George F. List

Modeling and Analysis for Hazardous Materials Transportation: Risk Analysis, Routing/Scheduling and Facility Location

We survey research on hazardous materials transportation in the areas of risk analysis, routing/scheduling and facility location. Our focus is primarily on work done since 1980, and on research which is methodological rather than empirical. We also limit our focus to transport by land-based vehicles (truck and rail), excluding pipeline, air and maritime movements. The review traces the evolution of models from single-criterion optimizations to multiobjective analyses, and highlights the emerging direction of dealing explicitly with distributions of outcomes, rather than simply optimizing expected values. We also indicate examples of work which integrate risk analysis with routing, and routing with facility location. We conclude with a discussion of several aspects of hazardous materials transportation which offer important challenges for further research.

AN INTEGRATED NETWORK PLANAR MULTIOBJECTIVE MODEL FOR ROUTING AND SITING FOR HAZARDOUS MATERIALS AND WASTES

Dealing with hazardous materials and wastes has become a problem of major concern for countries throughout the world. This paper presents a model useful in making routing decision, for either material or waste shipments, and siting decisions for waste treatment facilities. Risk, cost, and risk equity are considered jointly in a multiobjective framework. Costs are treated as link attributes while risks, from both transport and treatment, are zonal attributes, pertaining to nonoverlapping geographic areas spread out over the plane. Risks accrue within these zones, due to shipments crossing nearby links or wastes being processed, stored or disposed of at nearby treatment facilities. Total risk is the sum of the zonal risks. Equity is measured as the maximum zonal risk per unit population. Shippers will find the model useful in optimizing their logistics plans. Government agencies will find it helpful in determining how regulations should be set to obtain publicly desirable routing and siting patterns. The model is described in detail and applied in simplified form to an illustrative problem.

Modeling traffic signal control using Petri nets

This paper focuses on the use of Petri nets (PN) to model the control of signalized intersections. The application of PN to an eight-phase traffic signal controller is illustrated. Structural analysis of the control PN model is performed to demonstrate how the model enforces the traffic operation safety rules. This is followed by a discussion of why this modeling tool has future value as the use of more advanced control strategies continue to expand.

Robust optimization for fleet planning under uncertainty

We create a formulation and a solution procedure for fleet sizing under uncertainty in future demands and operating conditions. The formulation focuses on robust optimization, using a partial moment measure of risk. This risk measure is incorporated into the expected recourse function of a two-stage stochastic programming formulation, and stochastic decomposition is used as a solution procedure. A numerical example illustrates the importance of including uncertainty in the fleet sizing problem formulation, and the nature of the fundamental tradeoff between acquiring more vehicles and accepting the risk of potentially high costs if insufficient resources are available.

The Application of Petri Nets to the Modeling, Analysis and Control of Intelligent Urban Traffic Networks

This paper focuses on the development of Petri net models and tools for the control and performance analysis of signalized traffic intersections and networks of connected intersections. The potential for Petri nets as a single representation for multiple tools for addressing traffic network problems is discussed. These tools can contribute to the modeling, analysis, performance evaluation, control design and direct control code generation for urban traffic network control. A colored Petri net model of an urban traffic network for the purpose of performance evaluation is presented and discussed. The subnets for the network, the intersections, the external traffic inputs and control are each described. A six intersection urban network example is given to illustrate the subnets and a model step-through is given to show how the subnets work together. This net is used as the input to a simulation using POSES to evaluate the performance of various control strategies. Runs are made using different control strategies and statistics on intersection queue lengths and wait times are given. Conclusions and future research directions are presented.

Routing and emergency-response-team siting for high-level radioactive waste shipments

Route choice and emergency response team siting are both important facets of any high-level radioactive waste shipment campaign. These two sets of decisions are clearly related, and both involve multiple objectives. This paper describes a methodology for making these decisions jointly, in a logical and sequential fashion, and illustrates the technique using preliminary estimates of shipments to be made to the Waste Isolation Pilot Project facility.

Factors Affecting Minimum Number of Probes Required for Reliable Estimation of Travel Time

Using probe vehicles rather than other detection technologies has great value, especially when travel time information is sought in a transportation network. Even though probes enable direct measurement of travel times across links, the quality or reliability of a system state estimate based on such measurements depends heavily on the number of probe observations across time and space. Clearly, it is important to know what level of travel time reliability can be achieved from a given number of probes. It is equally important to find ways (other than increasing the sample size of probes) of improving the reliability in the travel time estimate. This paper provides two new perspectives on those topics. First, the probe estimation problem is formulated in the context of estimating travel times. Second, a method is introduced to create a virtual network by inserting dummy nodes in the midpoints of links to enhance the ability to estimate travel times further in a way that is more consistent with the processing that vehicles receive. Numerical experiments are presented to illustrate the value of those ideas.

Logistics planning under uncertainty for disposition of radioactive wastes

The US Department of Energy (DOE) faces an enormous environmental remediation challenge involving highly radioactive wastes at former weapons production facilities. The purpose of this analysis is to focus on equipment acquisition and fleet sizing issues related to transportation of wastes from remediation sites to disposal sites. Planning for the transportation of these wastes must be done with recognition of important uncertainties related to overall quantities of waste to be moved, the rate at which the wastes will be prepared for transport, and the certification of suitable transportation containers for use in the effort. However, deadlines for completion of the effort have already been set by the political process, without much regard for these uncertainties. To address this fleet sizing problem, we have created a robust optimization model that focuses on equipment investment decisions. Through this robust optimization, we illustrate how modeling can be used to explore the effects of uncertainty on the equipment acquisition strategy. The disposition of radioactive wastes from DOE sites is an important illustration of a category of problems where equipment investments must be made under conditions of considerable uncertainty. The methodology illustrated in this paper can be applied to this general class of problems.

Multiobjective Policy Analysis of Hazardous Materials Routing

This paper is a case study in developing policy options for regulating hazardous materials truck transportation routes. The case study setting is the Capital District of New York State, and the analysis is directed at hazardous waste shipments entering the area and bound for a treatment site within the area. The analysis is based on using a multiobjective routing model to provide a set of nondominated routing alternatives, from which various policy options are developed. The conclusions are that such analysis is feasible and tractable, and that policies based on a few selected link restrictions can provide substantial public risk reduction without excessive micromanagement of carriers.

TOWARD OPTIMAL SKETCH-LEVEL TRANSIT SERVICE PLANS

A model and methodology are presented for preparing optimal sketch-level service plans for passenger systems that operate vehicles, singly or in multiple units, over a fixed network on a fixed schedule. The model uses transshipment equations to develop optimal vehicle flows, by link and time period, in response to passenger flows, service frequency requirements, line segment capacities, system fleet size, and storage node capacities. Frequency variables are used to represent the flows which reduces the need for integer variables and reduces solution times. It also makes possible the use of the model when many service alternatives are to be evaluated in a short period of time. In addition, the models explicit treatment of equipment balancing results in an easy-to-understand solution with cost and resource estimates that can be traced clearly to the underlying vehicle movements.