Orange - Gary Railways and predecessors, along with Gary Railways successor Shore Line Motor Coach, later Chicago & Calumet District Transit Co.
Brown - Twin City Bus Lines, subsequently acquired by Shore Line Motor Coach, later Chicago & Calumet District Transit Co.
Blue - John E. Maloy, subsequently acquired by Shore Line Motor Coach, later Chicago & Calumet District Transit Co.
Yellow - Shelby Peterson, subsequently acquired by Shore Line Motor Coach, later Chicago & Calumet District Transit Co.
Purple - Farina's Bus Line & Transit Co., subsequently acquired by Shore Line Motor Coach, later Chicago & Calumet District Transit Co.
Green - Midwest Motor Coach Co., later Chicago & Calumet District Transit Co.
Several streets had routes from multiple predecessor bus companies. Most notably, several companies operated from downtown Hammond to downtown East Chicago, via State, Calumet, 150th St., Forsythe (now Indianapolis Blvd.), Chicago, Euclid, 141st St., Main, Guthrie.
Dashed lines indicate routes primarily serving various industries in the area.