What does ‘direction of departures’ mean?

Why does the Bison Futé service ( bison-fute.gouv.fr) use the expression ‘in the direction of the departures’ or ‘of the returns’ when warning of traffic congestion? What does it mean? P.J.

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This expression has been criticised as too Paris-orientated, but basically ‘departures’ refers to traffic heading from north to south (towards the Mediterranean) or west to east (towards mountain resorts in the Alps); returns is the opposite.