Given an interval order on a topological space, we
characterize its representability by means of a pair of upper semicontinuous real-valued functions. This characterization is only based on separability and continuity conditions related to both the interval order and one of its two traces. As a corollary, we obtain the classical Rader's theorem concerning the existence of an upper semicontinuous representation for an upper semicontinuous total preorder on a second countable topological space.
