Mergers have improved this continuity. But a limit has been reached in the
network size of most rail operators. Attempts have been made to synchronize the
interactions between those operators, with the setting of intermodal unit trains for
long distance trade. Often bilateral, trilateral or even quadrilateral arrangements
are made between rail carriers and shipping companies to improve the intermodal
interface at major gateways, or at points of interlining between significant networks.
Chicago is the largest interlining center in North America, handling around
10 million TEU per year. Chicago is located at the junction of the Eastern (NS and
CSX), Western (UP, BNSF and KCS) and Canadian rail systems (CN and CP).
Other leading interlining locations include Kansas City, St. Louis and Memphis.