Comparison of traffic assignments in evacuation modeling

The Nuclear Regulatory Commission (NRC) requires that all electric utilities develop and update evacuation plans for the areas surrounding their nuclear power plants. The evacuation of people around these plants has certain peculiar transportation-related characteristics, such as the location of the incident is fixed, the evacuation area is predetermined by NRC, and all the inhabitants must be evacuated from the affected area. These characteristics pose a challenge to evacuation planners and modelers. The developed evacuation models should incorporate these characteristics and address the peculiarities of the evacuation process. Hobeika et al. have developed a mass evacuation computer program (MASSVAC 3.0) that models the evacuation process and utilizes the traffic assignment of all-or-nothing and Dial's algorithm to simulate the traffic movements during evacuation. The objective of this paper is to describe the upgrade of MASS-VAC 3.0 to MASSVAC 4.0, which incorporates new modeling features such as the user equilibrium (UE) assignment algorithm, which was not available in MASSVAC 3.0. The focus of this paper, however, is on comparing the assignment results of Dial's algorithm with the UE algorithm using performance measures such as the evacuation time, the number of congested links, and the computer execution time. The results show that the evacuation performance measures are largely dependent on the highway network structure and the number of vehicles produced in an emergency planning zone, Generally, it was found that the UE algorithm was more efficient than the Dial's algorithm in the three performance measures mentioned above.