behind the wheel
1. Driving a vehicle (and thus literally sitting behind the steering wheel). Don't worry, Katie's behind the wheel, and she hasn't been drinking tonight. I'm so excited to finally be behind the wheel of my own car!
2. In charge. With Jim behind the wheel, I'm not sure this team will have the leadership it needs.
at/behind the ˈwheel (of something)
driving a car: Who was at the wheel when the car crashed? Wheel in this phrase refers to the steering wheel of a car.