A Downhill Grade Severity Rating System

Johnson, Walter A.; Myers, Thomas T.; DiMarco, Richard J.; Allen, Robert B.

doi:10.4271/811263

Cited by 9 publications

(3 citation statements)

References 2 publications

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“…The purpose of the algorithm based on the updated GSRS model with horizontal curvature inclusion is to determine the maximum speed at which a truck can descend the combined downgrade and initiate curves without exceeding the maximum temperature limit of the braking system or the speed limit of the road, and without overturning or skidding. Based on a study conducted by Johnson et al ( 23 ), 500°F or 530°F was determined as an appropriate value for the maximum allowable temperature depending on the lining material.…”

Section: Methodsmentioning

confidence: 99%

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

Ampadu

Alrejjal

Ksaibati

2022

Transportation Research Record: Journal of the Transportation R

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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.

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Section: Methodsmentioning

confidence: 99%

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

Ampadu

Alrejjal

Ksaibati

2022

Transportation Research Record: Journal of the Transportation R

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“…Highway safety and operating guidelines indicate that the safe speed recommendation feature of the WSS can effectively reduce the downhill speed of trucks (21). At the same time, other studies were carried out to verify and improve the FHWA GSRS model through simulations, test data, and other methods (17,(22)(23). Another study was also carried out on an MS-DOS computer program that used the FHWA model to calculate the maximum safe vehicle speed on downhill sections.…”

mentioning

confidence: 99%

Safe Speed Prediction Model for Heavy Trucks on Consecutive Mountain Downgrade Routes Based on Energy Conservation Law

Yan

Han

et al. 2021

Transportation Research Record

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Safe vehicle speed estimation is essential for road traffic management and traffic safety. Improper truck speed on downgrades may lead to brake fade and/or failure, resulting in severe truck accidents such as runaway or out-of-control. This paper presents a model for predicting the safe speed of trucks from the perspective of preventing brake failure. The proposed model can be used to control the speed limit or as a reference for the revision of highway geometric design standards. In addition, by considering the downgrade design speeds recommended by AASHTO, the study offers an approach to deciding the downgrades that need escape ramps, those that need different speed limits, and those that may need exclusions for trucks over a certain weight. First, we simplify the downgrade driving status of a heavy truck into three types: speed control, emergency braking, and speed recovery according to the speed change status. The prediction model of the brake drum temperature with speed variables has been established in our previous study based on Newton’s energy conservation law. Finally, the boundary conditions for brake fade and failure temperature are determined. Results of parameter analysis show that the gross truck weight is the most significant variable. Other significant variables are grade, grade length, and emergency braking time. Compared with previous research results, the advantage of this method is that the permitted speed can be derived using the brake temperature prediction model supported by theory, without the need for extensive field tests.

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“…The probability of truck crashes occurring on downgrades is higher than on level terrain because of the increased likelihood of a runaway. A runaway vehicle, as defined by Johnson et al, is “a vehicle whose speed, headway, or directional controls are aggravated by a downgrade such that the chances of a crash are substantially increased for a given set of road, traffic, and environmental conditions” ( 1 ). Truck brakes generate large amounts of heat energy on downgrades which has to be absorbed by the brakes.…”

mentioning

confidence: 99%

Evaluating the Safety Effectiveness of Advance Downgrade Warning Signs in Preventing Downgrade Truck Crashes using a Propensity Scores Framework

Moomen

Rezapour

Raja

et al. 2019

Transportation Research Record

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Truck crashes on steep downgrades exact devastating tolls on lives and property. An important intervention to reduce the frequency of truck crashes on downgrades has been to present quality information to drivers about upcoming downgrades through warning signs. The use of advance warning signs on downgrades to prevent truck crashes is the current state of practice for most highway agencies; thus, it is critical to assess the safety effectiveness of such warning signs. Though several studies have evaluated the efficacies of warning signs, the safety effectiveness of advance downgrade signs is less clear. This study uses a propensity scores framework to assess the effectiveness of current downgrade warning signs by matching treated and untreated downgrade segments in Wyoming. The advantage of propensity score matching over other traditional analysis techniques is that it reduces bias in safety evaluation by mimicking randomization and accounts for confounding factors. Using the risk ratio computed from the matched data, the study found that advance downgrade warning signs are effective in reducing downgrade truck crashes. The results indicate that truck crash risks on downgrades without advance warning signs are an estimated 15% higher than downgrades with advance downgrade signs. The 90% bootstrap confidence interval for the risk ratio was found to be from 1.04 to 1.53.

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A Downhill Grade Severity Rating System

Cited by 9 publications

References 2 publications

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

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

Safe Speed Prediction Model for Heavy Trucks on Consecutive Mountain Downgrade Routes Based on Energy Conservation Law

Evaluating the Safety Effectiveness of Advance Downgrade Warning Signs in Preventing Downgrade Truck Crashes using a Propensity Scores Framework

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