Five foot two and a half inch gauge railways

Originally, various gauges were used in the United States. Some railways, primarily in the northeast, used standard gauge; others used gauges ranging from 2 ft (610 mm) to 6 ft (1,829 mm). As a general rule, southern railroads were built to one or another broad gauge, mostly 5 ft (1,524 mm), while northern railroads that were not standard-gauge tended to be narrow-gauge.

Notable exceptions were the 6 ft (1,829 mm) railroads that predominated in the first part of the 19th Century in New York State, and the 5 ft 6 in (1,676 mm) lines centered on Portland (Maine). Problems began as soon as lines began to meet and in much of the north-eastern United States, standard gauge was adopted. Non-standard gauges remain in use for some municipal and regional mass transit systems not requiring interchange of equipment.

The New York and Erie Railroad was originally 6 ft (1,829 mm) gauge, and spawned a regional network of other six foot gauge railroads within New York State. Chartered in 1832, its first section opening in 1841, the Erie's promoters and early engineers believed it would be so busy that wider gauged tracks would be required for locomotives much larger (and therefore more powerful) than usual to pull the expected very long and heavy trains. 6 ft gauge was also cited for improved stability, and the New York and Erie eventually had rolling stock with 11 feet (3.35 m) wide loading gauge. Other railroads connecting to the Erie were soon built, able to interchange freight and passenger cars, forming a true regional six foot gauged railroad network across southern tier of New York State from the Hudson River to the shores of Lake Erie.

Major cities including Rochester, Syracuse, Utica, and Albany all were connected by six foot gauged railroads extending from Elmira and Binghamton on the New York and Erie mainline. These lines included the Avon, Genesee & Mt. Morris, the Albany and Susquehanna (later part of the Delaware and Hudson), the Elmira, Jefferson & Canandaigua (later the Northern Central, becoming part of the Pennsylvania Railroad), the Rochester & Genesee Valley, the Canandaigua and Niagara Falls (initially Erie controlled, later part of the New York Central railroad's Peanut Route along the shoreline of Lake Ontario), and even the mainline of rival, and future (1960) merger partner, the Delaware, Lackawanna, and Western (The Lackawanna also had a significant portion of its six-foot gauge trackage in Pennsylvania and New Jersey). Other 6 ft gauge lines included the Syracuse, Binghamton & New York (later part of the Lackwanna), the Walkill Valley railroad (later part of the New York Central), and the Erie's own Newburgh branch. Between 1876 and 1880 most of the 6 ft lines converted to standard gauge, some having been first dual gauged with a third running rail allowing standard gauge trains to share the track, prior to the removal of the 6 ft rails.

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