a two-stage solution strategy is described, where the emergency vehi- cle assignment constrains subsequent decisions on lane reversal and intersection use. A brief description is provided of the Lagrangian relaxation and tabu search method that solves the evacuation net- work optimization problem. The model and solution procedure are illustrated in an evacuation case study for a nuclear power plant in Monticello, Minnesota. MODEL FORMULATION The core idea of integrating the treatment of lane reversals and crossing elimination in evacuation network design is illustrated by the examples in Figure 1, which show how controlling lane entries and turning movements at intersections can create uninterrupted flow conditions for specific evacuation paths. The intersections must be expanded into subnetworks, as shown in Figure 2, to model an evacuation network design that uses lane-reversal and crossing- elimination strategies. Figure 2 also illustrates how intermediate nodes are introduced into roadway sections to serve as origins of evacuation trips. The parameters, sets, and variables used in the model are listed below. Parameters and sets n ικ,ϑρ = total number of lanes of two adjacent link pairs ι→ς →κ and ϑ→τ→ρ in a roadway-section subnetwork c ις (n ικ ) = capacity of roadway-section link ι→ς, as a function of lanes allocated to the traffic direction ι→κ u ηι = dummy capacity of link η→ι, where η→ι is an inter- section link t 0 ις = free-flow travel time on link ι→ς, where ι→ς is a roadway-section link b ς = net flow rate at node ς S ι = set of the starting nodes of links pointing to node ι R ρ = set of the ending nodes of link emanating from node ρ Variables n ικ = number of lanes on link pair ι→ς→κ, where ι→ς→κ is a pair of consecutive roadway-section links n l ικ = number of reserved lanes for emergency vehicle us on roadway link pair ι→ς→κ x ις = evacuation flow rate on link ι→ς t ις = travel time on link ι→ς, where t ις is a function of x ις and n ις y ηι = connectivity indicator of link η→ι, where η→ι is an intersection link y l ηι = connectivity indicator of link η→ι used by emergency vehicles, where η→ι is an intersection link Integrated Evacuation Network Optimization and Emergency Vehicle Assignment Chi Xie and Mark A. Turnquist 79 Three treatments are combined in the design of evacuation network operating plans: reversing lanes, eliminating intersection crossings, and reserving lanes for use by emergency vehicles. An optimization approach is taken and casts the problem as a form of discrete network design, with constraints imposed by emergency vehicle lane assignment. What have previously been separate strands of work examining ways of configuring road networks for effective evacuation performance are integrated. A case study for a network around a nuclear power plant illustrates the usefulness of this integrated approach. Evacuation is an important emergency response strategy to protect human populations from potentially catastrophic events. During the past three decades, considerable research has been conducted on developing evacuation plans. Recently, interest in lane-reversal schemes to increase available evacuation capacity has grown (1–4). Many evacuation routes are at least partially on signal-controlled arterials, and intersections usually are the capacity-limiting parts of the network. At least two studies have focused on or included inter- section crossing elimination as a strategy to reduce overall delay in defining an evacuation network (5, 6). The basic rationale for elimi- nating crossings during an evacuation is to convert an intersection from interrupted to uninterrupted traffic flow by prohibiting some turning movements, blocking lane entries, and limiting flow direc- tions. The first objective of the present study is to combine lane rever- sal with intersection crossing elimination into an integrated approach to evacuation network design. Evacuation performance (measured by network clearance time or total evacuation time, for example) is a vital characteristic of an evac- uation network design, but it is also important to consider access to the evacuation area by emergency vehicles and equipment (7, 8). Furthermore, if buses are an integral part of the evacuation strategy, then they need to be able to return to the area to pick up more peo- ple. The need for inbound access to the area being evacuated may conflict with the desire to maximize outbound capacity, particularly when lane reversal strategies are used. The second objective of the work presented in this paper is to incorporate emergency vehicle route assignment into the evacuation network design process. In the following section, a model formulation of evacuation net- work design is presented as an explicit optimization problem. Next, C. Xie, Center for Transportation Research, Department of Civil, Architectural, and Environmental Engineering, University of Texas, Austin, TX 78759. M. A. Turnquist, School of Civil and Environmental Engineering, Cornell University, Ithaca, NY 14853. Corresponding author: M. A. Turnquist, mat14@cornell.edu. Transportation Research Record: Journal of the Transportation Research Board, No. 2091, Transportation Research Board of the National Academies, Washington, D.C., 2009, pp. 79–90. DOI: 10.3141/2091-09