With the current high level of security awareness in the transit environment and the considerable proportion of bomb threats that are hoaxes, law-enforcement and transit-security officials need decision-making tools to investigate threats before taking action. The use of technology is one option for safely investigating bomb threats. Some transit agencies deploy bomb-sniffing canine unites, but the dogs can only work a short period of time before they are fatigue. This report addresses the need to determine the usefulness of existing portable explosive detection devices (EDDs) in a transit environment . The technology is predicated on trace-vapor detection of explosive residues using mobility spectrometry.