  In this paper we present a simulator allowing to perform policy experiments
relative to the air traffic management. Different SESAR solutions can be
implemented in the model to see the reaction of the different stakeholders as
well as other relevant metrics (delays, safety, etc). The model describes both
the strategic phase associated to the planning of the flight trajectories and
the tactical modifications occurring in the en-route phase. An implementation
of the model is available as open-source and freely accessible by any user.
  More specifically, different procedures related to business trajectories and
free-routing are tested and we illustrate the capabilities of the model on
airspace implementing these concepts. After performing numerical simulations
with the model, we show that in a free-routing scenario the controllers perform
less operations although they are dispersed over a larger portion of the
airspace. This can potentially increase the complexity of conflict detection
and resolution for controllers.
  In order to investigate this specific aspect, we consider some metrics used
to measure traffic complexity. We first show that in non-free-routing
situations our simulator deals with complexity in a way similar to what humans
would do. This allows us to be confident that the results of our numerical
simulations relative to the free-routing can reasonably forecast how human
controllers would behave in this new situation. Specifically, our numerical
simulations show that most of the complexity metrics decrease with
free-routing, while the few metrics which increase are all linked to the flight
level changes. This is a non-trivial result since intuitively the complexity
should increase with free-routing because of problematic geometries and more
dispersed conflicts over the airspace.
