  Zero forcing is a process on graphs in which a color change rule is used to
force vertices to become blue. The amount of time taken for all vertices in the
graph to become blue is the propagation time. Throttling minimizes the sum of
the number of initial blue vertices and the propagation time. In this paper, we
study throttling in the context of directed graphs (digraphs). We characterize
all simple digraphs with throttling number at most $t$ and examine the change
in the throttling number after flipping arcs and deleting vertices. We also
introduce the orientation throttling interval (OTI) of an undirected graph,
which is the range of throttling numbers achieved by the orientations of the
graph. While the OTI is shown to vary among different graph families, some
general bounds are obtained. Additionally, the maximum value of the OTI of a
path is conjectured to be achieved by the orientation of a path whose arcs
alternate in direction. The throttling number of this orientation is exactly
determined in terms of the number of vertices.
