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Truck crashes on steep downgrades caused by excessive brake heating is an ongoing concern for the Wyoming Department of Transportation (WYDOT). Crashes resulting from brake failure on downgrades cause a devastating toll on lives and property. To counter such crashes, WYDOT initiated a research project in 2016 to update a previous Grade Severity Rating System (GSRS) model originally developed in 1981.
Current truck characteristics have undergone significant changes over the decades. As a result, updating the GSRS was necessary since the previous GSRS model is now considered insufficiently representative of current truck characteristics.
This study sought to fulfill Phase II of the GSRS study which specifically aims to enhance the Grade Severity Rating System by achieving three main objectives. The first objective is to validate the GSRS model for trucks that have only drum brakes installed. The second objective is to make the updated GSRS fully implementable by incorporating horizontal curves into the formulation of the weight specific speed (WSS) signs. The final objective is to develop a software that simplifies the implementation of the GSRS and the formulation of WSS signs. The software has been developed using a graphical user interface (GUI) that takes inputs of the physical characteristics of a downgrade, truck weight, and initial brake temperature, and gives maximum speeds for different weight categories as output. The software is able to estimate and display maximum descent speeds for two scenarios: single and multi-grade hills using the Continuous Slope and Separate Downgrade technique respectively.