import flash.events.KeyboardEvent;
stage.addEventListener(KeyboardEvent.KEY_DOWN, motion);
stage.addEventListener(KeyboardEvent.KEY_DOWN, motion2);
    function motion(event:KeyboardEvent):void
    {
        if (event.keyCode == Keyboard.LEFT)
        {
            car.x-=10;
        }

        if (car.x<=50)
        {
            stage.addEventListener(KeyboardEvent.KEY_DOWN, motion2);
        }
    }

    function motion2(event:KeyboardEvent):void
    {
        if (car.x<=50)
        {
            car.scaleX*=-1;
            car.x+=15;
            car.y+=50;
            stage.removeEventListener(KeyboardEvent.KEY_DOWN, motion);
            stage.addEventListener(KeyboardEvent.KEY_DOWN, motion3);
        }
    }
    function motion3(event:KeyboardEvent):void
    {
        if (event.keyCode == Keyboard.RIGHT)
        {
            car.x+=10;
        }

        if (car.x>=500)
        {
            car.scaleX*=-1;
            car.x-=15;
            car.y-=50;

            stage.removeEventListener(KeyboardEvent.KEY_DOWN, motion2);
            stage.addEventListener(KeyboardEvent.KEY_DOWN, motion);
            stage.removeEventListener(KeyboardEvent.KEY_DOWN, motion3);
        }
    }