Route assignment

Abstract: Shelters are safe facilities that protect a population from possible damaging effects of a disaster. For that reason, shelter location and traffic assignment decisions should be considered simultaneously for an efficient evacuation plan. In addition, as it is very difficult to anticipate the exact place, time, and scale of a disaster, one needs to take into account the uncertainty in evacuation demand, the disruption/degradation of evacuation road network structure, and the disruption in shelters. In this study, we propose an exact algorithm based on Benders decomposition to solve a scenario-based two-stage stochastic evacuation planning model that optimally locates shelters and that assigns evacuees to shelters and routes in an efficient and fair way to minimize the expected total evacuation time. The second stage of the model is a second-order cone programming problem, and we use duality results for second-order cone programming in a Benders decomposition setting. We solve practical-size problems with u...

Abstract: Conventional emergency evacuation plans often assign evacuees to fixed routes or destinations based mainly on geographic proximity. Such approaches can be inefficient if the roads are congested, blocked, or otherwise dangerous because of the emergency. By not constraining evacuees to prespecified destinations, a one-destination evacuation approach provides flexibility in the optimization process. We present a framework for the simultaneous optimization of evacuation-traffic distribution and assignment. Based on the one-destination evacuation concept, we can obtain the optimal destination and route assignment by solving a one-destination traffic-assignment problem on a modified network representation. In a county-wide, large-scale evacuation case study, the one-destination model yields substantial improvement over the conventional approach, with the overall evacuation time reduced by more than 60 percent. More importantly, emergency planners can easily implement this framework by instructing evacuees to go to destinations that the one-destination optimization process selects.

Abstract: The objectives of this study were to improve the understanding of travel behavior and to enhance practical transportation forecasting models by investigating and applying fundamental concepts from the social sciences. After extensive reviews of the literature in Phase I and the early part of Phase II, three concepts were selected for in-depth investigation. Lifestyle, which can be defined as how individuals and households allocate time to alternative activities such as work, in-home time, and recreation, has become increasingly prominent in travel behavior research. The emphasis on activities is also consistent with a stratification of travel by trip purpose. Life cycle, typically defined in terms of the ages of the adult members of a household and the number and ages of children, was also selected for investigation. Household structure is a closely related concept, especially relevant in light of the ongoing changing size and composition of households. The life cycle and household structure concepts suggest that the number of household members, a variable typically used in standard trip generation models, might not adequately capture the characteristics of households that affect travel demand. The standard urban transportation demand forecasting system consists of four components: trip generation, trip distribution, modal choice, and route assignment. In order to avoid duplication of other major research projects, and to use this project's resources in a cost-effective manner, the research team and the NCHRP advisory panel determined that enhancement of the trip generation models would be the major practical focus. Analyses were performed in three major areas. First, the effects of life cycle, household structure, and other sociodemographic variables on the allocation of time to specific activities by individuals were examined. Second, the usefulness of life cycle, household structure, and residential location characteristics in trip generation models was explored. Third, structural equation methods were used to analyze simultaneously the interactions among measures of mobility such as travel time, travel distance, and trip frequency.

Abstract: In the conventional evacuation planning process, evacuees are assigned to fixed destinations mainly on the basis of geographical proximity. However, the use of such prespecified destinations (an origin-destination table) almost always results in less-than-optimal evacuation efficiency because of uncertain road conditions, including traffic congestion, road blockage, and other hazards associated with the emergency. By relaxing the constraint of assigning evacuees to prespecified destinations, a one-destination evacuation (ODE) concept has the potential to improve evacuation efficiency greatly. To this end, a framework for the simultaneous optimization of evacuation traffic distribution and assignment is proposed. The ODE concept can be used to obtain an optimal destination and route assignment by solving a one-destination (1D) traffic assignment problem on a modified network representation. When tested for a countywide special event-based evacuation case study, the proposed 1D model presents substantial im...