  This paper deals with a multi-period extension of the p-center problem, in
which arc traversal times vary over time, and facilities are mobile units that
can be relocated multiple times during the planning horizon. The problem arises
in several applications, such as emergency services, in which vehicles can be
relocated in anticipation of traffic congestion. First, we analyze the problem
structure and its relationship with its single-period counterpart, including a
special case. Then, the insight gained with this analysis is used to devise a
decomposition heuristic. Computational results on instances based on the Paris
(France) road graph indicate that the algorithm is capable of determining
good-quality solutions in a reasonable execution time.
