  In a transport network, the onboard occupancy is key for gaining insights
into travelers' habits and adjusting the offer. Traditionally, operators have
relied on field studies to evaluate ridership of a typical workday. However,
automated fare collection (AFC) and automatic passenger counting (APC) data,
which provide complete temporal coverage, are often available but
underexploited. It should be noted, however, that each data source comes with
its own biases: AFC data may not account for fraud, while not all vehicles are
equipped with APC systems.
  This paper introduces the unified occupancy method, a geostatistical model to
extrapolate occupancy to every course of a public transportation network by
combining AFC and APC data with partial coverage. Unified occupancy completes
missing APC information for courses on lines where other courses have APC
measures, as well as for courses on lines where no APC data is available at
all. The accuracy of this method is evaluated on real data from several public
transportation networks in France.
