In this paper, we discuss work aimed at the development of interactive decision-support tools for complex, large-scale scheduling applications. Our approach is grounded on three basic premises: (1) that system organization and decision-support "services" should directly reflect the inherently reactive nature of decision-making in complex scheduling environments, (2) that diversity in the character and requirements of various user tasks will invariably require different specialized scheduling services in different decision-making contexts, and (3) that problem scale and complexity will necessitate user interaction at aggregate, task-oriented levels. We describe DITOPS, a transportation scheduling tool which integrates a hierarchical modeling infra-structure and reactive scheduling methodology with graphical schedule visualization and manipulation capabilities to provide a flexible interactive environment for construction and management of transportation schedules.