Prior to this work, MASSVAC (MASS eVACuation) had evolved as a micro-computer simulation model for analysis and evaluation of areas facing natural disasters (hurricanes and floods). Conceptual and technical enhancements have been made to procedures within MASSVAC to deal with the special problems of evacuating around nuclear power stations. Its incorporation into TEDSS-3 (Transportation-Evacuation Decision Support System) has resulted in a powerful tool to assist development of evacuation plans for nuclear power plants. The computer package comprehensively provides for all functions related to evacuation planning such as development of a socioeconomic and highway network database, estimation of evacuation time and development/evaluation of traffic management strategies to reduce network clearance times and to improve highway network performance during evacuation. Primary focus is on the new features incorporated into MASSVAC, especially in the trip distribution and traffic assignment procedures. Significant improvements have been made to the software implementations of the Dial traffic assignment and other key algorithms used in MASSVAC. The information content of the model's output has been enhanced for better understanding of the evacuation process and presentation of results. / Master of Science