If you can't control the car then I am inclined to think you have a controlling nature due to an underlying fear of actually having no-control over your life or life-path. It's like an overcompensation where you try to control as much as possible because otherwise being out of control feels as awful as when you were in that "out of control" car. The dream would be trying to get you to see these connections so you could find a way to nurture more trust in yourself and life without the need to over-exert influence.