I've got a similar looking jacket, does your's have a fleece like exterior? Mine does, and it seems to soak through pretty easy in the rain.
I'm also an occasional Beltway traveler and there is no way I'd
ever want to want to break down on it.
The exterior feels more like a thin felt than fleece. The inside is a light fleece.
I have not worn it in the rain. It sure is bright!
The Beltway and I-270 -- gives me the heebie-jeebies to think about being stranded on either. You'd be a sitting duck.
On that note, I just got a reflective safety triangle from Red Flare. It augments a strobe light and LED road flare:
http://www.llbean.com/llb/shop/65534?feat=9519-GN2