Developing a Vehicle Dynamic Model to Study Roadway and Vehicle Factors in Speed Profile Formation

Accurate speed profiles for various vehicle types play a crucial role in the highway design assessment, highway evaluation packages, and simulation programs. Especially for the design of highways in mountainous areas, the speed profile of trucks on upgrade sections of the highway is essential for determining the length of the grade, assessing the necessity of providing climbing lanes, as well as determining the length of these lanes. Providing the climbing lanes is an effective measure to increase the capacity of the highway, improve traffic operations, and enhance the safety of road users.

Several methods have been used by researchers to develop speed profiles and the role of different factors on the vehicle’s performance. Traditionally, speed profiles are derived from graphs found in highway design manuals such as AASHTO. However, these graphs are limited as they are based on specific weight-to-power ratios, which can vary significantly among vehicle types and cargo loads. To address this limitation, complex computational methods have been deployed to develop microscopic simulation programs like TruckSIM.

In this study, a simple computerized method based on the vehicle dynamics, has been developed to calculate the speed profiles considering various influencing factors. The developed model’s validity was confirmed by comparing results with graphs generated by the TruckSIM simulation software. The model results were also compared to similar studies to ensure the validity of the model. The model results highlight that the most important factor affecting a vehicle’s performance on grades is the weigh-to-power ratio. It was found that the vehicle’s motor power significantly impacts its performance. However, with equal weight-to-power ratios, performance variations are minimal. The type of pavement and the pavement conditions were also found to have a relatively considerable effect on the speed profile. However, the type of tire and the characteristics of that was not found to have a significant effect. The truck configuration was also found to not have a considerable effect on the speed profile.