Road Weather Information System
Environmental Sensor Station
Siting Guidelines
April 2005

Appendix D - ESS Checklist

This checklist is a synopsis of the siting criteria contained in the main document. The checklist provides an organized list of considerations for uniform siting of ESSs. Section numbers refer to locations in the main document.

Identify Road Weather Data Requirements and Uses (Section 2.0)

• Detect or monitor roadway conditions.
• Support winter maintenance decisions.
• Support road temperature modeling.
• Support improved weather forecasts.
• Warn travelers of road conditions.
• Help manage traffic.
• Support road construction.
• Other uses.

Identify Basic Requirement for the Site

• Regional site to provide road and weather data representative of a general area. Generally used to monitor the onset or existence of predicted conditions and to provide information used to forecast weather and road conditions. (Section 2.2)
• Local site used to detect existing or changing conditions at a specific site or to provide a predictor for the condition and site. (Section 2.2)

Identify Candidate Locations for the Site

• Choose candidate locations based on site requirements.
  • For a regional site, select relatively flat, open terrain removed from local non-weather influences. (Section 3.1)
  • For a local site, select candidate locations close to the road weather condition or road segment of interest or in a position specifically selected to detect and/or predict a local roadway condition (e.g., smoke or dust sources, canyon entrances, sources of road flooding). (Section 3.2)
• Identify power source options and challenges (type, access, cost). (Section 5.2)
• Identify communications options and challenges (type, capacity, frequency of access, cost). (Section 5.3)
• Other considerations (aesthetics, safety, security). (Section 5.4)
• Investigate opportunities to partner with other agencies. (Section 5.3).
  • Identify other sites or sensors to provide weather data that can be used to monitor or predict road weather conditions.
  • Identify infrastructure resources (power, communications, sensor platforms) that can support ESS installation.
• Verify the availability of rights of way to install the site. In some cases, easements or other permits may be required. (Section 4.0)

Identify Sensors Needed

• Choose sensor suite-based requirements.
  • For a local condition or regional site. (Section 2.1)
    • Consider how the observations will be used.
    • What are the required weather parameters at the site of interest and what sensors can measure them directly or provide an indication of their occurrence?
  • For a regional site. (Section 2.1)
    • Select a minimum suite of initial sensors for area coverage based on agency needs.
      • Wind speed and direction.
      • Temperature/dewpoint.
      • Pavement surface conditions.
      • Precipitation presence, type, and intensity.
• Consider additional sensors. (Sections 2.1 and 4.3 and Appendix C)
  • Assess requirements, usefulness, sensor reliability/maintainability, and cost.
    • Atmospheric pressure.
    • Subsurface temperature.
    • Visibility.
    • Precipitation accumulation.
    • Solar/terrestrial radiation.

Select a Specific Site

• Assess surroundings. (Section 4.0)
  • Identify potential obstructions to selected sensors.
  • Identify potential sensor contaminants.
    • Nearby water/dust sources, tree/terrain shadowing.
• Identify tower site (trade-offs required). (Sections 4.0 and 4.1)
  • Assess distance from obstructions/contaminants.
  • Assess specific power/communications access.
  • Assess ease of maintenance and safety considerations for road traffic and maintenance personnel.
• Identify pavement surface sensor locations and lane placement to meet operations and road maintenance requirements. (Section 4.2)
• Identify site(s) for additional sensor(s) separate from tower. (Section 4.0)

Tower and Sensor Siting Recommendations

• Site tower. (Sections 4.1 and 4.2)
  • Flat terrain, not bedrock or swampy, no steep slope within 300 feet (approximately 90 meters).
  • Low vegetation/native soil for 50 feet (15 meters).
  • Upwind of roadway for season of interest.
  • Avoid standing water.
  • Position 30 to 50 feet (9 to 15 meters) from edge of paved surface.
  • Height of tower depends on selected sensor suite; at least 33 feet (10 meters) for wind sensors.
  • Tower base at the same elevation as road surface, if possible.
  • Barrier or guardrail.
  • Security fence.
  • Avoid neighboring structures, signs, and trees or tall vegetation. Towers with wind sensors should be located away from obstacles at a distance of at least 10 times the height of the nearest large obstacle, if possible.
• Site sensors.
  • Atmospheric temperature/dewpoint. (Sections 3.2.2 and 4.2)
    • Shielded, well-ventilated sensor.
    • Height of sensor 5 to 6.5 feet (1.5 to 2 meters).
    • Boom extended from tower at least 3 feet (1 meter).
    • For local low-visibility conditions, consider alternate siting closer to the road or local sources (moisture/dust) to capture local effects.
  • Wind speed and direction. (Sections 3.2.3 and 4.2)
    • Locate the sensor away from obstacles at a distance of at least 10 times the height of nearest obstruction, if possible.
    • Height of sensor 33 feet (10 meters).
    • For high wind conditions, consider:
      • Siting additional sensors at a 10 to 16.5 feet (3 to 5 meters) height to capture local effects.
      • Locating sensors at the entry and/or exit of valleys or canyons to measure high winds due to channeling.
  • Optically-based precipitation (rate, type, and amount). (Section 4.2)
    • Height of sensor 10 feet (3 meters).
    • Avoid sun or stray light sources.
  • Visibility. (Sections 3.2.2 and 4.2)
    • Height of sensor 6.5 to 10 feet (2 to 3 meters).
    • Avoid sun or stray light sources.
    • For local low-visibility conditions, consider alternate siting closer to the road or local sources (moisture/dust) to capture local effects.
  • Snow depth. (Section 4.2)
    • Height of sensor approximately 3.5 feet (1 meter).
    • Ensure proper field of view and orientation.
  • Shortwave solar radiation. (Section 4.2)
    • Height of sensor at least 10 feet (3 meters).
    • Avoid reflective surfaces and shading.
  • Longwave radiation. (Section 4.2)
    • Height of sensor at least 10 feet (3 meters).
    • Ensure clear field of view.
  • Cameras. (Section 4.2)
    • Site as high as possible to obtain clear line-of-sight or at driver’s level, depending on requirement.
    • Ensure non-interference with other sensors.
  • Pavement temperature and pavement condition. (Sections 3.2.1 and 4.2)
    • For local slippery pavement conditions, select location to capture critical condition.
    • In user-specified lane near edge of wheel track, flush with surface.
    • Avoid pavements with ruts or depressions that cause ponding.
    • Avoid shade, unless specific requirement dictates.
    • Utilize junction and pull boxes for ease of installation and replacement.
  • Subsurface temperature/moisture. (Section 4.2)
    • Depth of sensor 12 or 18 inches (30.5 or 45.5 centimeters).
    • Avoid burying under pavement sensors.
  • Precipitation accumulation. (Section 4.2)
    • Place in as open an area as possible.
    • Consider separating from other sensors rather than mounting on the tower.
    • Consider power requirements for winter operation.
  • Barometric pressure. (Section 4.2)
    • Avoid exposure to elements and wide temperature changes.
  • Water level sensors. (Section 4.2)
    • Place in low-turbulent (i.e., steady flowing) portion of the flowing creek or river.
    • If installed on or next to a bridge, locate on the downstream side.
    • For roadway monitoring, place the sensor adjacent to the low point of the road segment subject to flooding.

Metadata (Section 5.6)

• Document site specific installation details.
  
• Update these data whenever changes are made to the ESS installation.