metalic, self propelled ball goes don the road

approximately volley ball sized, metalic ball travelling in oncoming traffic lane about 12 to 15 feet off of the ground. speed seemed to be no more than 60-75 mph. saw ball going around s curve and proceded past my driver side window. front seat passengers had clear view. rear passengers dozing. ball had no visable means of locomotion or exhaust. it had a mirror polish and joints which showed black streaks behind them. ball passed within 20 or so feet from my eyes.
One of two unrelated cases submitted by same witness.  Witness has considerable technical training and experience.  The witness indicates only the year in which the incident reportedly occurred, not a precise date.  We will attempt to obtain an exact date.  We have assigned a tentative date in 1994 until we receive a more accurate date.  PD