In Ballard v. State, 757 S.W.2d 389 (Tex.App.--Houston 1st Dist. 1988, pet. ref'd), the defendant was found unconscious, slumped over the driver's wheel. Ballard, 757 S.W.2d at 390. The vehicle was parked on the shoulder of the highway with the engine still running. The State offered no evidence indicating how long the vehicle had been parked on the shoulder. The defendant admitted to police that he had been driving the vehicle but the court of appeals held that his uncorroborated admission was not sufficient to prove that he had operated the vehicle. Id.