Because the original poster replied in #3 that it wasn't that.
I asked someone at WADOT about the very same thing and was told they were to create an irregular surface in one or two of the lanes (notice the street view from down thread they are only in the right most/truck lane) to prevent perfect ice sheets from forming.
Seems awful coincidental that they'd be exactly at the joints between the concrete, as they are in that Street View, if they were added just to make an irregular surface as you say.
Maybe it's both things: they're holes from dowel bar retrofits as their look and placement sure seems to indicate, but they're only visible in one lane because the lane was purposely re- (de-?) surfaced. Or alternatively only the slow lane needed the retrofit at the time it was done just because it carried more of the heavy loads.
