Transportation in New York is made up of some of the most extensive and one of the oldest transportation infrastructures in the country. Engineering difficulties because of the terrain of New York State and the unique issues of New York City brought on by urban crowding have had to be overcome since the state was young. Population expansion of the state generally followed the path of the early waterways, first the Hudson River and then the Erie Canal. Today, railroad lines and the New York State Thruway follow the same general route.