Very bright white oval shape gliding swiftly against the clear blue sky.

I was driving to work and saw an odd bright white craft coming from the west.  I thought it looked odd because it was so bright white and shiny like glass.  My mind started telling myself it was an airplane though it did not look like one at all.  It glided through the air so quickly and smooth.  The sky was very clear.  As I looked at it at the stoplight I saw a girl in her car next to me looking at it with an inquisitive face.  I tried to follow it but it completely disappeared.  I believe it was an oval shape and the brightest white you can imagine.