Road Weather Information Systems (RWIS) Expert Article

In this article the highway engineering experts at Robson Forensic provide an introduction to Road Weather Information Systems (RWIS) as they apply to snow and ice management.

Road Weather Information Systems (RWIS)

A Road Weather Information System (RWIS) consists of a network of Environmental Sensor Stations (ESS) connected to a computer. The stations are located adjacent to highways and bridges. Currently, all 48 contiguous states have environmental sensor stations and use RWIS; however, the majority of these stations are located in the Snowbelt states. RWIS provides users, such as state Departments of Transportation, with the ability to make timely and efficient winter maintenance decisions.

RWIS, especially for winter maintenance, can provide decision makers with critical information on the current and future condition of pavement surfaces. This allows those decision makers to be proactive in mobilizing maintenance forces to anti/deice their pavements so as to provide motorists with safer and more efficient travel.

Environmental Sensor Stations (ESS)

ESS atmospheric sensors are mounted on a tower adjacent to a highway and/or bridge. Photo A below shows a typical ESS location. The sensors measure air temperature, dew point temperature, relative humidity, wind speed and direction, precipitation occurrence, precipitation type and intensity, snow depth or stream water level.

Pavement sensors are installed in the pavements of highways and bridges. Photo B below shows a pavement sensor installed on a highway. These sensors measure surface temperature, subsurface temperature (18” below the surface), pavement condition (e.g., wet, dry, icy, etc.), salt concentration (if the road has been salted) and also the freezing point of any moisture present on the pavement. Most environmental sensor stations also include cameras to obtain still and/or video images of the area around the station.

ESS Data

The table below shows data from an ESS. For this specific event, light snow started falling at 01:38 AM. At 02:18 AM, the system sent an ice watch alert to the systems owners/users. Within ½ hour, the users of the system had a truck spread salt on the road. That action turned the surface condition from Ice Watch to Chemically Wet. Chemically Wet means that the pavement is wet, pavement temperatures are below freezing and there is a chemical preventing the wet pavement from turning to ice.

By salting when there was an alert, they were able to prevent ice from forming on the pavement. This was a proactive action. Had they waited for the system to provide an ice warning (which means ice has formed) they would have been spreading salt on top of ice that already formed. Depending on how long it took them to react, there may have already been ice related accidents. This would have been a reactive response.

Highway Engineering Investigations

The municipal and highway engineers at Robson Forensic are frequently retained to determine if the design, construction, or maintenance operations of roadway systems contributed to the cause of motor vehicle collisions, pedestrian strikes, or other injuries.

For more information submit an inquiry or visit our Highway Engineering practice page.