Road weather information systems

Road weather information systems (RWIS) monitor local roadway and weather condition information and alert an agency and the traveling public about inclement weather conditions. It can be highly customized to the specific weather conditions and detection needs of a given location.

Key characteristics




WSDOT regions

Other names

  • Environmental sensor stations

Strategy description

Weather conditions such as rain, snow, and cold temperatures can create unsafe roadway conditions for travelers. Road weather information systems (RWIS) collect, aggregate, and communicate road weather information to inform travelers to prepare for adverse driving conditions or avoid them altogether. RWIS is especially valuable at locations such as mountain passes that experience severe weather conditions. RWIS helps assess road weather conditions to determine whether chains are required, roads or passes to close, and alternate routes to recommend.

An agency’s RWIS will typically include multiple environmental sensor stations (ESS) installed at key locations throughout the roadway network to measure atmospheric, pavement, and/or water level conditions. Specialized sensors on the ESS collect real-time temperature, humidity, wind speed, pavement temperature, and pavement conditions data, and report it to a central RWIS software application.

More recently, mobile sensor technology mounted on fleet vehicles has been used to provide RWIS systems additional pavement and atmospheric conditions data to complement the information that is collected by fixed sensor stations.

Once the weather data from the various sensors is aggregated, the key function of the RWIS is to turn it into useful and actionable information. Information about hazardous road conditions can be disseminated to travelers through an agency’s traveler information data delivery channels, including variable message signs, highway advisory radio, and other traveler information applications supported by the agency. More advanced RWIS functions include the automatic activation of warning systems (e.g.,curve warning, variable speed limits) when certain thresholds are met.

Advanced RWIS integrate other external weather data information, including weather forecasting services and crowd-sourced data (e.g., citizen reporting programs, Waze). As connected vehicle technology advances, standard vehicle status information (e.g., windshield wiper activation, anti-lock brake status, air temperature readings) may be another mobile data source for RWIS.

When to use this strategy

RWIS makes sense for highways and other major corridors that experience hazardous weather conditions. ESS should be installed at specific roadway locations with known adverse weather issues, especially at bridges, mountain passes, or flood-prone areas. RWIS is applicable for jurisdictions that want to integrate weather data into operational plans, including winter maintenance (i.e., snow plows, de-icers) activities and active traffic management (ATM) strategies

Strategy benefits:

  • Improved safety through traveler awareness and preparation for adverse conditions
  • Heightened organizational preparedness for weather-related traffic incidents
  • Improved understanding of the impact that weather has on roadway performance through continuous data collection and analysis
  • Improved usefulness of an agency’s existing traveler information systems by expanding the scope of information that can be provided to travelers

What you need in order to implement

Policy needs:

  • Agency standards for road weather traveler information dissemination, including desired messaging on the signs, integration with other traveler information systems, and data sharing policies and standards

Planning needs:

  • Conditions analysis to identify key locations for sensor stations and the type of road weather information that should be collected at these locations
  • Operational plans detailing what the agencies will do in response to certain weather conditions; e.g., what conditions warrant requiring chains or closing a mountain pass or roadway

Coordination needs:

  • Coordination with the applicable road owners, centralized traffic management center, winter maintenance groups, and external data providers such as weather forecasting services and crowd-sourced data providers

Equipment needs:

  • Environmental sensor station (ESS) at key roadway locations to measure atmospheric, pavement, and weather conditions
  • Communications device that transmits weather data to a central location
  • Central system for collecting, processing, and reporting on field data
  • Roadside variable message signs to provide warnings and alerts
  • Cameras to verify road weather conditions

Maintenance needs:

  • Regular maintenance of environmental sensors and communications systems
  • Regular testing and validation of the environmental sensors to confirm that conditions are detected reliably and accurately

Agency resources needs:

  • Engineers to design placement ESS, establish proper weather warning messaging, and make modifications to the system
  • Traffic management center operators to operate and monitor the RWIS system

Learn more about this strategy

Federal Highway Administration (FHWA), Best Practices for Road Weather Management version 3.0.

Michigan Department of Transportation Road Weather Information System (RWIS) Evaluation Technology Evaluation Memorandum (PDF).

About key characteristics

Location notes:

RWIS sensors are installed at locations along freeways or other roadways that experience hazardous weather conditions, especially at bridges, mountain passes, or flood-prone areas.

Cost notes:

Given that RWIS environmental sensor stations are often in remote locations, the most expensive portion of an RWIS is installing the communications and power to these stations.  Agencies should consider the accessibility of potential station locations when evaluating station siting options.

Technology notes:

Technology needs vary depending on the sophistication of RWIS system, including the types of weather sensors used, the degree of integration with traveler information systems, and whether RWIS data is being used in automated active traffic management strategies (e.g., variable speed limits) or winter maintenance operations.

Collaboration notes:

Collaboration needs are relatively low as the RWIS system is typically operated by a single agency (usually a state DOT) on that agency’s roads. However, for RWIS systems that integrate external data sources or work with third-party data providers to disseminate traveler information, collaboration with these external partners is necessary.