Theodore S. Glickman

Low Probability—High Consequence Considerations in Routing Hazardous Material Shipments

This paper is concerned with the development and analysis of a mathematical model for determining a route that attempts to reduce the risk of low probability---high consequence accidents related with the transportation of hazardous materials. The approach adopted considers trade-offs between the conditional expectation of a catastrophic outcome given that an accident has occurred, and more traditional measures of risk dealing with the expected value of the consequence and the accident probability on a selected path. More specifically, the problem we address involves finding a path that minimizes the conditional expectation objective value, subject to the expected value of the consequence being lesser than or equal to a specified value v , and the probability of an accident on the path being also constrained to be no more than some value (eta). The values v and (eta) are user-prescribed and could be prompted by the solution to the shortest path problems that minimize the respective corresponding linear risk functions. The proposed model is a discrete, fractional programming problem that is solved using a specialized branch-and-bound approach. A numerical example is provided for the sake of illustration, and some computational experience on randomly generated test cases is provided to study the effort required to solve this problem in different instances. The model is also tested using realistic data associated with a case concerned with routing hazardous materials through the roadways of Bethlehem, Pennsylvania. Data acquisition as well as algorithmic computational issues are discussed.

REROUTING RAILROAD SHIPMENTS OF HAZARDOUS MATERIALS TO AVOID POPULATED AREAS

Abstract The casualty risk due to hazardous material releases from railroad cars in the U.S. is estimated for a recent year. Approximate flow patterns of hazardous materials in that year are generated using a national network model. Alternative flow patterns representing population-avoidance rerouting policies are also generated, and some aggregate impacts are estimated with and without track upgrading. We find that population exposure can be reduced 25–50% by rerouting, at the cost of a 15–30% increase in traffic circuity. We also formulate and apply a risk model which shows that extensive routing changes can reduce casualties by about 50% but that extensive upgrading with or without rerouting can be even more effective. The effects on urban areas of the hypothetical changes are discussed, but financial impacts on the railroads are not addressed.

Large-scale network distribution of pooled empty freight cars over time, with limited substitution and equitable benefits

A set of models and procedures is described for finding the optimal distribution of empty freight cars owned by the railroads participating in a pooling agreement. A distinction is drawn between a system focus, in which the emphasis is on minimizing total cost, and a company focus, in which the benefits of the agreement to the individual railroads are emphasized. Limited car substitution is accounted for by combining interchange costs with distribution costs, and incorporating interchange possibilities and prohibitions into the network structure. Temporal variations in car supply and demand levels are also taken into account. A large-scale network algorithm is used in conjunction with decomposition to obtain solutions which show for a given time horizon how much equity can be achieved in the balance of savings among the railroads involved and at what cost. Results using actual operating data are reported.

Allocating Emergency Response Resources to Minimize Risk with Equity Considerations

SYNOPTIC ABSTRACT In this paper, we consider the problem of allocating certain available emergency response resources to mitigate risks that arise in the aftermath of a natural disaster, terrorist attack, or other unforeseen calamities. The resulting model formulation is a nonconvex program, for which we derive a tight linear programming relaxation. This relaxation is embedded within a specialized branch-and-bound procedure, and the proposed method is proven to converge to a global optimum. Various alternative partitioning strategies that could potentially be employed in the context of this branch-and-bound framework, while preserving the theoretical convergence property, are also explored. Computational results are reported for a hypothetical case scenario based on different parameter inputs and alternative branching strategies, and comparisons with the commercial software BARON as well as an ad-hoc intuitive method are presented.

GIS-Based Environmental Equity Analysis A Case Study of TRI Facilities in the Pittsburgh Area

The issue of environmental equity has received considerable media attention in the United States recently, generating a flurry of activity among members of the environmental community, including the U.S. Environmental Protection Agency and the leading environmental groups. Many studies have investigated the existence of inequities in the distribution of noxious, toxic or otherwise unwanted facilities, and many more studies are ongoing. Most of these studies have been conducted at a national or regional scale, and involve comparing the socioeconomic and demographic characteristics of host and non-host communities. The distribution of facilities is considered inequitable if the percentage of minorities is disproportionately higher or the socioeconomic status is disproportionately lower in the host communities.

Biconvex Models and Algorithms for Risk Management Problems

SYNOPTIC ABSTRACTThis paper deals with the risk management problem of determining an optimal mix of available strategies for attenuating accident probabilities as well as the ensuing consequences of harmful events, so as to minimize the total risk associated with a given set of risky activities, subject to budgetary and operational constraints. The problem is modeled as a biconvex programming problem that happens to be nonconvex. For the case of a single risk, we propose an outer-linearization scheme that is proven to converge to an optimal solution. By projecting the problem onto the bivariate probability-consequence attenuation space, an alternative graphical solution scheme is also proposed that enables the decision maker to interact subjectively with the process. These models and concepts are extended to the multiple risk situation. Finally, we also provide and discuss alternative models that consider certain strategic issues related to acceptable risk, equitable risk, and the incorporation of uncerta...

RISK ANALYSIS OF RAILROAD FREIGHT TRANSPORTATION DISASTERS

Abstract A risk analysis is performed of the potential for disastrous freight train derailment accidents in the U.S. involving the release of bulk shipments of hazardous materials. The risk is expressed as the probability of any number of fatalities in each accident and as the probability of any number of fatalities per year. Models for these risk profiles are formulated and then restructured to permit computer calculations using numerical methods. Particular attention is given to the computation of low probabilities associated with high consequences. Taking into account the impacts on both the general population and on-scene professional personnel, the risk is found to be lower than for other familiar safety problems.

Parametric cost-benefit analysis applied to underwater pipeline safety

Policy alternatives must often be evaluated without the benefit of experimentation to determine the effectiveness of each one. A parametric approach to dealing with this problem is presented for the case of deciding on the appropriate degree of deregulation, if any, for the use of signs to prevent accidents involving damage to underwater pipelines. The information obtained demonstrates whether experimentation would have been advantageous and, if so, how the policy conclusions would have been affected.