  Research on adaptive traffic signal control (ATSC) extends back to at least
the 1960s, and many ATSC methods have been proposed over the years. This paper
provides a review of this research and proposes a taxonomy for organizing it,
accompanied by a consistent vocabulary for discussing the control concepts. We
begin from the well-established concept of control generations. Next, we
classify the ATSC methods according to their topographic structure (local-only,
system/hierarchical), time resolution of decision-making (continuous versus
planning-horizon), type of decision (rule-based or optimization), objective
function, cyclic/acyclic nature,and additional subcategories relevant to
certain "families" of methods. These various elements of system control are
organized into a taxonomy of ATSC to help future researchers understand the
wide diversity of algorithmic approaches to the signal control problem that
have been proposed to date, and which can be updated or expanded to incorporate
future research.
