The Hudson River is navigable for a great distance above mile 0 (at 40°42.1'N., 74°01.5'W.) off The Battery. The original Erie Canal, opened in 1825 to connect the Hudson with Lake Erie, emptied into the Hudson at the Albany Basin, just three miles (5 km) south of the Federal Dam in Troy (at mile 134). The canal enabled shipping between cities on the Great Lakes and Europe via the Atlantic Ocean. The New York State Canal System, the successor to the Erie Canal, runs into the Hudson River north of Troy and uses the Federal Dam as the Lock 1 and natural waterways whenever possible. The first railroad in New York, the Mohawk and Hudson Railroad, opened in 1831 between Albany and Schenectady on the Mohawk River, enabling passengers to bypass the slowest part of the Erie Canal.
In northern Troy, the Champlain Canal split from the Erie Canal and continued north along the west side of the Hudson to Thomson, where it crossed to the east side. At Fort Edward the canal left the Hudson, heading northeast to Lake Champlain. A barge canal now splits from the Hudson at that point, taking roughly the same route (also parallel to the Delaware and Hudson Railway's Saratoga and Whitehall Railroad) to Lake Champlain at Whitehall. From Lake Champlain, boats can continue north into Canada to the Saint Lawrence Seaway.
The Hudson Valley also proved attractive for railroads, once technology progressed to the point where it was feasible to construct the required bridges over tributaries. The Troy and Greenbush Railroad was chartered in 1845 and opened that same year, running a short distance on the east side between Troy and Greenbush (east of Albany). The Hudson River Railroad was chartered the next year as a continuation of the Troy and Greenbush south to New York City, and was completed in 1851. In 1866 the Hudson River Bridge opened over the river between Greenbush and Albany, enabling through traffic between the Hudson River Railroad and the New York Central Railroad west to Buffalo. When the Poughkeepsie Rail Bridge opened in 1889, it became the longest single span bridge in the world. On October 3, 2009, it re-opened as a pedestrian walkway over the Hudson, as part of the Hudson River Quadricentennial Celebrations and connects over 25 miles of existing pedestrian trails.
The New York, West Shore and Buffalo Railway began at Weehawken Terminal and ran up the west shore of the Hudson as a competitor to the merged New York Central and Hudson River Railroad. Construction was slow, and was finally completed in 1884; the New York Central purchased the line the next year.
The Hudson is crossed at numerous points by bridges, tunnels, and ferries. The width of the Lower Hudson River required major feats of engineering to cross, the results today visible in the Verrazano-Narrows Bridge, the George Washington Bridge, and the Tappan Zee Bridge, as well as the Lincoln and Holland Tunnels and the PATH and Pennsylvania Railroad tubes. The George Washington Bridge (signed as I-95/US 1-9/US 46), connecting Fort Lee, New Jersey to the Washington Heights neighborhood of Upper Manhattan in New York City, is the world's busiest motor vehicle bridge. The Troy-Waterford Bridge at Waterford was the first bridge over the Hudson, opened in 1809. The Rensselaer and Saratoga Railroad was chartered in 1832 and opened in 1835, including the Green Island Bridge, the first bridge over the Hudson south of the Federal Dam.
The Upper Hudson River Valley was also useful for railroads. Sections of the Rensselaer and Saratoga Railroad, Troy and Boston Railroad and Albany Northern Railroad ran next to the Hudson between Troy and Mechanicville. North of Mechanicville the shore was bare until Glens Falls, where the short Glens Falls Railroad ran along the east shore. At Glens Falls the Hudson turns west to Corinth before continuing north; at Corinth the Adirondack Railway begins to run along the Hudson's west bank. The original Adirondack Railway opened by 1871, ending at North Creek along the river. In World War II an extension opened to Tahawus, the site of valuable iron and titanium mines. The extension continued along the Hudson River into Hamilton County, and then continued north where the Hudson makes a turn to the west, crossing the Hudson and running along the west shore of the Boreas River. South of Tahawus the route returned to the east shore of the Hudson the rest of the way to its terminus.
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