Incorporating Horizontal Curves and Roadway Geometry into the Automated Updated Grade Severity Rating System

Highway agencies all around the country, including the Wyoming Department of Transportation (WYDOT), have deep concerns about truck crashes resulting from brake temperatures exceeding the critical brake temperature as they descend steep downgrades. Through a series of research initiatives starting in the 1980s, WYDOT has developed a Grade Severity Rating System (GSRS) to estimate the maximum safe speed for trucks during downgrade descent. In 2020, the updated mathematical model was automated through an interactive, intuitive, aesthetically appealing, and user-friendly objected-oriented Visual Basic.net software. Additional research on the GSRS model was commissioned by WYDOT to account for large truck vehicle stability—specifically, rollovers and skidding/side slip during grade descent. These scenarios become relevant in the presence of horizontal curves. Consequently, this latest mathematical model has been automated to simplify the computation of maximum safe descent speed on the downgrades combined with curves, all based on the truck weight. As in the previous version of the software, it provides functionality for both the continuous slope and the separate downgrade method. The primary beneficiaries of the software will be highway agencies who will be able to estimate the maximum safe speed of descent for trucks descending downgrades with horizontal curves at various weight categories and therefore produce Weight Specific Speed (WSS) signs for each downgrade or multi-grade section.