I'm confused by this... If the air molecules are staying roughly still, but the density of the air surrounding the vehicle rises by a factor of n, isn't the veh

I'm confused by this... If the air molecules are staying roughly still, but the density of the air surrounding the vehicle rises by a factor of n, isn't the vehicle colliding with n times as many particles as it would have otherwise? How is this more efficient? Is the velocity in the drag equation relative to the vehicle, or to a stationary frame of reference? Edit: Or is the point that the velocity of the air particles within the density peak is at its maximal forward-traveling rate before they start to loop back around and form their ellipse?