The effects of vortices trapped between a flat plate and a ground plane were studied in a wind tunnel experiment. The flat plate was mounted parallel to the ground to represent the lower surface of a generic road vehicle. Rectangular vortex generators mounted onto the plate were used to generate streamwise vortices between the plate and the ground plane. The main variables investigated were the ground clearance and vortex generator orientation, both influencing the trapped vortex strength. The experimental data indicates that considerable aerodynamic loads can be created with such vortex generators, particularly for small ground clearance values (even at zero plate incidence).