided by the system has been useful to both ITD maintenance staff and travelers throughout the state. Information in the form of observation data and camera images is available to the staff through the Road-Weather Integrated Data System (RWIDS) and to the travelers on the ITD website.

ITD contracted with Iteris in 2005 to assist with the planning, site development, site assessment, and procurement for its Statewide RWIS Build Out project. As described in the Site Assessment Report, the project developed an implementation approach for deployment of a significant number of RWIS ESSs over several years, developed the basis for subsequent plans and specifications, and provided an assessment of build out priorities from among the potential ESS sites. FHWA’s Guide was used by both ITD and Iteris in this project. The report concluded with recommendations for deployment over a multi-year period.

ITD’s prime contractor, Vaisala, is providing the ESS packages and calibration services during the construction phase, with site installation being provided by an Idaho-based civil engineering contractor. The first of these new sites was deployed in 2007.

Most of the original ESS sites need upgrades to make the ESS messages comply with NTCIP 1204. ITD has contracted to make these upgrades.

ITD has considered creating an algorithm that would automatically present a message recommendation to an operator for DMSs. The DMSs in Idaho are operated by other state and local agencies, however, and not by ITD.

ITD is currently not considering using ESS information for their 511® system. ITD believes that the trend for 511 is going away from presenting weather information except for alerts and warnings received from the National Weather Service.

4.2.2 Experience Relative to the Guide

4.2.2.1 Requirements Assessment

The Site Assessment Report describes in detail the ITD stakeholders involved during the planning phase. Two decision points for site placement were money and number of sites in each district. Based on the number of sites, stakeholders looked for trouble spots and areas that would represent a large segment of roadway suitable for an ESS site. Factors that were found to be important in site assessment and prioritization include the following:

• Maintenance Support Characteristics
• Weather Characteristics
• Road Characteristics
• Logistical Characteristics
• Other Functional Characteristics

4.2.2.1.1 Maintenance Support Characteristics

Because of their knowledge of local weather and their experience with maintenance, the input received from ITD District personnel, maintenance foremen, and lead workers was the primary input used in the prioritization of the ESS sites. These stakeholders are often called on to drive out into their areas of responsibility to assess road weather conditions. This practice provides first-hand knowledge of the situation, but may incur increased risk, time, and expenses in labor and fuel. RWIS deployments that address the need for timely and operations-critical information can mitigate these costs and risks.

These advantages can be further leveraged by considering the use of a single site to provide observations that may be characteristic of more than one roadway or maintenance area. Sites that could be used for multiple roadways or maintenance needs should receive higher priority in deployment decisions.

4.2.2.1.2 Weather Characteristics

While the Guide draws a distinction between regional and local sites, the variation in Idaho’s topography, like that of other mountainous states, calls for ESS sites with widely varying areas of application. A site may be typical of a long highway segment along the base of a range, but have very different conditions than within an adjacent canyon. ITD chose to give higher priority to sites that are representative of conditions over larger areas or longer roadway segments.

Some ITD maintenance personnel indicated that they may use data from the existing RWIS ESS as a forecasting tool for conditions downstream of the weather event. In the absence of better forecasting tools, sites where personnel suggested that this might be helpful were given higher priorities.

4.2.2.1.3 Road Characteristics

ESS sites along roadways with higher functional and winter maintenance classifications were given higher priority by ITD than those with lower classifications. This prioritization reflects the usefulness of RWISs in providing information that improves winter maintenance and traveler information on more heavily traveled routes.

4.2.2.1.4 Logistical Characteristics

Provision of services for successful RWIS ESS operations was a consideration for ITD in siting. Siting decisions balanced optimal ESS placement with cost increases, and did not take exception to guidelines or affect siting priorities. Logistical factors considered by ITD included access for construction and maintenance, right-of-way ownership, power, and communications. Alternative locations or services were evaluated for cases where the preferred or standard configuration was not viable. For example, a site without commercial power access was evaluated with solar power.

4.2.2.1.5 Other Functional Characteristics

ITD site assessments included consideration of existing and planned ESSs not associated with ITD or road weather systems. Proposed ITD sites that were near existing ESSs were evaluated to determine whether maintenance information needs could be fulfilled by the existing sites. If those needs could be fulfilled by enhancing the existing site, the proposed new ESS was given a lower priority.

Site assessments also considered proximity of other ITS field elements with which ESSs could share power and communications, or with which there might be additional information advantages. ESS sites downstream of DMSs, for example, provide notification of weather conditions to allow travelers to find alternative routes.

4.2.2.2 Site Selection

A comprehensive RWIS Location Data Collection Checklist was developed by ITD from the Guide. The checklist was used at each location to document the characteristics of the location, function, purpose, observations desired, physical description, site metadata, sensor considerations, and other considerations such as aesthetics, right-of-way issues, existing or planned improvements, and security concerns. Several fields were provided for miscellaneous comments. Development of the checklists confirmed that the purpose of most of the sites was for maintenance, with traveler information being a distant second, and that the function of the sites was predominantly local. In addition to the checklist, sketches and photos were taken of each site and the surrounding area.

The Site Assessment Report was largely composed of these checklists. In the report, ITD did an excellent job of documenting the processes and results of their site investigations and assessment. The report includes a comprehensive summary of the sites, providing the estimated cost and installation year for each site. In support of this analysis, ITD gave descriptions by district of each site being considered and the intended siting criteria.

4.2.2.3 Recommended Siting Criteria

ITD ESS siting criteria have been directed primarily at supporting highway winter maintenance. Within the maintenance context, supporting capabilities, such as providing information for pavement temperature forecasts, were considered on a case-by-case basis. The detailed Site Assessment Report results for each potential site configuration were evaluated for types of sensors, cameras, power and communication services, and installation and maintenance.
Standard atmospheric sensors considered in the report include:

• Air Temperature
• Relative Humidity
• Precipitation (Y/N)
• Wind Speed and Direction
• Barometric Pressure

“Special” sensors in the context of the Site Assessment Report are characterized by increased cost and technical complexity beyond that of the standard atmospheric sensors. Such sensors include:

• Present Weather Sensors
• Precipitation Type and Rate
• Visibility
  • Solar Radiation
  • Sub-Grade Moisture and Temperature
  • Others

Pavement sensors, where desired, were assumed for site evaluation purposes to be in-pavement pucks providing information such as temperature, chemical composition, moisture, and freeze point. ITD would like guidance on selection of sensors to support particular applications to be included in the Guide.

Traditional utility-based power was preferred at all sites. In those cases where access to utility power service was limited, other options were evaluated for consistent installation and maintenance cost bases.

Telephone landlines were the preferred means of communications between the RWIS ESS and central system servers. In those cases where access to landline service was limited, cellular and radio services were evaluated for consistent installation and maintenance cost bases.

Cameras were included in each site assessment, distinguishing only between use of fixed versus pan-tilt-zoom (PTZ) models. The intended direction of view for the cameras and the need for street lighting were noted, if appropriate. ITD would like guidance on selection of cameras to support particular applications to be included in the Guide.

Installation features in the base siting criteria included a simple foundation, fold-over tower, and fencing, with notations for significant grading or clearing requirements.

4.2.2.4 Additional Considerations

There were several challenges during right-of-way negotiations, one of which proved to be especially difficult. Due to the large amount of federal land in Idaho, each county and/or division is responsible for negotiations and has its own unique rules.

The selected contractor and ITD differed on their interpretations of the Request for Proposal (RFP ) regarding designing and building tasks for the ESS deployment. Due to the differing interpretations, negotiations took longer than expected. If possible, ITD would like guidance on ESS deployment proposal and procurement requests added to the Guide, or another set of guidelines produced for this purpose.

A site had to be placed in a different location due to archaeological evidence of ancient human migration. More information in the Guide would be helpful.

Soil evaluation was not specifically done at each site. ITD ran into some problems with lava rock and had to spend more money during construction. More information in the Guide would be helpful.

Roadside safety clear zones were not specified in the RFP. A change order was required to address this issue and caused a delay in the project. More information in the Guide would be helpful.

A reference to the National Pollutant Discharge Elimination System (NPDES) Stormwater Guide should be provided in the Section 4.1 of the Guide (relative to the discussion of standing water) for stormwater management at sites. (The Stormwater Guide is available at http://www.epa.gov/npdes/pubs/sw_swppp_guide.pdf.)

Coordinating the construction of a site with the installation of power and communications was a major challenge. Documenting risks and assumptions associated with these services in a Project Management Plan is important in managing deployment activities. A reminder to address these factors early in the deployment process would be helpful in Section 5 of the Guide.

With the rising cost of fuel for generated power, the decreased amount of sun for solar panels, and the security issues with publishing power line locations, selecting the correct power source for each site was another challenge. Another consideration was the amount of snow, up to 15 feet, that might accumulate at the site that could affect the power. Section 5.2 of the Guide should address the potential impact of weather conditions on availability of power source alternatives.
Communication between the remote processing unit (RPU) and the server was the most difficult challenge. Wherever there was fiber, the choice was simple. Although cell phones are more expensive than fiber, they are the only other viable option as the amount of snow in Idaho would make using satellites very problematic. During future deployments, ITD will prioritize locations with fiber communications.

4.2.3 Conclusions and Recommendations

In summary, ITD suggests the following additions to the Guide as discussed elsewhere in this section:

• Guidance on selection of cameras to support particular applications
• Guidance on selection of sensors to support particular applications
• Guidance on creating RFPs for ESS deployment
• Guidance on archaeological impacts on siting (“ancient migrations”)
• Guidance on soil evaluations
• Guidance on roadway clear zones
• Reference to the NPDES Stormwater Guide

Throughout this process, ITD has learned that deploying an RWIS system is hard work. They have also learned that communications and power issues need to be determined early in the project.

4.3 New Hampshire Department of Transportation Evaluation

4.3.1 Background

New Hampshire’s RWIS program was developed primarily to address traveler information and winter maintenance needs in a state that can experience severe winter weather any time between October and April. It was financially important to the state   to optimize allocation of maintenance resources, including chemical applications, during winter. New Hampshire DOT (NHDOT) also saw an opportunity to include weather considerations in work planning during construction season. Areas of traveler information support include identification of adverse weather conditions, issuance of traveler advisories, pavement forecasts for specific roadway segments, and dissemination of data to other government agencies and educational institutions.

The RWIS program was a development from the Tri-State Rural Advanced Traveler Information System (TRIO), a Multi-State ITS project carried out jointly by New Hampshire, Maine, and Vermont. NHDOT deployed a pilot ESS on the Little Bay Bridge in Newington, NH in 1997 and then initiated plans for a larger, statewide system.

The deployment of 12 ESSs in New Hampshire in 2005-2006 represented a successful collaboration of a number of groups, including NHDOT divisions and outside agencies. Highway design, highway maintenance, materials and research, and the Bureau of Environment all participated from within NHDOT. FHWA and the Highway Patrol also provided support and Plymouth State University (PSU) served as the DOT’s meteorological consultant. One of the PSU staff members visited potential sites with NHDOT. ESS locations are shown in Figure 1. Most of the ESSs were sited to be representative of meteorological conditions over a wide area. There was also a focus on serving the heavily traveled I-93 corridor, New Hampshire’s main north-south highway. The stretch of I-93 between the Massachusetts State Line and Manchester, NH is a major commuter artery with some of the highest traffic volumes in the State. I-93 also serves as a major recreational route. Keeping this route open to the winter recreational areas in the Lakes Region and the White Mountains is very important to New Hampshire’s economy.

Figure 1 – New Hampshire ESS Sites

Source: New Hampshire DOT.

4.3.2 Experience Relative to the Guide

4.3.2.1 Requirements Assessment

NHDOT recognizes that siting of ESSs is a balancing act with multiple objectives. Their goal is to obtain representative data for forecasting and resource deployment decisions, while also serving specific trouble spots that are remote from maintenance facilities. The Guide was not complete at the time that NHDOT sited its ESSs. NHDOT’s Project Manager attended a seminar on ESS siting at their vendor’s headquarters. He obtained a site survey checklist that he used in the process and filled out for each prospective site.

4.3.2.1.1 Maintenance Support Characteristics

Local NHDOT maintenance personnel were consulted during the siting process and their knowledge of roadway characteristics was considered by NHDOT headquarters personnel to be very helpful. NHDOT also wanted to involve local maintenance supervisors as a way of educating them about RWISs and future maintenance requirements. The primary users of RWISs are winter maintenance personnel. Summer maintenance and construction personnel are likely to take advantage of the information as well.

NHDOT currently has a maintenance contract providing access to remote diagnostics over the phone, reducing the costs for NHDOT. Some basic preventive maintenance such as camera lens cleaning is done by NHDOT and they are starting to train some of the maintenance personnel in the signal/traffic bureau to service electronics as well.

Maintenance personnel also played a key role in the deployment of first-phase ESSs. NHDOT bridge maintenance personnel ended up pouring all of the concrete pads for the ESSs since they could do it much less expensively than the vendors. Coordination was important to make sure that mechanical and electrical connections were compatible with the vendors’ designs. While the Guide does not need to address these types of design issues in detail, identification of these issues and some high level guidance would be helpful.

4.3.2.1.2 Weather Characteristics

NHDOT’s ESSs include sensors that provide wind speed and direction, humidity, pressure, air temperature, dewpoint temperature and visibility. An ultrasonic anemometer was selected for inclusion for enhanced reliability. Precipitation sensors differentiate between rain, snow, and drizzle and measure actual precipitation rates as water accumulation. A minimum of two pavement sensors and one subsurface sensor at 47cm depth are included at each ESS station. Ozone sensors were provided as part of a cooperative agreement with Plymouth State University. Roadway sensors provide pavement temperature, freeze point temperature, and chemical concentration data. NHDOT has found the pavement sensors to be very reliable. Traffic count data are also collected at ESSs.

NHDOT has found that no product performs all tasks well. Some products are stronger in some areas and weaker in others. Agencies have to understand their priorities and look for combinations that best meet their needs. A better understanding is needed of active and passive sensors, and the tradeoffs involved.

4.3.2.1.3 Road Characteristics

The NHDOT RWIS program is focused on the Interstate system and major trunk highways. The limited-access highway system does not extend, however, to the southwest and far northern portions of the state. As a result, tradeoffs need to be made between the need to represent statewide meteorological conditions, service the largest number of users, and address critical locations in the system.

4.3.2.1.4 Logistical Characteristics

Power, communications, available real estate, and easy access were also considered as primary siting requirements. Power availability was an absolute requirement and was not a problem at most sites. NHDOT generally sited ESSs on its own property, with several of them located at rest areas or maintenance sheds. They avoided using easement rights of way but this may be an option in the future.

One of the goals of NHDOT in siting ESSs is to reduce recurring costs, of which communications is a major component. Vendors bidding on the initial deployment had to provide a communications plan for each site. Two sites have direct access to NHDOT facilities while most others use cell phones for communication. One site, Franconia Notch, does not have cell phone coverage and uses satellite communication. In siting future ESSs, NHDOT will try to avoid satellite communications since this costs $50 to $60 per month compared to only $15 to $18 per month for cell phone coverage. Stations generally report at 15 minute intervals although they are polled more frequently.

4.3.2.2 Site Selection

Most of the initial ESSs deployed were sited to be representative of meteorological conditions over a wide area. There was also a focus on serving the heavily traveled I-93 corridor, New Hampshire’s main north-south highway. Two locations were selected to address specific, localized problems. One is located along Route 9 in Chesterfield in southwest New Hampshire. The ESS is located on top of a hill above the Connecticut River Valley where a combination of heavy truck traffic and wet, icy conditions can create safety problems. The other spot location is along Route 112 at Lost River in northwestern New Hampshire. This is a roadway trouble spot at high elevation and is about an hour from the nearest patrol shed.

NHDOT is generally happy with the locations selected. However, two sites have not proven to be satisfactory to NHDOT. One is located at the patrol shed along Route 101 in Manchester. This ESS is located 150 feet from the roadway in a tree-shaded area and as a result does not effectively represent the nearby roadways. One of the ESSs along I-93 was located in the median near Woodstock. This site is subject to localized air turbulence generated by traffic, which may not be representative of conditions in the general area. Adding some examples to help illustrate the limitations created by compromised siting could be a helpful addition to the Guide.

4.3.2.3 Recommended Siting Criteria

• NHDOT is planning to deploy 10 additional ESSs when funding becomes available. The Guide will be used but not applied strictly. Future deployments are being planned based primarily on geographic priorities which are listed below:
• I-93 corridor (major construction will be occurring over the next several years at the southern end of the corridor)
• A minimum of two sites per district are needed to provide information to local maintenance personnel. There are six districts.
• More ESSs are needed in the western part of the State since weather generally moves across the State from west to east.

4.3.2.4 Additional Considerations

NHDOT expects to use the ESSs to support traveler information services. Wind speed information can be used to issue warnings to trucks. They are considering linking ESSs to DMS warning signs that would be used when ice or high winds are experienced. While areas where these weather conditions may occur are generally known, siting of the ESS is critical in providing accurate indications of those conditions. One of the initial ESSs was deployed in the roadway median in a valley and is not necessarily representative of conditions facing vehicles along the roadway or in the general area.

Plymouth State University is currently looking into data quality requirements, as well as data archiving. There is currently no central repository in the DOT for weather information. NHDOT believes this would be useful for evaluating maintenance strategies and providing improved traveler information services.

NHDOT would also like to share information with other States. They are sharing information with National Weather Service through Plymouth State University and have recently made an arrangement with the Massachusetts Highway Department. There are several issues in information sharing including firewall/security within the Department and the fact that presentation formats need to be simplified in order to be useful. Personnel do not have time to interpret complex information at times of approaching severe weather when the information is most urgently needed.

4.3.3 Conclusions and Recommendations

NHDOT was not able to use the Guide in siting the initial set of ESSs but plans to use it in combination with their own criteria in the future. NHDOT believes the Guide can be helpful to address site-specific concerns; specifically the tradeoff between meteorological integrity and logistical concerns.

The following additions to the Guide are suggested as reflections of NHDOT’s experience with ESS siting:

• Guidance on selection of sensors from among alternatives measuring the same meteorological parameters
• Examples of the tradeoffs between site selection constraints and the typicality of meteorological conditions at the site