Stochastic Emergency Response Units (ERUs) Allocation Considering Secondary Incident Occurrences

Abstract

Location of depots and routing of emergency response units are assumed to be interdependent in the incident management system. System costs will be excessive if delay regarding routing decisions is ignored when locating response units. This paper presents an integrated method to solve location and routing problem of emergency response units on freeways. The principle is to begin with a location phase for managing initial incidents and to progress through a routing phase for managing the stochastic occurrence of next incidents. Previous models used the frequency of independent incidents and ignored scenarios in which two incidents occurred within proximal regions and intervals. The proposed analytical model relaxes the structural assumptions of Poisson process (independent increments) and incorporates evolution of primary and secondary incident probabilities over time. The proposed mathematical model overcomes several limiting assumptions of the previous models, such as no waiting-time and returning rule to original depot. Our stochastic programming method hedges well against a wide range of scenarios in which probabilities of a sequence of incidents are assigned. The initial non-linear stochastic model is linearized. As a long-term strategy, the model incorporates flexibility in choosing the locations. The temporal locations flexible to a future policy-change are compared with current practice that locates all units in one permanent depot.