hobbesvsboyle
Huh, I checked again, and now it's no longer there. Pretty sure I used the Street Centerlines or maybe the Transportation Planning datasets on the Open Data portal https://data-cityofmadison.opendata.arcgis.com/datasets/street-centerlines-and-pavement-data/explore?location=43.117747%2C-89.271213%2C15.85
So I'm guessing this was a planned facility that fell through. I'll resolve the comment for now.