The Chicago division of the Grand Trunk Western (represented by the green lines on the map) consists of three subdivisions, the Flint, the South Bend, and the Kalamazoo subdivisions.

The Detroit division (represented by the red lines on the map) consists of 18 subdivisions. They are the Holly, Mount Clements, Saginaw, Midland, Grand Rapids, Coopersville, Greenville, Shore Line, River, Dearborn, Flat Rock, Paines, Harger, Napoleon, Romeo, Jackson, Cass City, and Springfield.

The Midland subdivision runs from Bay City, MI to Midland, MI which is about 18 miles. The maximum speed throughout the subdivision is 40 mph.

The Holly subdivision runs from Durand, MI to Detroit, MI which is about 67 miles. The maximum speed throughout the subdivision is 60 mph for Intermodal Trailer (or Container) On Flat Car and 55 mph for freight trains.

The Saginaw subdivision runs from Durand, MI to Bay City, MI which is about 55 miles. The maximum speed throughout the subdivision is 49 mph.

The Paines subdivision runs from Saginaw, MI to Paines, MI which is about 7 miles. The maximum speed throughout the subdivision is 10 mph.

The Grand Rapids subdivision runs from Durand, MI to Muskegon, MI which is about 124 miles. The maximum speed throughout the subdivision is 49 mph.

The Romeo subdivision runs from Owosso, MI to Carson City, MI which is about 39 miles. The maximum speed throughout the subdivision is 40 mph.

The Coopersville subdivision runs from Penn Jct, MI to Coopersville, MI which is about 8 miles. The maximum speed throughout the subdivision is 35 mph.

The River subdivision runs from Flat Rock, MI to Short Cut, MI which is about 17 miles. The maximum speed throughout the subdivision is 20 mph.

The Dearborn subdivision runs from Fordson, MI to Flat Rock, MI which is about 14 miles. The maximum speed throughout the subdivision is 40 mph.

The Flat Rock subdivision runs from Flat Rock, MI to Springfield, OH which is about 182 miles. The maximum speed throughout the subdivision is 55 mph.

The Napoleon subdivision runs from Malinta, OH to Napoleon, OH which is about 7 miles. The maximum speed throughout the subdivision is 20 mph.

The Springfield subdivision runs from Springfield, OH to Jackson, OH which is about 106 miles. The maximum speed throughout the subdivision is 40 mph.

The Flint subdivision runs from Port Huron, MI to Battle Creek, MI which is about 155 miles. The maximum speed throughout the subdivision is 65 mph for passenger, 60 mph for TOFC/COFC and 55mph for freight trains.

The South Bend subdivision runs from Battle Creek, MI to Chicago, IL which is about 178 miles. The maximum speed throughout the subdivision is 65 mph for passenger, 60 mph for TOFC/COFC, and 55 mph for freight trains.

The Jackson subdivision runs from Pontiac, MI to Wixom, MI which is about 15 miles. The maximum speed throughout the subdivision is 30 mph.

The Mount Clemens subdivision runs from Detroit, MI to Port Huron, MI which is about 55 miles. The maximum speed throughout the subdivision is 40 mph.

The Shore Line subdivision runs from Detroit, MI to Toledo, OH which is about 50 miles. The maximum speed throughout the subdivision is 40 mph.

The Cass City subdivision runs from Pontiac, MI to Imlay City, MI which is about 34 miles. The maximum speed throughout the subdivision is 40 mph.

The Romeo subdivision runs from Pontiac, MI to Richmond, MI which is about 38 miles. The maximum speed throughout the subdivision is 40 mph.

The Kalamazoo subdivision runs from Pavilion, MI to Kalamazoo, MI which is about 9 miles. The maximum speed throughout the subdivision is 20 mph.