I was driving on a beautiful summer day. at 12;30 pm on a highway. i observed what i originally thought was a plastic bag appear over the tree line in the top right corner of my car windshield. i could not tell the size of the object but it caught my eye. i was a circle and i thought it was a bag at first. however, it moved in a perfectly straight line and at a steady rate of speed. about 1/2 way across my windshield the circular object turned quickly and became flat like a frisbee. that the best way i can describe it. the object continued at the same rate of speed and at the same altitude for another 15 seconds. i watched it go from north to south (right to left across my field of visiion) until i lost sight of it in background cloud cover. i did not see any lights or color other than white. after i lost sight of the object i saw a helicopter fly in the opposite direction at what appeared to be the same attitude. i wish i had another passenger with me to confirm what i witnessed.