A drive-through scanning system comprises a radiation generating system arranged to generate radiation at two different energy levels and direct the radiation towards a scanning volume, detectors arranged to detect the radiation after it has passed through the scanning volume, and a controller arranged to identify a part of a vehicle within the scanning volume, to allocate the part of the vehicle to one of several categories, and to control the radiation generating system and to select one or more of the energy levels depending on the category to which the part of the vehicle is allocated.