Right now if you play a good driver in a BTB match you will get almost nothing score wise that is unless you are running power seeds solo with a razor back.
Bellow are some metal ideas and score bonuses for all.
Vehicle specific metals
Wheelman (five assists while driving in a life.)
Combat driver (10)
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Battle buss (25)
Razorking: 3 assists within 2 seconds while driving a razorback.
Power up: load a razorback with 5 power seeds. (2 on the back, and 3 being held.)
score change
Assist streaks, these give a bonus 100 score every 5 assists. these are not tied to single life.
battle buddy (5 assists)
wing man (10 assists)
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Fire support (25 assists)
Other metals
Overwatch: gets 5 long range assists
Suppressing fire: get 5 assists while using an HMG or mounted gun.
Airsuport: get 5 assists from the air.