Surprised by disc hovering above the highway in front of me.

I have withheld reporting this event for 44 years.
While driving south on South Lake Shore Drive leaving downtown Chicago, I saw an air born object fly from above Lake Michigan and stop, then hover directly over Lake Shore Drive in front of me at a height of approximately 2000 to 5000 feet.
It appeared to be quite large and so close that I could clearly see it was a disc shaped object with a continuous single row of what appeared to be lighted square windows completely surrounding its perimeter. Its only other characteristic was that it appeared to be slowly revolving horizontally. An awkward estimation of its size would be 500 feet across. It did not emit any sound at any time during the event.
After about 30 seconds it slowly moved with increasing speed back over the Lake, stopped and hovered there for a few seconds, then darted very very quickly further over the Lake and out of sight over the horizon. Although I slowed slightly as I viewed this event in amazement, the traffic on the highway was brisk and prevented me from stopping.
The witness who was riding beside me in the car also saw this event, but thought better of reporting it as she was and still is of he character of not drawing any sort of attention to herself, and after 42 years of marriage continues to be in denial regarding this event stating she does not remember it as she fears that people will laugh at her. Since she would not back up our mutual sighting, I never reported it until now.
This event remains as one of the few vivid memories in my life and I will never forget it.
Witness indicates that date of incident is approximate.  PD