The effect of active flow control (AFC), using oscillatory blowing (synthetic jets) and steady suction/blowing, on drag reduction of cars/trucks is numerically studied using the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations. Three generic models of trucks for which the experimental data are available are considered in the simulations. CFD simulations are in good agreement with the data. Both the experiments and simulations show that 10 to 15% reduction in drag can be achieved by active flow control using oscillatory blowing. A combination of oscillatory blowing and steady blowing or suction at appropriate locations on the rear face of the truck can further reduce the drag. These studies indicate that the AFC techniques can be intelligently employed to achieve significant reduction in aerodynamic drag of the vehicle.