Road Weather Hazard Assessment Challenges in Complex Terrain

Road weather hazards such as snow, ice and heavy rain can make the road surface unsafe for drivers and can cause major traffic problems along a route. Accurate road hazard assessment can inform DOT maintenance managers about where major problems exist along a roadway and also what sections of road need to be treated or closed. Road hazard information can also be relayed to drivers to prevent further weather related accidents and traffic congestion. Until recently the community has relied on conventional methods for determining where road hazards exist, using a combination of surface based observations and short-term weather forecasts from multiple sources, which can result in an inaccurate assessment and poor decision making.  Getting accurate road hazard assessment has been especially challenging over complex terrain where there are often rapidly changing weather conditions, fewer surface observations, and a lack of radar coverage.

In 2012 the Federal Highway Administration (FHWA) initiated a project with the National Center for Atmospheric Research (NCAR) to create a general roadway hazard alert system (Pikalert®) that utilizes mobile observations (when available) along with surface observations, radar data and near-term weather forecasts to indicate where current weather hazards exist along a route and how long the hazard may last based on a near-term forecast. In 2015 the Colorado Department of Transportation (CDOT) initiated a project with NCAR to develop and setup a Pikalert system over Colorado with a focus on road weather hazards along interstate I-70 from Denver to Vail. Recently, in spring of 2016, NCAR started a similar project with the Alaska Department of Transportation to provide road hazard assessment over south-central Alaska. Both Colorado and Alaska are mountainous states with major roadways that go through complex terrain. The complex terrain creates unique challenges for doing hazard assessment and thus new techniques and changes to the hazard alert system in Pikalert® were necessary to provide more accurate road hazard information.

This presentation will discuss the challenges of making road weather hazard assessments over Colorado and to some extent Alaska.  In particular it will focus on changes made to the Road Weather Hazard (RWH) module in Pikalert to deal with complex terrain.  First, an overview of the RWH hazard assessment algorithms (precipitation-type, precipitation-intensity, pavement-conditions, pavement-slickness and visibility) will be presented. Next, there will be a discussion of how these algorithms are impacted by complex terrain especially when there are few if any mobile observations along a route. Lastly, improvements to the RWH algorithms will be discussed including the incorporation of new weather data such as dual-polarization radar data, and RWIS road-state reports.