  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.
