This happened more than 10 years ago so the details are sketchy. I'm also not sure if it was in 1990 or 1991.

It was very early evening, still light, and as I stopped at a stop sign on a fairly busy suburban throroughfare, I noticed what I thought was stadium lights on some spare ground that was being made into a park, about 100 feet to my right. Instead of stadium lights, there was a large metal, flattened ovoid-disc, machine(?) hovering just above the trees. No noise. I'm not good at judging size but I'd guess it was around 40-60 feet in diameter. It had a ring of very bright lights circling its lower rim. As I continued very slowly along beside it, it moved, also slowly and very smoothly, in the same direction. It moved with facility and seemed not to be labouring under its own weight.
This continued for about a quarter mile. It was slowly gaining altitude but continued on the same path. The road I was on began to veer away from our mutual direction but I watched it until it disappeared from view, as a plane would.
What I find stunning about this is that there were many cars on the road. The other travellers must have seen it - it was unmissable - but none of us did what one would expect folk to do under such circumstances, jump out of our cars and point and gawk.
I never heard anything about it in local media. I can say with conviction that it was not a helicopter, an aircraft or a blimp. Dunno!
Date is approximate.  PD