From:
http://www.answers.com/topic/conrail-sh ... operations
Conrail Shared Assets Operations (AAR reporting mark CSAO) is an American railroad company. It operates three networks - the North Jersey, South Jersey/Philadelphia, and Detroit Shared Assets Areas, where it serves as a local carrier and switching company for CSX Transportation and the Norfolk Southern Railway. When most of the former Conrail's track was split between these two railroads, the three shared assets areas were kept separate to avoid giving one railroad an advantage in those areas.
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What is it? Shortline? Third party switching?