Nice! I used to make the run up I-90-94 from my home location to the Twin Cities every 2-3 months (in the 80s, 3M was my biggest customer). Anyway, the drive took me through Madison. I know the rest area that you're talking about. North of the city around mile marker 113. I've heard WLW around there a few times, and at all times of year. I'm not sure if it's skywave or groundwave, or both. Or maybe just the Blaw-Knox tower at work.
BTW, as you may already know, When you get just north of that rest stop and cross the Wisconsin River, ground conductivity really starts to tank.