Final Shot With Red Sunset - Matte Painting?

does anyone know anything about the final shot with that reddish sunset? Was that authentic? if so, it was some spectacular timing by walter hill. my first instinct was that it's a matte painting like the ones hollywood made common use of in those days, except that the span was so huge and the cars on the street seemed to be real, and moving, so in my thinking that would make the scale of t he painting pretty much impossible.

just wondering if anyone knows anything about that shot.

like i said, it's pretty impressive Hill could time that set-up just right to catch that red sky, unless it was purely incidental and he got lucky by chance.

thanks in advance.

peace.