How these routes evolved into routes operated by IPTC, is covered at the Route History page.
Beech Grove Traction Co. - suburban trolley line began operation in 1911, connecting with Shelby streetcar line and operating into Beech Grove. In 1929, acquired South Side Motor Coach Co., which had begun a competing bus operation in 1925. Bus operation sold in 1936, and trolley line discontinued in 1937. Bus operation reorganized in 1937 as Beech Grove Transit Co., sold to Indianapolis Railways/People's Motor Coach Co. in 1941.
L. J. Smith Transportation Co. - incorporated 1937 as reorganization of Logan J. Smith's jitney and charter bus operations. Sold to Indianapolis Railways/People's Motor Coach Co. in 1941, operated bus routes serving Sunshine Gardens and operating via Kentucky Ave. Both routes were discontinued shortly after World War II.
Suburban Bus Co. - Indianapolis Street Railway Co. subsidiary formed in 1931 to operate local bus service, replacing discontinued Terre Haute Indianapolis & Eastern Traction Co. interurban trains, and operating via Washington St. and Rockville Rd. west of Indianapolis. Subsdiary absorbed into main company in 1941, and route sold to Danville Bus Lines in 1950.
Post Way Transit, Inc. - acquired by Indianapolis Railways in 1944, one route operated mainly via east 10th St., discontinued in 1952 as largely redundant to existing routes.
Also, between 1938 and at least the 1960's, there existed a company Indianapolis & Martinsville Transit Lines, whose namesake cities were until 1930 connected by an interurban railway line.
Fort Harrison Bus Line - original bus service replaced discontinued Indiana Railroad interurban trains in 1941. Indiana Railroad continued to operate buses until 1950, when the bus operations were sold to Indianapolis & Southeastern Trailways. Now an IndyGo route.
Central Swallow Coach Lines - began operating buses as early as 1935, east of Indianapolis to Dunreith and New Castle, replacing the THI&E railway line which had been abandoned in 1932. Now part of the IndyGo Washington route.
Suburban Lines, Inc. - began operating buses south of Indianapolis to Greenwood and Franklin in 1941, replacing the former Interstate Public Service Co. railway line which had operated to Seymour and Louisville. Now part of the IndyGo Madison route. Added new route north to Zionsville by 1949, now part of the IndyGo Michigan route.
Indianapolis Transit, Inc. - began operating after World War II west to Plainfield, providing local bus service along the abandoned former THI&E railway route towards Terre Haute. In 1950, acquired two Indianapolis Railways extension bus routes connecting with the west Washington St. trolleybus route. By 1968, Indianapolis Transit, Inc. acquired the Danville Bus Line, which had begun operating buses between Indianapolis and Danville in 1936, replacing the THI&E railway line which had been abandoned in 1930. Now part of the IndyGo Washington route.