And to tie up a loose end, there's a WI 318 marker at its intersection with US 18/Summit Avenue. So US 18's not-in-use CRTT_Wau label can be replaced with WI318 (that waypoint could also be recentered).
I saw the 318 marker last month, on what turned out to be a futile effort to finish off US 18 in Wisconsin. With the weird US 18 signage in the Waukesha area, I'm not shocked that clinch didn't last long.