Determination of an optimal departure schedule is the key issue for a successful staged emergency evacuation for reducing unnecessary network congestion and decreasing the evacuation clearance time. However, flow-related stochastic events, such accidents and short-term traffic breakdowns, bring numerous challenges for developing a reliable evacuation plan with an optimal departure schedule. In order to assist the decision makers for evaluating potential planning risks, this study proposes a modeling framework and a corresponding solution approach that incorporates flow-related accidents and breakdowns into a staged emergency evacuation model. A bi-level stochastic programming problem is formulated. In the upper level, we introduce planning risk by using Mean-Mean Absolute Deviation (Mean-MAD), which is a common measure employed for risk-averse planning. In the lower level, System Optimum Dynamic Traffic Assignment (SO-DTA) formulation, proposed in , is modified as a tool for quantifying the performance of the proposed multistage stochastic traffic assignment approach. The applicability of the proposed framework and solution approach is illustrated by a numerical example designed to depict salient features of the proposed risk-based planning methodology.