(a) when it is not practical to operate a conventional motor vehicle on the highway due to weather or other conditions and as a result a state of emergency has been declared by the governmental authority having the jurisdiction to make such declaration,

(b) where such person is engaged in the erection, repair, maintenance or inspection of electric power or telecommunication wires or cables which have been or are being erected under, along or upon the highway, to the extent necessary for the purposes of such work, or

(c) where such person is engaged in the inspection, maintenance or repair of any facility or works of a telecommunication or electric power utility requiring access by the highway, to the extent necessary for the purpose of travelling to or from the location of such facility or works at any time when travel upon the highway is physically obstructed by snow or otherwise.