About Michigan's Belt Lines and Industrial Tracks
The term "belt" line suggests that the line circles a town or industrial. Few "belt" lines completely circled a city (a noted exception was the Toledo Terminal Railroad which circled the City of Toledo with mostly a double track main line).
Some belt lines were referred to as a "loop line". Others were called belt lines but they didn't actually "belt" anything. An example of this was the Jackson Belt Line, which was a two mile branch off the Michigan Central main line which served a number of industries on the east side of Jackson and Blackman Township.
Some belt lines had their own locomotives, but many used locomotives from owner roads, such as the Union Belt of Detroit which mostly used locomotives from the Wabash, PM and PRR.
Most belt lines and industrial tracks were operated under "Yard Limits" rules which required all trains to go slow and be able to stop within one half of the visual distance ahead. Many of these routes were under the supervision of a yardmaster or a series of yardmasters. Other belt lines had formal dispatchers, such as the Detroit Terminal and Toledo Terminal.