There are three Driver rarities in the game, Common, Rare and Epic. 

There will be a version of each driver for each rarity and these assets unlock at different Series. 

Equipping two identical Drivers with different rarities to the player’s team is not permitted. 

The assets of identical Drivers with different rarities are not added together.

Drivers can be sorted based on the following criteria:
Unlock order
Level
Rarity