(a) Vehicles directly crossing a highway at, or approximately at, right angles;

(b) Vehicles used in the construction, reconstruction or repair of a highway when at the site, or within the contract limits (as defined in the designation of a restricted highway) of, such construction, reconstruction or repair activity;

(c) Vehicles used for applying abrasives or chemicals for snow and ice control on a public highway while such vehicles are actually engaged in such operation or traveling to a particular location for such purpose.