Fifty-one infants born to women employed at two capacitor manufacturing facilities with a history of high exposure to polychlorinated biphenyls (PCBs) had a mean birthweight of 153 grams less than that of 337 infants born to women who had worked in low-exposure areas (90 per cent confidence interval, -286 to -20 g); mean gestational age was 6.6 days shorter in the high-exposure infants (90 per cent CI, -10.3 to -2.9 days). After adjusting for gestational age, the difference in birthweight was markedly reduced, indicating that the observed reduction in birthweight was due mainly to shortening of gestational age in the high-exposure group. (Am J
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.
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 (1 D) traffic assignment problem on a modified network representation. When tested for a countywide special event–based evacuation case study, the proposed 1 D model presents substantial improvement over the conventional multiple-destination ( nD) model and can potentially reduce overall evacuation time by more than 60%. More important, this framework can be easily implemented and its efficiency enhanced simply by instructing evacuees to head for destinations resulting from the 1 D simulations run beforehand.
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