Do you know the meaning of primary?

ICBC/Western Insurance poster, Vancouver, BC

ICBC/Western Insurance poster (Detail), Vancouver, BC

I'm confused. (Not a new situation.)

How can you say "A primary driver"? There can only be one primary driver, everyone else is, by definition, secondary or tertiary.

And what does "Does anyone drive your car over 50% of the time?" really mean? 50% of the driver's driving time, or 50% of the time your car is driven by anyone?

Clarity in marketing communications is critical, but sometime it seems very hard for firms to actually achieve it.