Unlike traditional Type I dilemma zones, where inappropriate signal timings or detector placements restrict the ability of motorists to safely proceed through the intersection or safely stop in advance, Type II dilemma zones are attributed to driver difficulties in decision making. Type II issues become more prevalent at high-speed intersections, which have greater variability in operating speeds and greater potential for serious crashes. Although several features related to Type II dilemma zones are known, inconsistency remains in the application of the boundary definitions. This research characterizes driver behavior and comprehension related to Type II dilemma zones for the purpose of defining these boundary conditions. Empirical observations of 10 high-speed signalized intersection approaches were conducted, and the analyses of the observed driver behavior resulted in an expanded understanding of how and where drivers make their decision to stop or proceed when approaching a signal. Specifically, distributions of vehicle location and driver behavior were examined using multiple boundary definitions, and in several instances the distributions of driver behaviors varied depending on the dilemma-zone definition employed.