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The PennsylvaniaRailroad, once America's largest railroad by revenue and traffic volume and at one time the largest public corporation in the world, was headquartered in the city, as was its merger successor, the Penn Central, and in turn its freight railroad successor, Conrail.
Pennsylvania areas which are sometimes considered as distant suburbs or "exurbs" of Philadelphia include Berks County, the Lehigh Valley (Lehigh County and Northampton County), Lancaster County, and even the southern most region of the Poconos, including parts of Monroe County and Carbon County.
The Pennsylvania Turnpike bypasses the city a third of a mile north, and the New Jersey Turnpike, the main highway connection to New York City and points beyond, bypasses the city to the east and south.
In the east Pennsylvania is drained by the Delaware and the Susquehanna river systems; in the west by the Allegheny and the Monongahela rivers, which join at Pittsburgh to form the Ohio River; and in the central part by the West Branch of the Susquehanna, which crosses the state and empties into Chesapeake Bay.
Pennsylvania's population has grown slowly since the 1940s, when it was the second largest state in the union; it was the sixth most populous state after the 2000 census.
Although Pennsylvania is known as a coal state, mining only amounts to 0.6% of the state's economy, compared to 1.3% for the country as a whole.