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Project Details

Title:Proposing New Speed Limit in Mountainous Areas Considering the Effect of Longitudinal Grades, Vehicle Characteristics, and the Weather Condition
Principal Investigators:Amirarsalan Mehrara Molan and Khaled Ksaibati
University:University of Wyoming
Project #:MPC-574
RiP #:01674912
Keywords:geometric design, highway grades, highway safety, mountain roads, simulation, speed limits, weather conditions


The current method of Green book (AASHTO 2011) for assigning design speed (and consequently for speed limit) of roads is based on a point-mass model. Therefore, many effective variables such as longitudinal grades, vehicle characteristics, and weather condition are ignored. This fact creates serious safety problems in mountainous areas since, where these missing parameters are dominant. The condition becomes even worse because many of the mountainous roads were built many years ago based on the old design methods (for example, with the downgrades sharper than 10%). This project seeks to study the effect of different parameters related to geometric features (including the radius of the horizontal curve, superelevation rate, and longitudinal grade), vehicles characteristics (including type, weight, and the braking forces), and the weather condition (including side friction factor, wind speed, and wind direction). This analysis will be conducted using a comprehensive series of TruckSim and CarSim simulation tests on the most hazardous mountainous roads in Wyoming. Afterward, appropriate values of speed limit will be proposed for roads tested in the study. Also, new analytical models will be presented to be practical for the rest of the roads (not considered in the study) based on their geometric features, design vehicle, and weather condition.

NDSU Dept 2880P.O. Box 6050Fargo, ND 58108-6050