Electronic Equipment Variable-message signs, or VMS, are electronic equipment which may display different traffic messages consistent with the requirements of a selected road. Permanent VMS displays are mounted on large sign structures overhead or alongside the road. These devices are often placed on urban freeways which have traffic problems. Portable CMS (PVMS) panels are usually mounted on trailers, although some could also be carried by trucks. they're often utilized in work zones or other events that disrupt .