According to the book "Competing Rails: The Milwaukee Road's Legacy in Wilmette and Evanston" (Shore Line Interurban Historical Society Dispatch Number 2, 2011) the westernmost track, at least in Evanston, was for freight service. The Milwaukee Road continued freight service over the line up to Wilmette until 1920 when the Northwestern Elevated (predecessor of the CRT/CTA) took over using the Buena Yard at Irving Park for interchange. Milwaukee Road passenger service over the C&E ended in 1917.
I highly recommend Competing Rails for anyone interested at all in the history of the Chicago & Evanston branch line of the Milwaukee Road. Tons of photos, track diagrams, and maps.
Tom