Bright flash of light seen traveling southbnd on I-355 in Illinois during sunny day.I was driving south bound on I-355 just north of 159th st around 3:30 this afternoon. Today was around 45 degrees and sunny with very little cloud cover. I saw something that was very bright just east of me, which would be in the upper left portion of my windshield. At first I thought it was a plane with a sun reflection until I noticed a small black/dark object in the front section of the large light. I then thought either military jet or shooting star, but the light kept getting brighter and brighter then started to move in the southern direction. As it was moving south the light became dimmer and dimmer until all that was seen was a small black object. Almost as if something had a thruster attached to it? About 5 seconds after the dark object had dissapeared, I saw an object for a brief second much further south than where this object was first seen. I have to say I've seen plenty of aircraft before and shooting stars, but I've never witnessed anything like this before. Slow moving at first then extremely fast! Any kind of feedback would be great.