An interrogating system can include an interrogating apparatus configured to transmit toward and receive from a subject in a subject position, millimeter-wave electromagnetic radiation. Such a system can also include a controller configured to operate the interrogating apparatus, and produce data representative of a characteristic of the subject from received radiation. Some embodiments of such an interrogating system may include interrogating apparatus adapted to be mounted to a passenger vehicle or at a vehicle passenger loading zone, to interrogate passengers prior to boarding the vehicle. Such embodiments may include one or more controllers positioned within the vehicle or at the loading zone.