Abstract
Reverse Horizontal Curves (RHCs) are among the most accident-prone road points, with many annual fatalities and injuries. These fatalities can increase dramatically if the RHCs and longitudinal slopes are combined. The importance of increasing the safety of RHCs, especially in mountainous routes, is doubled due to the possibility of combining RHCs with vertical extensions or combining them with so-called steep slopes. This study used vehicle dynamic modeling to evaluate the lateral friction of various vehicles. Including the E-Class Sedan, E-Class SUV, Truck, and Bus, moving on RHCs combined with a longitudinal slope (downgrade, upgrade, and direct distance). Then, the RHC lateral friction model was presented using the multiple regression model based on the effective parameters, including design speeds, direct distance, and different longitudinal slopes. The results showed that speed, longitudinal slope, and vehicle type had the most impact, and direct distance had the most negligible impact in friction coefficient models. Based on the modeling results, the higher the design’s speed and the shorter the direct distance, the lower the lateral friction coefficient for the Sedan and SUV. Hence, the safety of the vehicles is greater. For trucks, reduced speed, increased direct distance, and reduced slope led to increased safety. In the results, the most critical state was the lateral friction coefficient at a speed of 80 km/h and a direct distance of 116 m for the SUV.
Highlights
Reverse Horizontal Curves (RHCs) are among the most accident-prone road points, with many annual fatalities and injuries. ese fatalities can increase dramatically if the RHCs and longitudinal slopes are combined. e importance of increasing the safety of RHCs, especially in mountainous routes, is doubled due to the possibility of combining RHCs with vertical extensions or combining them with so-called steep slopes. is study used vehicle dynamic modeling to evaluate the lateral friction of various vehicles
Including the E-Class Sedan, E-Class SUV, Truck, and Bus, moving on RHCs combined with a longitudinal slope. en, the RHC lateral friction model was presented using the multiple regression model based on the effective parameters, including design speeds, direct distance, and different longitudinal slopes. e results showed that speed, longitudinal slope, and vehicle type had the most impact, and direct distance had the most negligible impact in friction coefficient models
Due to the possibility of combining RHCs with steep slopes, the importance of increasing the safety of Reverse Horizontal Curves (RHCs) on mountain trails is of greater importance. e American Association of State Highway and Transportation Officials (AASHTO) considers a maximum value of 1.5 for the ratio between the larger radius and the smallest reverse radius [7] and does not provide any other instructions for correcting the geometry of RHCs combined with the extension of the route
Summary
Various researches have studied the safety effects of road geometry related to pavement conditions along with some changes in pavement surface conditions. Kordani et al presented the following model to calculate the lateral friction coefficient in a horizontal curve combined with longitudinal slopes and in different conditions by simulating the movements of light and heavy vehicles such as E-class Sedan, SUV, and truck. The effect of a horizontal curve combined with longitudinal slopes was investigated by simulating the light and the heavy vehicles at different speed. The lack of a safety-base study that can simultaneously incorporate vehicle parameters into the proposed model encouraged the authors to use the dynamic vehicle modeling method and examine the safety of different vehicles passing through the RHC by considering the lateral friction coefficient as the main variable, given the use of RHC and RHC combined with the upgrade and downgrade slopes (especially on mountain roads)
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