Investigation of Vertical Acceleration of Vehicles in Vertical Curves Using Multi-Body Dynamic Model

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 in the literature, 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 that vehicle is a multi-body system, dynamic responses of each part of this system can be different from a point object. In this study, CarSim and TruckSim dynamic simulation softwares utilizing Multi-Body (M-B) model are used to investigate more accurately the vertical acceleration, and to compare it with the vertical acceleration of the point mass model. Dynamic responses of three types of vehicles have been investigated under different speeds and grades. Results indicated a significant difference between the results of the two models, depending on the vehicle speed and the road grade, and the point mass model suggested less acceleration such that difference of the vertical acceleration between the point mass model and the M-B model, depending on the vehicle speed and the road grade, ranged 12.6-25.9% for Sedan, 23.8-29.1% for SUV and 29-47.6% for the truck. According to the results of this study, to design vertical curves, the use of M-B dynamic model, according to more accurate simulation of the vehicle, delivers more realistic design.