Nouns ending in -tion are feminine.
The suffix forms abstract nouns of action or state.
Is circulation masculine or feminine?
lacirculation
The rule behind it
99.8% of -tion nouns are feminine
In context
La circulation est dense ici, surtout le matin.
The traffic is heavy here, especially in the morning.
Vous devez vous conformer aux règles de circulation.
You must obey the traffic rules.
Les conducteurs devraient connaître les règles de circulation.
Drivers should know traffic rules.