(a) at the junction of numbered State highways when one such highway terminates in a dead end within the boundaries of the Adirondack or Catskill Park;

(b) at the junction of a numbered State highway and a secondary road, when the business to be advertised is located on such secondary road;

(c) at the junction of secondary roads, where the business to be advertised is located on one of such roads;

(d) at the junction of a private road and a public highway when the sign directs, via the private road, to a place of business not abutting such public highway.