A Survey of Operations Research Models and Applications in Homeland Security

informs       ®

Vol. 36, No. 6, November–December 2006, pp. 514–529                                                          doi 10.1287/inte.1060.0253
issn 0092-2102  eissn 1526-551X  06  3606  0514                                                                   © 2006 INFORMS

           A Survey of Operations Research Models and
               Applications in Homeland Security
                       P. Daniel Wright, Matthew J. Liberatore, Robert L. Nydick
              Department of Decision and Information Technologies, Villanova University, Villanova, Pennsylvania 19085
                    {daniel.wright@villanova.edu, matthew.liberatore@villanova.edu, robert.nydick@villanova.edu}

      Operations research has had a long and distinguished history of work in emergency preparedness and response,
      airline security, transportation of hazardous materials, and threat and vulnerability analysis. Since the attacks
      of September 11, 2001 and the formation of the US Department of Homeland Security, these topics have been
      gathered under the broad umbrella of homeland security. In addition, other areas of OR applications in home-
      land security are evolving, such as border and port security, cyber security, and critical infrastructure protection.
      The opportunities for operations researchers to contribute to homeland security remain numerous.
      Key words: government: agencies; planning: government, homeland security.
      History: This paper was refereed.

S   ince September 11, 2001, the term homeland secu-
    rity has entered the vernacular of the United States
and of countries around the world. In the US, it is
                                                                      form it, the government reorganized several agencies
                                                                      and programs and evaluated its existing security
                                                                      efforts (National Commission on Terrorist Attacks
defined as “a concerted national effort to prevent terrorist           upon the United States 2004). It put several existing
attacks within the United States, reduce America’s vulner-            agencies under one domain to unite their efforts to
ability to terrorism, and minimize the damage and recover             better protect the country. The department is orga-
from attacks that do occur” (Office of Homeland Secu-                  nized into five directorates: border and transportation
rity 2002, p. 2). Despite the recency of the term, for                security, emergency preparedness and response, sci-
decades the operations research community has been                    ence and technology, information analysis and infras-
exploring issues that we now classify under home-                     tructure protection, and management. Each direc-
land security. As far back as 1960, OR researchers                    torate contains several agencies that were formerly
were working on such issues. At the seventh inter-                    housed in different departments of the federal gov-
national meeting of the Institute of Management Sci-                  ernment. For instance, the border and transportation
ences (TIMS), Wood (1961) highlighted US vulnera-                     security directorate now includes the US Customs
                                                                      Service, the Transportation Security Administration,
bility and potential responses to nuclear attack. He
                                                                      and the Animal and Plant Health Inspection Service,
called on the OR community to develop techniques
                                                                      which were originally the responsibility of the Trea-
and programs to maintain freedom. Since that time,
                                                                      sury, Justice, and Agriculture Departments, respec-
operations researchers have focused on such top-
                                                                      tively. For all of its directorates, the Department of
ics as emergency preparedness and response, airline
                                                                      Homeland Security states its mission as follows:
security, hazardous material transportation, and cyber
                                                                        We will lead the unified national effort to secure Amer-
security. All of these areas are increasingly important
                                                                        ica. We will prevent and deter terrorist attacks and protect
to homeland security. While they have done much,                        against and respond to threats and hazards to the nation. We
operations researchers still have rich opportunities                    will ensure safe and secure borders, welcome lawful immi-
available.                                                              grants and visitors, and promote the free-flow of commerce
   The US Department of Homeland Security (DHS),                        (Department of Homeland Security 2005).
formed in October 2001, has a broad set of responsi-                  The mission is reinforced by several strategic goals,
bilities that contribute to securing the homeland. To                 including awareness, prevention, protection, response,
Wright, Liberatore, and Nydick: Survey of Operations Research Models and Applications in Homeland Security
Interfaces 36(6), pp. 514–529, © 2006 INFORMS                                                                                                  515

recovery, service, and organizational excellence. Both
the mission and the strategic goals of the DHS pro-                    Countermeasures portfolios
                                                                         Biological                   Reduce the probability and consequences
vide exciting opportunities for operations research.
                                                                                                        of a biological attack
                                                                         Chemical                     Reduce the nation’s vulnerability to chemical
Literature Framework                                                     Radiological and nuclear     Develop and deploy techniques for detection
Many research agendas contribute directly or indi-                                                      of radiological materials
                                                                         High explosives              Provide the concepts, technologies, systems
rectly to homeland security. Organizing the litera-                                                     analysis, and procedures to interdict
ture concerning homeland security is challenging.                                                       terrorists’ use of explosives
Research in homeland security falls under the sci-                     Component-support portfolios
ence and technology directorate, which is the pri-                       Border and transportation    Prevent the entry of terrorists while ensuring
mary research-and-development arm of the DHS. It                            security                     efficient flow of traffic and commerce
                                                                         Critical infrastructure      Develop tools to anticipate, identify, and
describes three main research areas that contribute to                      protection                   assess the risks in the nation’s critical
the state of the art in homeland security: (1) coun-                                                     infrastructure
termeasures portfolios, (2) component-support portfo-                    Cyber security               Research, develop, test, and evaluate
                                                                                                         activities for improving cyber security
lios, and (3) cross-cutting portfolios. The science and                  Emergency preparedness       Plan for, prevent, respond to, and recover
technology directorate conducts and funds research in                      and response                  from natural and man-made disasters and
all of these portfolios. A few authors have reported on                                                  terrorism
                                                                         Threat analysis              Evaluate extensive and diverse threat
the impact of science and technology, including infor-                                                   information
mation technology, on terrorism response (Branscomb
and Klausner 2003, Hennessy et al. 2003).                              Table 1: The countermeasures and component-support portfolios of the
                                                                       Department of Homeland Security research portfolios protect against
   The main purpose of the countermeasures port-
                                                                       weapons of mass destruction and support department components,
folio is to protect the US from weapons of mass                        respectively (adapted from www.dhs.gov).
destruction. Research in this area concerns vulnerabil-
ities and risks surrounding biological, chemical, radi-
ological, and nuclear weapons, and high explosives.                    In addition, they offer the greatest opportunity for
The research invites collaboration between operations                  contributions combining OR and homeland security
researchers and physical scientists.                                   (Table 1).
   The component-support portfolios focus on increas-                    We sought articles on OR and homeland security
ing the capabilities of DHS components and help-                       throughout the world published in academic journals.
ing them to secure the homeland. The components                        While some military research concerns homeland
include border and transportation security, critical                   security, it does not fall under the US Department of
infrastructure protection, cyber security, emergency                   Homeland Security and its research agenda. Jaiswal
preparedness and response, threat and vulnerability                    (1997) reviewed military OR models and techniques,
testing and assessment, the US Coast Guard, and the                    and Miser (1998), Bonder (2002), and Hughes (2002)
US Secret Service. In this portfolio, OR has the great-                discussed the historical impact of OR on the military.
est history and perhaps the most potential to improve                    Operations researchers have contributed in many
homeland security.                                                     ways to homeland security. We use the DHS science
   The cross-cutting portfolios focus on other vulner-                 and technology framework to discuss previous work.
abilities and risks that extend across the countermea-
sures and component support portfolios. They include
emerging threats, rapid prototyping, standards, and                    Countermeasures Portfolios
university programs. Although OR could contribute                      Countermeasure efforts address the risks of biolog-
to cross-cutting, most previous work is better catego-                 ical, chemical, radiological, and nuclear weapons,
rized in the other two portfolios.                                     and high explosives. The OR community has studied
   We focus on the first two portfolios because most                    problems in this area with notable results. Sullivan
OR-related research has fallen in those portfolios.                    and Perry (2004) developed a useful framework for
Wright, Liberatore, and Nydick: Survey of Operations Research Models and Applications in Homeland Security
516                                                                                         Interfaces 36(6), pp. 514–529, © 2006 INFORMS

categorizing terrorist groups’ development of chem-               Border and Transportation Security
ical, biological, radiological, and nuclear weapons.              Border and transportation security problems have
They investigated three classification approaches, in-             been and continue to be of great interest to opera-
cluding a heuristic pattern-recognition method, clas-             tions researchers particularly because these types of
sification trees, and discriminant analysis.                       problems are a good match for OR techniques. Within
   Dyer et al. (1998) and Butler et al. (2005) addressed          the DHS framework, border security includes improv-
the problem of disposing of weapons-grade pluto-                  ing the security of the nation’s borders to prevent the
nium. Dyer et al. (1998) used multiple attribute utility          entry of terrorists, criminals, and illegal aliens while
theory (MAUT) to develop a hierarchy of objectives,               maintaining the safe flow of commerce and travelers.
to evaluate 13 alternatives, and to conduct sensitiv-             Transportation security includes the safety of airlines,
ity analyses. Butler et al. (2005) used MAUT to help              railroads, ships, and trucks.
the US and Russia to evaluate alternatives for dispos-
ing of stockpiles of weapons-grade plutonium. They                Border Security
recommended converting the plutonium for use as                   Papers on border security are just beginning to appear.
fuel in nuclear power plants. Munera et al. (1997)                Wein and Baveja (2005) studied two programs: the US
described the safety and security concerns posed by               visitor program and the immigrant-status-indicator-
transporting highly enriched uranium used in nuclear              technology program. These two programs aim to re-
reactors. They used stochastic dominance to evaluate              duce visa fraud and detect the entry of watch-listed
the risks of road and air alternatives.                           criminals and suspected terrorists into the United
   Hupert et al. (2002) used discrete-event simulation            States. Using a game-theoretic model, the authors
to determine staffing levels for entry, triage, medi-              show that the quality of fingerprint images is impor-
cal evaluation, and drug dispensing in a hypothetical             tant to detection probability and thus system perform-
distribution center under conditions of low, medium,              ance. They discussed fingerprint-scanning strategies
and high bioterrorism attack. Craft et al. (2005) cre-            that help counter terrorists’ attempts to minimize
ated a series of differential equations to determine the          detection.
potential number of deaths from an aerosol bioterror
attack. Their method included an atmospheric-release              Airline Security
model, a spatial array of biosensors, a dose-response             After the hijacking of commercial airlines that led to
model, a disease-progression model, and an antibi-                the catastrophic events of September 11th, 2001, the
otics model with a queue. Kaplan et al. (2002, 2003)              US Federal Aviation Administration and Transporta-
also used differential equations to study response to             tion Security Administration tightened security mea-
a smallpox attack. Walden and Kaplan (2004) used a                sures at airports around the country. Barnett (2004)
Bayesian approach to estimate the size and time of                described a dynamic computer system that uses prob-
an anthrax attack to determine the number of persons              ability models and data-mining techniques to clas-
who might require medical care. Wein et al. (2003) also           sify airline-passenger threats. However, many airline
modeled emergency response to an anthrax attack.                  security issues still need attention (Turney et al. 2004).
   Jenkins (2000) used integer programming to iden-               Coincidentally many OR researchers addressed air-
tify a small subset of oil spills that are similar to all         line security before 2001, focusing primarily on scan-
potential categories of spills to predict the type of pol-        ning passengers or baggage. Gilliam (1979) employed
lutant a terrorist group might use. Buckeridge et al.             queuing theory for passenger screening. Kobza and
(2005) classified bioterrorism outbreak algorithms and             Jacobson (1997) discussed the design of access secu-
found that spatial and other covariate information can            rity systems in airports. They developed performance
improve measures for detecting and evaluating out-                measures based on the probabilities of false alarms
breaks. Stuart and Wilkening (2005) used first- and                and false clears that determine the effectiveness of
second-order catastrophic decay models to study the               single-device and multiple-device security systems.
impact of degradation of biological-weapons agents                Jacobson et al. (2000) developed a sampling procedure
leaked into the environment.                                      that estimates false-alarm and false-clear probabilities.
Wright, Liberatore, and Nydick: Survey of Operations Research Models and Applications in Homeland Security
Interfaces 36(6), pp. 514–529, © 2006 INFORMS                                                                                517

Kobza and Jacobson (1996) studied security-system                      identified US ports as vulnerable and as very attrac-
design by addressing the dependence between the                        tive targets for terrorists. Lewis et al. (2003) for-
responses of security devices in multiple-device sys-                  mulated a shortest-path model for container-security
tems. These articles could help managers to improve                    operations at US seaports. They identified and ana-
decisions on airport security systems and are some-                    lyzed trade-offs between the number of containers
what generalizable to other types of security systems.                 inspected and the costs of delayed vessel departures.
   Jacobson et al. (2001) described aviation security as                  The US railway system must be protected to pre-
a knapsack problem and proposed a model that deter-                    vent the sabotage of passenger or cargo trains and to
mines how to minimize the false-alarm rate of a given                  prevent terrorists’ gaining control of hazardous ship-
security system. Barnett et al. (2001) conducted an                    ments. Glickman and Rosenfield (1984) formulated
experiment to evaluate the costs of bag-match strate-                  models to evaluate the risks associated with train
gies to the airlines and to the passengers in terms of                 derailments and the release of hazardous materials,
monetary cost and passenger delay. Jacobson et al.                     issues that could become important in the event of a
(2003) discussed three important performance mea-                      terrorist attack.
sures of baggage screening: the number of passen-
                                                                       Truck Security
gers on flights with unscanned bags, the number of
                                                                       The main issue for the trucking system is the trans-
flight segments with unscanned bags, and the total
                                                                       portation of hazardous materials. Many of the arti-
number of unscanned bags. Using examples based on
                                                                       cles in the OR literature on transporting hazardous
real data, they showed how a greedy algorithm can
                                                                       materials do not focus on homeland security, that is,
minimize the performance measures. Jacobson et al.
                                                                       preventing terrorists from hijacking these materials
(2005) discussed the optimization of the first two mea-
                                                                       and using them in weapons. The literature focuses
sures through the allocation and utilization of screen-
                                                                       on two related issues: routing vehicles and analyzing
ing devices.
                                                                       risk. Routing hazardous vehicles involves determin-
   The cost of airline security concerns airports and
                                                                       ing what paths vehicles should take to minimize pop-
commercial airlines. Candalino et al. (2004) discussed
                                                                       ulation exposure in the event of an accident. Many
a software system for screening checked baggage that
                                                                       authors have developed algorithms and heuristics for
uses data on purchase and operating costs to allocate
                                                                       solving various cases of the routing problem (Batta
security devices around the country. They proposed
                                                                       and Chiu 1986, 1988; Berman et al. 2000; Beroggi
an alternative cost function that includes indirect
                                                                       and Wallace 1994, 2005; Erkut and Ingolfsson 2000;
costs related to scanning errors. Virta et al. (2003) con-
                                                                       Giannikos 1998; Jin et al. 1996; Karkazis and Boffey
sidered the direct and indirect costs of scanning poli-
                                                                       1995; Lindner-Dutton et al. 1991; List and Turnquist
cies based on the passengers selected by the screening
                                                                       1998; van Steen 1987; Zografos and Androutsopoulos
                                                                       2004). Related to the routing problem are methods
   Long customer waits are an important issue for air-
                                                                       for treating and analyzing risk (Erkut and Ingolfsson
ports who want to keep passengers happy and reduce
                                                                       2005, Erkut and Verter 1998, Gopalan et al. 1990, Kara
congestion. Leone and Liu (2003) developed a sim-
                                                                       et al. 2003, Raj and Pritchard 2000).
ulation model that investigates passenger traffic and
throughput rates for scanning devices. They discov-
ered that the machines’ throughput rates were far                      Critical Infrastructure Protection
lower than their advertised scan rates.                                To protect the critical infrastructure, analysts develop
   As policies and scanning technologies change, oper-                 tools to anticipate, identify, and assess the risks in the
ations researchers should find further opportunities                    nation’s critical infrastructure and attempt to reduce
in airline security.                                                   the risks and the consequences of an attack. Potential
                                                                       infrastructure targets include agriculture and food,
Port and Rail Security                                                 banking and finance, dams, high-profile events, infor-
Currently, little operations research deals with the                   mation systems, public health, national monuments,
security of ports and railroads. Harrald et al. (2004)                 nuclear power plants, and water systems.
Wright, Liberatore, and Nydick: Survey of Operations Research Models and Applications in Homeland Security
518                                                                                         Interfaces 36(6), pp. 514–529, © 2006 INFORMS

   Apostolakis and Lemon (2005) used MAUT to pri-                 a chemical plant failure and showed that they could
oritize the vulnerabilities in an infrastructure that they        greatly improve risk assessment.
modeled using interconnected diagraphs and applied                   Chowdhury et al. (1999) used linear programming
graph theory to identify candidate scenarios. Brown               to limit the availability of confidential information
et al. (2004) applied simulation to study the impacts of          in a database while providing access to those who
disruptions and used risk analysis to assess infrastruc-          need it. They developed two transportation flow algo-
ture interdependencies. Their purpose was to iden-                rithms that are computationally efficient and insight-
tify infrastructure risks and ways to reduce them.                ful. Muralidhar et al. (1999) developed a model
Baskerville and Portougal (2003) developed a possibil-            to explain how to use data-perturbation methods
ity model that suggests that, during an optimal length            to protect information from unwanted access while
of time, the possibility of attack on information sys-            allowing maximum access to genuine inquiries and
tem infrastructures is very low.                                  maintaining the relationships between attributes.
   The risk associated with major utilities, such as
water systems, is important to homeland security                  Emergency Preparedness and Response
(Grigg 2003). Zografos et al. (1998) developed a data-            Emergency preparedness and response include such
management module, a vehicle-monitoring and com-                  topics as planning for, preventing, responding to,
munications module, and a modeling module and                     and recovering from natural disasters and terrorism.
applied them to an emergency-repair operation for                 Larson (2004, 2006) reviewed the literature on police,
an electric utility company. They used a combined                 fire, and emergency medical services, and provided
optimization and simulation approach to minimize                  some coverage of hazardous materials, bioterrorism,
service unavailability. Salmeron et al. (2004) devel-             and private-sector response to emergencies. The liter-
oped a max-min model to help determine weaknesses                 ature can be categorized into (1) early work, (2) loca-
in the electric grid to prepare for terrorist attacks.            tion and resource allocation, (3) evacuation models,
Through decomposition, they solved the problem                    and (4) disaster planning and response.
with a heuristic on two test systems.
                                                                  Early Work
                                                                  Green and Kolesar (2004) described a number of
Cyber Security                                                    papers on emergency-response systems. Much of the
Research in cyber security helps prevent, protect                 OR work on managing emergency services originated
against, detect, respond to, and recover from large-              with the New York City–Rand Institute. Its work with
scale cyber attacks on the information infrastructure.            the New York City Fire Department included a sim-
Although many studies concern network security, few               ulation model of firefighting operations (Carter and
can be considered operations research. Krings and                 Ignall 1970); queuing models of fire company avail-
Azadmanesh (2005) developed a model for trans-                    ability (Carter et al. 1972); the “square root law”
forming security and survivability applications so                for the location of fire companies based on response
that they can be solved with graph and schedul-                   distance, with a response time-distance function to
ing algorithms. Chen et al. (2005) explained how                  predict response time (developed by Kolesar and
shared networks and the Internet have focused inter-              Blum 1973 and applied by Rider 1976); an empiri-
est on IT security, particularly intrusion detection.             cal Bayes approach to alarm forecasting (Carter and
They used data-mining methods (artificial neural                   Rolph 1974); a stochastically-based integer linear pro-
networks and support vector machine) to identify                  gramming model and a heuristic algorithm for fire
potential intrusions. Abouzakhar and Manson (2002)                company relocation (Kolesar and Walker 1974); a set
addressed network security using two intelligent                  covering approach for locating two types of lad-
fuzzy agents to respond to denial-of-service attacks.             der fire trucks (Walker 1974); heuristics for identi-
Shindo et al. (2000) generated fault-tree and event-tree          fying high-priority alarm boxes (Ignall et al. 1975);
structures between a computer-network access point                Markovian decision models of initial dispatch of fire
and a process plant. They applied their analysis to               companies (Ignall et al. 1982, Swersey 1982); and a
Wright, Liberatore, and Nydick: Survey of Operations Research Models and Applications in Homeland Security
Interfaces 36(6), pp. 514–529, © 2006 INFORMS                                                                            519

book pulling together the accumulated work on fire                         Eaton et al. (1985) applied the MCLP model in
deployment analysis (Walker et al. 1979) under sup-                    Austin, Texas when EMS officials sought to improve
port from the US Department of Housing and Urban                       operating efficiency. Saccomanno and Allen (1988)
Development (HUD).                                                     used a modified MCLP algorithm to locate emer-
   The New York City–Rand Institute’s work with the                    gency response capability for potential spills of dan-
New York Police Department included work on de-                        gerous goods on a road network. Belardo et al. (1984b)
ployment related to the 911 emergency telephone sys-                   extended the MCLP to locate oil-spill-response equip-
tem (Larson 1972, 2002); scheduling patrol cars using                  ment on Long Island Sound. Chung (1986) described
queuing and linear programming (Kolesar et al. 1975);                  other applications of the MCLP.
and the patrol car allocation model (PCAM) based                          Hogan and ReVelle (1986) modified set covering
on queuing and linear programming (Chaiken and                         models to maximize the percentage of the population
Dormont 1978a, b). The multicar dispatch queuing                       that receives backup coverage. Pirkul and Schilling
model (Green 1984) was later incorporated into a                       (1988) developed a backup coverage model for facil-
revised version of PCAM (Green and Kolesar 1989)                       ities with limited workloads or capacities. Batta and
and applied to the proposed mergers of police and                      Mannur (1990) extended the set covering models
fire departments in several cities (Chelst 1988, 1990).                 to include some demand points requiring responses
Chaiken and Larson (1972) reviewed methods for                         from multiple units (for example, fire trucks or ambu-
allocating emergency units (vehicles). Chaiken (1978)                  lances).
described six models (including PCAM) developed                           Church et al. (1991) formulated a bicritera max-
with HUD support for fire and police operations and                     imal covering location model that maximizes the
the challenges of implementing them.                                   demand covered within the maximal distance and
Location and Resource Allocation                                       also minimizes the distance traveled from the uncov-
The early literature on locating emergency service                     ered demand to the nearest facility. Schilling et al.
facilities is based on the location set covering prob-                 (1979) developed the tandem equipment allocation
lem (LSCP) formulated by Toregas et al. (1971). In                     model (TEAM) and the facility location, equip-
this problem, a population is served or covered when                   ment, and emplacement technique (FLEET) model
a facility is located within an acceptable service dis-                to allocate equipment with varying capabilities and
tance. The objective is to minimize the number of                      demands. The FLEET model has been effectively
facilities while covering all demand points. Walker                    applied to locate fire stations and allocate equipment.
(1974) applied the LSCP to the location of ladder                      With some modifications, Tavakoli and Lightner
trucks in the boroughs of New York City. Plane and                     (2004) applied Bianchi and Church’s (1988) multi-
Hendrick (1977) applied the LSCP to the location of                    ple coverage, one-unit FLEET model (MOFLEET)
fire companies in Denver, Colorado. Daskin and Stern                    to Cumberland County, North Carolina’s emergency
(1981) extended the LSCP to address multiple cover-                    medical services (EMS) system.
age of demand nodes.                                                      Current and O’Kelly (1992) applied covering mod-
  The maximal covering location problem (MCLP)                         els to locate emergency warning sirens in a mid-
developed by Church and ReVelle (1974) relaxes the                     western city. Building on covering-model research,
LSCP’s requirement that all demand nodes are cov-                      Akella et al. (2005) addressed the problem of locating
ered. The MCLP seeks to maximize the total pop-                        cellular base stations and allocating channels, while
ulation served within a maximum service distance,                      explicitly considering emergency coverage of areas
given a fixed number of facilities. Because Church                      known for vehicle crashes and sites prone to potential
and ReVelle leave some population uncovered, they                      enemy attacks. The Lagrangean heuristic performed
include mandatory closeness constraints in their for-                  very well on test problems and in rural Erie County,
mulation. The MCLP is related to the p-median prob-                    New York.
lem (Hakimi 1964), which seeks to locate p facilities                     Several authors have developed optimization mod-
to minimize total demand-weighted travel distances                     els that include stochastic elements. Daskin (1983)
between demands and facilities.                                        developed the maximal expected coverage location
Wright, Liberatore, and Nydick: Survey of Operations Research Models and Applications in Homeland Security
520                                                                                        Interfaces 36(6), pp. 514–529, © 2006 INFORMS

model (MECLM), which seeks to locate emergency                   in the ambulance deployment method CALL (com-
vehicles to maximize the expected coverage area,                 puterized ambulance location logic), which located
even when multiple vehicles are in use. Batta et al.             ambulances to minimize mean response time. CALL
(1989) offered an extended version of MECLM. They                was successfully applied in central Los Angeles to
assumed that the probability that a randomly cho-                locate firehouses and in Melbourne, Australia to
sen vehicle is busy is independent of any other vehi-            plan an emergency ambulance system. Later CALL
cle in use. ReVelle and Hogan (1989) proposed a                  was combined with a contiguous zone search rou-
variation of MECLM called the maximum availabil-                 tine (CZSR) that uses an existing database on inter-
ity location model (MALM) in which each constraint               zone travel times to locate ambulances in Austin,
guarantees that the probability that a demand point              Texas (Fitzsimmons and Srikar 1982). Swoveland et al.
receives service within an acceptable time is no less            (1973) used simulation coupled with optimization to
than a required value. In these latter two models, the           locate ambulances in Vancouver, Canada.
analysts estimated probabilities that vehicles are busy
in advance. Ball and Lin (1993) developed a model                Evacuation Models
similar to MALM except that they directly model                  Researchers have developed optimization, queuing,
the source of the randomness. Goldberg and Paz                   and simulation models to plan emergency evacua-
(1991) developed an optimization model that seeks to             tions of buildings and areas. Most of such work relies
maximize the expected number of emergency callers                on queuing or simulation, although some uses opti-
reached within a specified time.                                  mization. Chalmet et al. (1982) applied transshipment
   Analytical queuing models have been used to eval-             and dynamic network optimization models to plan-
uate the performance of emergency service systems.               ning the evacuation of large buildings. They applied
In his hypercube model (1974, 1975, 2001), Larson                the models to the evacuation of 322 people from an
characterizes the operation of an emergency service              11-story building with four elevators and two stair-
system as a multiserver queuing system in which                  wells and compared the results with an observed
the states correspond to all combinations of servers             evacuation to reveal possible improvements.
busy and idle. This model provides a set of output                  Smith and Towsley (1981) applied analytical queu-
measures, such as vehicle utilization and average                ing network models to evacuating buildings using
travel time, and has been used to deploy ambu-                   several examples. They modeled the buildings as hier-
lances and police cars in various cities (Brandeau and           archical queuing networks. Talebi and Smith (1985)
Larson 1986, Larson and Rich 1987). Extensions in-               modeled the evacuation of a hospital as a finite closed
clude improving the accuracy of the model’s output               queuing network model using mean-value analy-
measures by allowing the service rates to be server              sis. Bakuli and Smith (1991, 1996; Smith 1991) used
dependent (Halpern 1977), estimating the probability             state-dependent queuing networks that incorporate
distribution of travel times (Chelst and Jarvis 1979),           a mean-value-analysis algorithm and unconstrained
and allowing the dispatch of multiple units (Chelst              optimization to solve problems in which the widths
and Barlach 1981). Researchers have suggested that               of circulation paths in buildings can vary.
these queuing models can be used as subroutines                     Analysts have developed micro-, macro-, and
in optimization heuristics (Berman and Larson 1982,              mesosimulation models for planning evacuations.
Benveniste 1985, and Berman et al. 1987). Carter et al.          Micro-simulations track the detailed movements of
(1972), Hall (1972), and Chelst (1981) developed other           individual entities (cars, trucks, or people) on the
analytic approaches.                                             road network. Pidd et al. (1996) and de Silva and
   Savas (1969) used simulation analysis to evalu-               Eglese (2000) describe their development of a spa-
ate proposed changes to the number and location of               tial decision-support system (SDSS) for contingency
ambulances in New York. Fitzsimmons (1973) com-                  planning in emergency evacuations using a micro-
bined queuing and simulation to estimate the prob-               simulation model linked to a geographical informa-
abilities of particular ambulances being busy. This              tion system (GIS). Mould (2001) used discrete-event
approach was combined with a pattern search routine              simulation to plan the emergency evacuation of an
Wright, Liberatore, and Nydick: Survey of Operations Research Models and Applications in Homeland Security
Interfaces 36(6), pp. 514–529, © 2006 INFORMS                                                                             521

offshore oil installation. He considered environmen-                   of considering the stochastic and time-varying nature
tal conditions, such as wind speed and wave height,                    of travel conditions in emergency situations, Miller-
while using a prespecified routine for evacuation and                   Hooks and Mahmassani (1998) developed and tested
assessed the use of helicopters alone or in conjunc-                   two algorithms for determining the shortest path
tion with fast rescue craft. He applied the model to a                 under such conditions. Several authors have modeled
fictitious incident using randomly generated weather                    the problem of transporting vital first-aid commodi-
data. Jha et al. (2004) developed a micro-simulation                   ties and emergency personnel to disaster-affected
model to evaluate five scenarios for evacuation plan-                   areas. Haghani and Oh (1996) used a deterministic
ning at Los Alamos National Laboratory. Helbing                        multicommodity, multimodal network flow model to
et al. (2005) developed simulation models of pedes-                    plan disaster relief. Barbarosoglu and Arda (2004)
trian flows and used the results of these models as                     extended this approach to include random arc capac-
well as experiments to recommend designs to increase                   ity, supply, and demand. They formulated the prob-
the efficiency and safety of facilities and egress routes.              lem as a two-stage stochastic program and used
Using behavioral information, Stern and Sinuany-                       data from the August 1999 earthquake in Marmara,
Stern (1989) used micro-simulation to plan evacuation                  Turkey.
under a radiological event.                                               Srinivasa and Wilhelm (1997) and Wilhelm and
   Macro-simulations do not track individual entities                  Srinivasa (1997) developed a model that prescribes
but use equations based on analogies with fluid                         an effective response to an oil spill, which requires
flows in networks (Sheffi et al. 1982). Southworth
                                                                       such decisions as which components to dispatch, how
and Chin (1987) used macro-simulation to study the
                                                                       many, and when. They formulated the problem as a
evacuation of a population threatened by flooding
                                                                       general integer program, using graph theory to gener-
from a failed dam based on empirical data from urban
                                                                       ate response systems (components and their locations)
and rural areas. A compromise approach is to use
                                                                       needed by the model. They applied their approach
meso-simulators that usually track the movement of
                                                                       to actual data representing the Galveston Bay area.
groups of entities.
                                                                       They applied a heuristic (Wilhelm and Srinivasa 1997)
Disaster Planning and Response                                         and an exact procedure based on strong cutting-plane
How individuals and organizations respond to dis-                      methods (Srinivasa and Wilhelm 1997).
asters is important in preparing for emergencies.                         A few researchers have modeled human behav-
Belardo et al. (1984a) discussed response problems                     ior in emergency situations. Reer (1994) developed
faced by four organizations: the American Red Cross,                   a probabilistic procedure to analyze human reliabil-
the US Coast Guard, the Regional Emergency Medi-                       ity in emergency situations using time windows and
cal Organization in Albany, New York, and the New                      organizational input data. Reer used the loss of main
York State Office of Disaster Preparedness. Averett                     feedwater at a pressurized water reactor plant as an
(2005) discussed four examples of responding to and                    example to investigate several organizational alter-
preparing for disasters using various modeling tools:                  natives. Doheny and Fraser (1996) developed a soft-
(1) discrete optimization and simulation models for                    ware tool that can be used to model human decision
locating and configuring vaccination centers and redi-                  making during emergency situations. Their model
recting the flow of patients, (2) a graphics tool for                   includes frames to represent a person’s characteris-
visualization and collaboration, (3) simulation for dis-               tics and perception of the environment, and scripts to
aster management training, and (4) game theory to                      define typical behaviors for particular situations. They
anticipate terrorist attacks and defend against them.                  used their model to simulate an offshore emergency
Kananen et al. (1990) extended standard input-output                   scenario.
models and used multiobjective linear programming
to evaluate the potential impact of emergencies or dis-
asters on the Finnish economy.                                         Threat Analysis
   Routing emergency vehicles is important in re-                      Threat analysis develops the capabilities to evaluate
sponding to emergencies. Recognizing the importance                    and disseminate extensive information about threats
Wright, Liberatore, and Nydick: Survey of Operations Research Models and Applications in Homeland Security
522                                                                                         Interfaces 36(6), pp. 514–529, © 2006 INFORMS

and to identify planned attacks. The US government                and Horowitz (2004) modeled counterterrorism intel-
obtains extensive information on threats daily, and               ligence using a two-player hierarchical holographic
threat analysis research attempts to detect and doc-              modeling game. Kaplan et al. (2005) introduced a
ument terrorists’ intentions. Raghu et al. (2005) dis-            terror-stock model that estimates the size of terrorist
cussed a collaborative decision-making framework                  groups and how that size changes when the terrorists
for homeland security and a connectionist modeling                themselves are attacked.
approach that fuses disparate information from sev-
eral sources.
   Popp et al. (2004) approached threat analysis from
                                                                  Discussion and Future Research
an information technology (IT) perspective. They                  Operations research has contributed to issues related
argued that improved IT can reduce the time needed                to homeland security in the United States even
for searching for data, harvesting data, preprocessing            before 2001, when homeland security was defined.
data, and turning the results into reports and briefs.            We adopted the research framework used by the
They discussed three core IT areas in depth: collabo-             US Department of Homeland Security’s science and
ration and decision tools, foreign-language tools, and            technology directorate to classify the literature. As a
pattern-analysis tools. These areas offer operations              result, we have not included some topics, such as the
researchers opportunities to work in conjunction with             military that in some cases could be considered home-
information technologists to reduce terrorist attacks             land security.
and their effects.                                                   We used a two-dimensional framework in exam-
   Wang et al. (2004) developed an algorithm that                 ining the previous OR work in homeland security:
looks for similarities in criminal identities. Using real         the areas specified by the US Department of Home-
data from a police department, they created a model               land Security and the four phases in the disaster life
that develops disagreement values for each pair of                cycle: planning, prevention, response, and recovery
criminal records. The intent is to use IT to determine            (Table 2). Planning is generally strategic and long
whether two criminal records represent the same per-              term in nature and relates to preparing for a disas-
son. Sheth et al. (2005) devised a process of semantic            ter. Planning examples include policy analysis, risk
association that links disparate information to estab-            analysis, systems design, and resource allocation. Pre-
lish relationships between terrorists. They incorpo-              vention efforts aim to identify and eliminate threats,
rated this methodology into a program that provides               for example, screening airline passengers or patrolling
a 360-degree look at each passenger boarding a flight              borders. Response activities occur immediately after
and develops a threat score for use in deciding about             a disaster and include stabilizing affected areas,
additional security screening.                                    immediate medical care, and evacuation. Finally,
   Pate-Cornell (2002) studied the fusion of intelli-             recovery focuses on returning the affected areas and
gence information from different sources and used                 populations to their pre-event status and includes
Bayesian analysis to rank threats and to prioritize               restoring critical infrastructures, assisting affected
safety measures. Dombroski and Carley (2002) used                 persons, and coordinating relief efforts.
Bayesian analysis and biased network theory to esti-                 Despite the attention paid to component support,
mate patterns of links between different cells of                 many critical issues remain to be addressed within
a terrorist organization to predict the structure of              this category. Green and Kolesar (2004) described
the terrorist network. Other researchers who devel-               how component support problems are evolving. They
oped Bayesian methods to aid in decision making                   suggested that analysts need to work on nonrou-
are Santos (1996), Santos and Young (1999), and                   tine emergencies and coordinating emergency service
Santos et al. (2003). Santos and Haimes (2004) used               providers, and preparing for and responding to ter-
input-output and decomposition analysis to provide a              roristic acts.
framework for describing how various terrorist activ-                A wealth of literature concerns the security of
ities are connected. They prioritize sectors based on             trucks transporting hazardous materials, largely such
the economic impact of terrorist activities. Haimes               issues as routing them to avoid exposing populations
Wright, Liberatore, and Nydick: Survey of Operations Research Models and Applications in Homeland Security
Interfaces 36(6), pp. 514–529, © 2006 INFORMS                                                                                                                        523

Category                                             Planning                                     Prevention                            Response                  Recovery

Countermeasures portfolios
  Biological                       Hupert et al. (2002)                              Sullivan and Perry (2004)              Buckeridge et al. (2005), Craft
                                                                                                                              et al. (2005), Kaplan et al.
                                                                                                                              (2002, 2003), Stuart and
                                                                                                                              Wilkening (2005), Wein et al.
  Chemical                         Jenkins (2000)
  Radiological and nuclear                                                           Butler et al. (2005), Dyer et al.
                                                                                       (1998), Munera et al. (1997)
  High explosives
Component support portfolios
  Border and transportation
    Border security                Wein and Baveja (2005)
    Airline security               Barnett et al. (2001), Candalino et al. (2004),   Barnett (2004), Gilliam (1979),
                                     Leone and Liu (2003), Virta et al. (2003)         Jacobson et al. (2000, 2001,
                                                                                       2003, 2005), Kobza and Jacobson
                                                                                       (1996, 1997)
    Port and rail                  Glickman and Rosenfield (1984), Harrald
                                      et al. (2004), Lewis et al. (2003)
    Truck                                                                            Batta and Chiu (1986, 1988),
                                                                                       Berman et al. (2000), Beroggi and
                                                                                       Wallace (1994, 2005), Erkut and
                                                                                       Ingolfsson (2000, 2005), Erkut
                                                                                       and Verter (1998), Giannikos
                                                                                       (1998), Gopalan et al. (1990), Jin
                                                                                       et al. (1996), Kara et al. (2003),
                                                                                       Karkazis and Boffey (1995),
                                                                                       Lindner-Dutton et al. (1991), List
                                                                                       and Turnquist (1998), Raj and
                                                                                       Pritchard (2000), van Steen
                                                                                       (1987), Zografos and
                                                                                       Androutsopoulos (2004)
  Critical infrastructure          Apostolakis and Lemon (2005), Brown et al.        Baskerville and Portougal (2003)       Zografos et al. (1998)
     protection                      (2004), Salmeron et al. (2004)
  Cyber security                   Krings and Azadmanesh (2005)                      Chowdhury et al. (1999), Muralidhar    Abouzakhar and Manson (2002),
                                                                                       et al. (1999)                          Chen et al. (2005), Shindo
                                                                                                                              et al. (2000)
  Emergency preparedness
  and response
    Early work                     Carter and Ignall (1970), Carter and Rolph                                               Carter et al. (1972), Ignall et al.
                                     (1974), Chaiken and Dormont (1978a, b),                                                  (1982), Swersey (1982)
                                     Chelst (1988, 1990), Green (1984),
                                     Green and Kolesar (1989), Kolesar
                                     et al. (1975), Ignall et al. (1975), Kolesar
                                     and Blum (1973), Kolesar and Walker
                                     (1974), Larson (1972), Rider (1976),
                                     Walker (1974)
                                                                                                                                                 Table continues next page

                       Table 2: Homeland security literature classified along two dimensions reveals opportunities for future research.
                       We show where each paper fits within the Department of Homeland Security’s research framework and its position
                       within the disaster life cycle. The two-dimensional framework in this table illustrates where the bulk of OR
                       models and applications in homeland security exist. This table also highlights important gaps for future research.
                       Focusing first on the rows in the table, we see that the topics that have received the most attention fall under
                       the component support portfolios. Emergency preparedness and response contains significant amounts of work,
                       with emphasis on emergency services location and resource allocation. Other highly important issues that have
                       seen significant attention are evacuation models and disaster planning and response.
Wright, Liberatore, and Nydick: Survey of Operations Research Models and Applications in Homeland Security
524                                                                                                                    Interfaces 36(6), pp. 514–529, © 2006 INFORMS

Category                                            Planning                                     Prevention                           Response              Recovery

      Location and resource      Akella et al. (2005), Ball and Lin (1993), Batta
        allocation                 and Mannur (1990), Batta et al. (1989),
                                   Belardo et al. (1984b), Benveniste (1985),
                                   Berman et al. (1987), Berman and
                                   Larson (1982), Bianchi and Church
                                   (1988), Brandeau and Larson (1986),
                                   Carter et al. (1972), Chelst (1981), Chelst
                                   and Barlach (1981), Chelst and Jarvis
                                   (1979), Church and ReVelle (1974),
                                   Current and O’Kelly (1992), Daskin
                                   (1983), Daskin and Stern (1981), Eaton
                                   et al. (1985), Fitzsimmons (1973),
                                   Fitzsimmons and Srikar (1982), Goldberg
                                   and Paz (1991), Hall (1972), Halpern
                                   (1977), Hogan and ReVelle (1986),
                                   Larson (1974, 1975, 2001), Larson and
                                   Rich (1987), Pirkul and Schilling (1988),
                                   Plane and Hendrick (1977), ReVelle and
                                   Hogan (1989), Saccomanno and Allen
                                   (1988), Savas (1969), Schilling et al.
                                   (1979), Swoveland et al. (1973), Tavakoli
                                   and Lightner (2004), Toregas et al. (1971),
                                   Walker (1974)
      Evacuation models          Bakuli and Smith (1991, 1996), de Silva and                                               Chalmet et al. (1982)
                                   Eglese (2000), Helbing et al. (2005), Jha
                                   et al. (2004), Mould (2001), Pidd et al.
                                   (1996), Sheffi et al. (1982), Smith (1991),
                                   Smith and Towsley (1981), Southworth
                                   and Chin (1987), Stern and Sinuany-Stern
                                   (1989), Talebi and Smith (1985)
      Disaster planning and      Barbarosoglu and Arda (2004), Doheny and                                                  Averett (2005), Belardo et al.
         response                  Fraser (1996), Haghani and Oh (1996),                                                     (1984a), Srinivasa and
                                   Kananen et al. (1990), Miller-Hooks and                                                   Wilhelm (1997), Wilhelm and
                                   Mahmassani (1998), Reer (1994)                                                            Srinivasa (1997)
  Threat analysis                Dombroski and Carley (2002), Haimes and            Sheth et al. (2005), Wang et al.       Santos (1996), Santos and
                                   Horowitz (2004), Kaplan et al. (2005),             (2004)                                 Young (1999), Santos et al.
                                   Pate-Cornell (2002), Popp et al. (2004),                                                  (2003)
                                   Raghu et al. (2005), Santos and Haimes

                      Table 2: Continued.

unnecessarily and analyzing risks. Researchers should                                  researchers and physical scientists, similar to that of
extend these models to incorporate homeland security                                   Craft et al. (2005). OR methods are well suited for
issues, for example, protecting trucks against terrorist                               problems pertaining to cyber security, critical infras-
hijacking.                                                                             tructure protection, threat analysis, and border secu-
   Much of the extensive research on airline security                                  rity; however, work in these areas so far is limited
has limited applicability because of changes in secu-                                  (Table 2).
rity systems and policies. Operations researchers have                                    We classified papers in the disaster life cycle based
many new opportunities to contribute in this area.                                     on their main focus (Table 2). The literature has gaps
   The countermeasures and component support port-                                     with respect to some phases in the disaster life cycle.
folios offer many other opportunities for contribution.                                Most OR research in homeland security concerns plan-
The literature on the countermeasures portfolio is in-                                 ning. Some concerns prevention, but we uncovered no
creasing, but many issues still need exploration. Some                                 papers on the recovery phase and very few on the
would benefit from collaboration between operations                                     response phase. There is a need for more research on
Wright, Liberatore, and Nydick: Survey of Operations Research Models and Applications in Homeland Security
Interfaces 36(6), pp. 514–529, © 2006 INFORMS                                                                                           525

decision making after the disaster. As the 2005 hur-                   Proceedings of the National Academy of Sciences Web
ricanes made clear, we need to respond effectively                     site. Despite such possible restrictions, operations re-
to large-scale disasters. Operations research modeling                 searchers have many opportunities to contribute to
incorporating the complex interconnections between                     homeland security.
relief agencies and government entities can clarify
these chaotic situations and help relief agencies to
coordinate their efforts. Operations researchers have                  References
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