The contact's daughter owns a 2019 Hyundai Tucson. The contact stated that his daughter had parked the vehicle and left it unattended while in the on position. After approximately 10-15 minutes, the daughter attempted to shut off the vehicle by turning the ignition key from the front passenger side, but after powering off the vehicle rolled backwards down the driveway, also dragging the daughter. While rolling backwards, the front passenger door hit the concrete mail box, and the vehicle continued to roll across the street before stopping in the neighbor's yard. During the incident, the daughter attempted to activate the emergency brake, but was unsuccessful. As a result, the daughter sustained several bruises to the right leg/knee and the back area, which did not require medical treatment. The passenger side door and the concrete mail box were damaged. The police were called to the scene, but no report was filed. The cause of the failure was not determined. The manufacturer and local dealer were not yet notified of the incident. The failure mileage was unknown.