It was the Motor Carrier Act of 1935 that prohibited railroads from owning motor carriers. Such operations that were in existence before the passage of that act were grandfathered.
The Santa Fe Trail Transportation Company was perhaps the dominant freight and passenger motor carrier in many parts of the western Midwest/Southwest region. The Santa Fe Trail Transportation Company's bus operation, known as Santa Fe Trailways, was one of the core companies that first former the National Trailways Bus System, and then many of the largest, dominated by Santa Fe Trailways, merged to form Transcontinental Bus Systerm, Inc., which continued to use the name of its large Texas (non-railroad-owned) component, Continental Trailways.
There were a number of such major motor carriers, both freight and passenger, organized before 1935 by major railroads, which continued in operation for many decades; their successors may continue to be in operation.
Wes Leatherock snipped-for-privacy@aol.com snipped-for-privacy@yahoo.com