Industries in the Support Activities for Transportation subsector provide services which support transportation. These services may be provided to transportation carrier establishments or to the general public. This subsector includes a wide array of establishments, including air traffic control services, marine cargo handling, and motor vehicle towing.

The Support Activities for Transportation subsector includes services to transportation but is separated by type of mode serviced. The Support Activities for Rail Transportation industry includes services to the rail industry (e.g., railroad switching and terminal establishments).

Ship repair and maintenance not done in a shipyard are included in Other Support Activities for Water Transportation. An example would be floating drydock services in a harbor.

Excluded from this subsector are establishments primarily engaged in providing factory conversion and overhaul of transportation equipment, which are classified in Subsector 336, Transportation Equipment Manufacturing. Also, establishments primarily engaged in providing rental and leasing of transportation equipment without operator are classified in Subsector 532, Rental and Leasing Services.