Road Weather Information Systems & Winter Maintenance Operations Expert Article

In this article, Civil Engineer, Thomas Lyden provides an overview of Road Weather Information System in winter maintenance operations. His discussion includes identifying the sensors that are often installed in a RWIS station, the ways in which highway agencies and motorists benefit from RWIS, duties that may result from implementing a RWIS system, and resource decisions that can be made based on current and forecasted weather conditions.

RWIS expert article

The unpredictable nature of winter weather and the variability of local roadway conditions have traditionally been the greatest challenges for effective winter maintenance operations. However, Road Weather Information Systems (RWIS) have the potential to provide maintenance managers with the necessary information to strategically deploy resources based on real time local conditions.

Road Weather Information System stations contain a suite of sensors which measure meteorological and pavement conditions. Air, pavement, sub-surface temperature, wind speed and direction, and precipitation type and intensity are a few of the measured conditions. Installing sensors in the highway or bridge pavement surface allows the pavement status (dry, wet, chemically wet, ice) to be known and treated. In some applications, cameras are integrated into the stations to capture still or video images. These images provide a visual confirmation of the sensor data and provide maintenance managers with eyes in the field to assess and address highway conditions.

Highway Agencies and Motorists Benefit

RWIS provides highway agencies with critical weather information, allowing maintenance managers to make more informed decisions. In winter maintenance operations, RWIS assists in determining when and where resources should be deployed to address dangerous snow and ice conditions.

Sensors combined with variable message signs installed near known problem areas warn motorists of impending hazards. For example:

  • Pavement surface condition status sensors may activate a notice to highway message boards warning motorists to slow down and be alert to icy conditions.
  • Water level instruments combined with a warning system for flood detection may require road closure warnings.

These site specific warnings may command motorist respect as opposed to wide-reaching general advisories issued through media outlets. Motorists can be warned to take responsible action at hazardous locations.

Highway agencies often provide public access to all or a portion of RWIS information to traveler information web sites, in an effort to enhance driver safety by preparing drivers for adverse weather conditions before they begin their journey.

RWIS Raises Expectations

The use of RWIS systems and monitoring stations has become more widespread, as has the use of variable message signs on the highway, and message dissemination channels. With this increase in utilization and message visibility, motorists have begun to trust in the accuracy and reliability of this information in both pre-trip planning and in-trip advisories.

Agencies are advised to implement a routine maintenance and calibration procedure program to ensure the accuracy of the data and reports coming from their RWIS. Due to the harsh highway environment, sensitive instrumentation and mission critical sensors placed there can drift from a true reading or fail. Maintenance managers accustomed to relying on RWIS data to deploy resources for safety critical functions may deploy too early, too late, or lose confidence in the system altogether. States that have established RWIS but failed to properly maintain their system have suffered the consequences when systems fail during weather emergencies and force service to be suspended.

RWIS systems may exceed the budget of smaller agencies. However, having sensor stations located near the agency’s jurisdiction that provide adverse weather data to the general public is a valuable resource to those smaller highway departments. Traditional weather reports and forecasts provided by the National Weather Service or media sources are for large areas, and define average conditions or a range of conditions. Sensors located nearby that are operated by a larger sister agency are more likely to represent local conditions, leading to timely response plans. Often, agencies will execute a data-sharing agreement to gain access to the full range of data, beyond what is shared with the general public.

Changing Weather Conditions

Forecasting is a key element to RWIS. Contract meteorologists or trained individuals within the agency are needed to interpret and analyze current meteorological data and then assess how that information will affect the roadway environment in the near future. For example, a forecast of air, dew, and pavement temperatures allows an assessment of whether black ice or frost may form on bridges or pavement surfaces. While maintenance managers can be trained in forecasting, their primary role is to focus on preparing and deploying resources, so it is important that the data that has been collected is presented in a manner that makes for timely analysis and decision making.

Having multiple RWIS stations allows the maintenance manager to more accurately foresee changing weather conditions and patterns, and make tactical decisions during a storm. Changing wind speed and direction combined with lowering pavement temperature and increased snowfall as a storm progresses through a region may require a response from an anti-icing strategy to a deicing strategy. It is often required for resources to be reallocated from one area to another within an agency’s jurisdiction, or from tertiary to primary routes, based on the condition of the pavement or intensity of the storm. Posting changing highway conditions to traveler information sites gives notice to drivers to make responsible changes to their travel plans.

RWIS in Forensic Investigations

The appropriate and timely response to RWIS information is the most frequently contested issue involving this technology. As experienced maintenance managers, the forensic experts at Robson Forensic provide credible opinions regarding an agency’s ability to predict and respond to adverse weather conditions. In addition to these analyses, our experts also investigate matters where the maintenance of RWIS infrastructure is challenged.

For more information contact the author of this article or submit an inquiry.

Featured Expert

Thomas Lyden, Civil Engineer & Highway Engineering Expert

Thomas Lyden, P.E., PMP

Civil Engineer & Highway Engineering Expert
Thomas Lyden is a civil engineer with an impressive background covering the entire lifecycle of highway infrastructure. Through his nearly 40 years of professional experience, Thomas has conducted… read more.


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