عنوان مقاله [English]
Ride comfort and sight distance are two main parameters of designing roads vertical curves. Vertical acceleration is one of the most important criteria for measuring ride comfort in vertical curves. Vertical acceleration equations in geometric design of roads literatures, such as Green Book of AASHTO, are based on point mass model where vehicle is assumed to be a point object with a specific mass. Considering vehicle is a multi-body system, dynamic responses of each part of this system can be different from a point object. In this study, dynamic simulation’s CarSim and TruckSim software utilizing Multi-Body (M-B) model are used to investigate the vertical acceleration more accurately, and to compare it with the vertical acceleration of the point mass model. The dynamic responses of three types of vehicles have been investigated under different speeds and grades. The results show a significant difference between the results of the two models depending on the vehicle speed and the road grade, and the point mass model suggest less acceleration. As, difference of the vertical acceleration between the point mass model and the M-B model depending on the vehicle speed and the road grade are ranged for Sedan between 12.6% to 25.9%, for SUV between 23.8% to 29.1% and for the truck between 29% to 47.6%. According to the results of this study, to design vertical curves, the use of M-B dynamic model, according to more accurately simulate the vehicle, deliver a more accurate and realistic design.