David C. Novak

A Review of Current Practice in Network Disruption Analysis and an Assessment of the Ability to Account for Isolating Links in Transportation Networks

Abstract This paper presents a comprehensive review of the scholarly literature related to the field of network-disruption analysis. Research related to network disruption has progressed immensely since the late 1990s and now includes a wide variety of themes and approaches used to assess the impacts associated with a variety of disruptive events. Of particular relevance are those approaches which use repetitive link and/or node-removal methodologies to develop measures of network robustness or vulnerability (complementary concepts). More recently, various methods have begun to focus on the sequential application of equilibrium-based traffic assignments to measure the cost of a disruption to the network. It is crucial for these types of methods to handle the complexities of real-world transportation networks — one of which is the presence of isolating links in a network, which provide a single link to a particular region or subnetwork. A number of methods have attempted to deal with the problem of isolating links in different ways, but none has been ubiquitously successful. To develop a comprehensive and useful measure of transportation network robustness it is important to successfully address the issue of isolating network links.

A link-focused methodology for evaluating accessibility to emergency services

This paper considers the development of a new measure for evaluating accessibility to emergency services via a road network called critical closeness accessibility (CCA). CCA quantifies the relative importance of each link in a roadway network with respect to its system-wide contribution to emergency service accessibility and is based on the network science/graph theory concept of closeness. CCA is a link-focused measure that used to evaluate accessibility on a link-by-link basis and can be used for disconnected networks. We introduce a relative importance-based weighting approach for both origins and destinations that can be applied to different types of nodes including generic link endpoints that represent individual intersections and roadway segments in GIS-based roadway maps as well as to physical locations. CAA offers a unique approach for evaluating accessibility that accounts for the spatial distribution of emergency service locations, the topology of the road network, and the engineering characteristics of the road network such as road types, capacities, volumes, and travel speeds.

A traffic shaping model for optimizing network operations

The management of technology in multi-service computer networks, such as university networks, has become a challenge with the explosive growth of entertainment oriented peer-to-peer (P2P) traffic. Traffic shaping is one of the tools used to manage bandwidth to improve system performance by allocating bandwidth between P2P and non-peer-to-peer (NP2P) traffic. We present a model for traffic shaping and bandwidth management that considers the trade-offs from allocating different amounts of bandwidths for different application categories and use data from a university network. The current policy allocates varying bandwidths over the day to P2P and NP2P traffic to reflect the importance of not letting entertainment based traffic choke the network during the day time at the expense of the more important traffic, such as Web traffic. We highlight the difficulties in obtaining data in the form required for analysis, and the need to estimate demand for allocations not covered by current policy. We present a goal programming model for this estimation task. We also model the traffic shaping problem as a Markov decision process and develop an algorithm for determining the optimal bandwidth allocation to maximize the utility of all users. Finally we use a numerical example to illustrate our approach.

Managing blood inventory with multiple independent sources of supply

This paper focuses on the management of red blood cells (RBCs) by a large medical center within a regional blood exchange network. We provide both a theoretical and managerial contribution to the periodic-review fixed lifetime perishable inventory literature by considering multiple independent sources of supply. One source supplies blood via a typical standing order process. The other sources are smaller lower usage hospitals that randomly transfer blood to the medical center. Transferred blood is characterized by a much shorter average lifetime than blood supplied via standing order and introduces additional uncertainty into the inventory management process. We propose a solution approach that can be readily applied in practice and solve the multi-period cost minimization problem using a dynamic program. We provide numerical examples and demonstrate that our solution approach outperforms a corresponding base stock policy as well as the ordering policy that was actually used by the medical center.

Managing bandwidth allocations between competing recreational and non-recreational traffic on campus networks

Network performance is a serious concern faced by many campus network managers across the country. As demand for entertainment-based Peer-to-Peer (P2P) applications that involve the transfer of large audio and video files continues to grow, managers are faced with the increasingly difficult task of determining how much bandwidth should be allocated to these applications. Unrestricted P2P traffic has the potential to monopolize bandwidth and severely degrade network performance. University IT managers are placed in a particularly difficult position, because they must juggle demands for non-recreational traffic without severely restricting recreational use of the network. This paper discusses a solution for optimizing bandwidth allocations on a campus gateway Internet link.

Strategic Location of Satellite Salt Facilities for Roadway Snow and Ice Control

Roadway snow and ice control (RSIC) operations can account for as much as 10% of the annual budget of a states department of transportation (DOT) in the snowbelt of the United States. Important considerations for planning RSIC operations are the locations and quantities of surface treatment materials. This study examined the use of satellite salt facilities (SSFs) and developed a novel, real-world approach for locating SSFs. The paper demonstrates a method for ranking the effectiveness of individual SSFs in their reduction of the distance that vehicles must travel to reload salt. The approach is demonstrated with the federal aid roadway network for the state of Vermont, and a locally optimal SSF location is identified for each of the existing service territories in the state. The results of an informal survey of satellite salt-siting practices among snowbelt DOTs are also reported. A critical aspect to siting new SSFs is the ability to use existing right-of-way around Interstates; survey respondents noted the need to explore public–private partnerships with landowners adjacent to the state highway right-of-way who may be willing to sell or lease small portions of cleared land for use as SSFs. From the survey information, the study compared a smaller set of ready-to-use SSF locations (with adequate right-of-way) with the locally optimized SSF locations.