Driving stability can be an issue for heavy vehicles. In a side wind, a side force and rolling moment will develop, and they both affect driving stability, from which the vehicle may overturn. It is important to understand the flow structure in order to prevent a truck from rolling over. The main purpose of this study is to investigate the flow around a heavy vehicle that causes it to overturn. A 1/8 scaled, simplified tractor/trailer configuration called the Ground Transportation System (GTS) with Reynolds number (based on the GTS width) equal to 1.6 × 106 was used for this study. A side wind was modeled by turning the GTS model with respect to its moment reference point. A triangular mesh was used for the truck and the computational domain surfaces, while hybrid meshes filled the computational domain volume. The Ansys® CFX code based on the k-ω shear stress transport (SST) turbulence model was used to solve the governing equations numerically for an incompressible fluid. All results were averaged for 50 shedding periods. The simulation was done for yaw angles of 0-14°, and the results were compared with experimental data from the literature. To model an open road, a moving-ground boundary condition was implemented in the simulation. The computational fluid dynamics calculations for the drag, side force, and rolling moment coefficient had more than 90% accuracy. The other aerodynamic coefficients had larger discrepancies due to the moving-ground boundary condition and an under-prediction of the pressure distribution on the front corner radius of the GTS. In general, it was found that the present simulation can capture the trends for most aerodynamic coefficients. This study showed that the rolling moment, which determines the tendency to overturn, is sensitive to the spanwise pressure at the rear of the vehicle.