ABSTRACT The coordination of emergency services in road accidents is essential to ensure a quick intervention in critical situa- tions. The number and kind of resources assigned must be determined dynamically, as not all the accident variables are known when an alert is received. Moreover, vehicles and intervention units have to be assigned after the acci- dent takes place. Thus, the decision making process has to be done within the intervention time window and response time becomes critical. This paper describes the major char- acteristics of a cluster first-route second optimization algo- rithm suggested to tackle the emergency services coordina- tion problem in order to reduce their response time in critical situations. This algorithm combines heuristic meth- ods and Constraint Satisfaction Problem techniques in a two-stage procedure: a first phase where the real geo- graphic data is rearranged to ensure the time constraints fulfillment and a second one, which consists on available resources' allocation and optimal routes assignment. INTRODUCTION The complexity of tasks carried out in a road accident re- quires the intervention of multidisciplinary rescue services, i.e. Police Service, Medical Service and Fire Service, and their coordination is a key issue to ensure an effective in- tervention. Therefore, correct management of these three heterogeneous fleets is necessary to distribute units and re- spond to dynamically changing real needs. Such a coordination is highly complex, since not all the information relative to accident variables is known from the very beginning and the available information usu- ally contains uncertainty. Furthermore, although some col- laboration protocols are defined, they only regulate ser- vices interaction at the accident scene, but they not include general norms about resources' assignation (Samur, 2006). Centralized communication, coordination and decision tasks would improve rescue services response, reducing rescue time and optimizing the available resources. Attending an accident basically consists of deciding which resources are assigned and from which depot they have to be selected, taking into account all the accessible information and that the objective is to reduce the route travel time. The allocation task is performed using the fleet variables, including available units type and state, but not considering vehicles crew assignment. Time restrictions are naturally imposed due to the re- action time is primordial to save possible accident victims. Thus, the routes planning expended time becomes critical, since they have to be assigned within intervention's time window. Road network configuration and depots (fleet bases) distribution are also important issues that determine the emergency fleets' capability to respond a concrete situation. The number and kind of mobilized resources in a par- ticular situation depends on the accident variables, such as the number of involved vehicles, traffic ratio on the road and time when the accident takes place or whether there are injured victims or not. Furthermore, resources are dy- namically assigned since information flow is continuous from the moment the accident occurs until services finish their action. A simulation platform (Ramos et al., 2006) has been designed as a distributed application based on CORBA (OMG, 2004) to simplify the coordination and communica- tions between modules. A Geographical Information Sys- tem (GIS) module manages all the static and dynamic geo- graphical data in the system, such as depots location and the road network configuration (Ramos et al., 2005), used to compute realistic travel time and costs. However, the huge amount of data provided by these databases would make the problem, which falls into the Vehicle Routing Problem (VRP) category (Bektas, 2006), intractable in a real-world case due to the computation time. Due to the NP-Hardness of the problem, no exact algo- rithm can be assured to find optimal solutions within rea- sonable computing time, so near all the solution techniques for this problem are heuristics (Laporte et al., 2000) and metaheuristics (Glover and Kochenberger, 2003). These methods has demonstrated being effective in the search of good solutions within acceptable calculation time, though A TWO-STAGE APPROACH FOR THE EMERGENCY SERVICES COORDINATION PROBLEM IN A ROAD ACCIDENT D. Guimarans, J.J. Ramos Telecommunication and System Engineering Department – LogiSim, School of Engineering, ETSE, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain. {Daniel.Guimarans, JuanJose.Ramos}@uab.cat