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.
Portland gauge of 5 ft 6 in (1,676 mm) was used on the Grand Trunk Railway, Maine Central Railroad, and a system of connecting lines to funnel interior traffic through the port of Portland, Maine, in competition with the standard gauge railway system serving the port of Boston. The Portland Company was formed to build locomotives of this gauge for use on the local rail system. The gauge was known as "Texas gauge" while required by Texas law until 1875, and used by the New Orleans, Opelousas and Great Western Railroad (NOO&GW) until 1872, and by the Texas and New Orleans Railroad until 1876. The New England railways were similarly standard-gauged in the 1870s.
In the 1960s, the gauge was selected for use in the Bay Area Rapid Transit system, serving the San Francisco Bay Area; it is the only place in the United States where this gauge is in use. The rapid transit segment of the system covers 109 miles (175 km) of double track in revenue service.
5 ft 2 1⁄4 in (1,581 mm) and 5 ft 2 1⁄2 in (1,588 mm) are commonly known as Pennsylvania trolley gauge because it was originally used by railroad lines in the state of Pennsylvania. Unlike other broad gauges, it remains in use in a number of urban rail transit systems:
In most of the southern states, the 5 ft (1,524 mm) gauge was preferred (a broad gauge which later was adopted by Russia for its new railroad and became known as Russian gauge). This configuration allowed for wider rolling stock that could more efficiently accommodate cotton bales, the most commonly transported good in the South at the time. In the U. S. this gauge was changed to 4 ft 9 in (1,448 mm) in 1886.
Most of the original track in Ohio was built in 4 ft 10 in (1,473 mm) gauge, the "Ohio Gauge".
The world's first operational mountain-climbing cog railway (rack-and-pinion railway), the Mount Washington Cog Railway in Coos County, New Hampshire — in operation since its opening in 1869 — uses a 4 ft 8 inch (1,422 mm) rail gauge, as designed by Sylvester Marsh, the creator of the Marsh rack system for ensuring firm traction going up and down the slopes of the highest mountain in New England.
The San Francisco cable cars use the Cape Gauge of 3 ft 6 in (1,067 mm), as did the Los Angeles Railway and the San Diego Electric Railway until 1898, and that gauge is still widely used in the U.S. mining industry.
3 ft (914 mm) gauge railways became the dominant narrow gauge throughout the United States from the Boston, Revere Beach and Lynn Railroad of Massachusetts to the Pacific Coast Railway of California. The gauge was also used by the Oahu Railway and Land Company of Hawaii and the White Pass and Yukon Route of Alaska. Heritage railroads operate portions of the formerly extensive Colorado system as the Durango and Silverton Narrow Gauge Railroad and Cumbres and Toltec Scenic Railroad.
The Angels Flight and Court Flight funicular railways of Los Angeles used 2 ft 6 in (762 mm). The gauge was also used for the Yosemite Short Line Railway, the Pacific Coast Steamship Company's horse-powered tramway near Pismo Beach, California, Michigan's Harbor Springs Railway, and several Hawaiian sugar plantation railways. This became a popular gauge for heritage railways in California, Florida, Hawaii, Minnesota, Montana, Nebraska, Oregon, and Pennsylvania.
Several Maine railroads used 2 ft (610 mm) gauge following demonstration on the Billerica and Bedford Railroad in 1877, including the Sandy River and Rangeley Lakes Railroad, the Wiscasset, Waterville and Farmington Railway, the Kennebec Central, the Monson Railroad, and the Saco Biddeford & Harrison (later the Biddeford & Harrison). When these railroads ceased operation in the 1940s, their equipment was transferred to the Edaville Railroad, which remains in operation as one of the oldest American heritage railroads. The gauge was also used by the Mount Gretna Narrow Gauge Railway, and by some mining railways of the Rocky Mountains. Similar 600 mm (1 ft 11 5⁄8 in) gauge equipment manufactured for the trench railways of World War I was used on United States military bases in Alabama, Georgia, Indiana, New Jersey, and Oklahoma through World War II; and sold as military surplus for earth-moving construction through the 1920s.
In the early days of rail transport in the United States, railroads tended to be built out of coastal cities into the hinterland, and systems did not connect. Each builder was free to choose its own gauge, although the availability of British-built locomotives encouraged some railroads to be built to standard gauge.
When American railroads' track extended to the point that they began to interconnect, it became clear that a single nationwide gauge would be a good idea.
Where different gauges meet, there is a "break of gauge". To overcome this issue, special compromise cars were able to run 4 ft 10 in (1,473 mm) and standard gauge track. Another application was the Ramsey car-transfer apparatus.
In Erie, Pennsylvania, the 6 ft (1,829 mm) Erie Railroad terminated while adjacent railroads used 4 ft 10 in (1,473 mm) gauge, also known as "Ohio gauge." This led to the Erie Gauge War in 1853-54 when the Erie mayor and citizens temporarily prevented a gauge standardization, as there would then be less trans-shipping work and through passengers would no longer have a stopover at Erie.
Break of gauge would prove to be a nightmare during the American Civil War (1861–1865), often hindering the Confederacy's ability to move goods efficiently over long distances. The Pacific Railway Act of March 3, 1863, specified that the federally funded transcontinental railroad was to use standard gauge and helped to further popularize it among American railroads, although the standard gauge was already in use on many other lines prior to 1863.
Following the Civil War, trade between the South and North grew sufficiently large that the break of gauge became a major economic nuisance, impeding through shipments. Competitive pressures induced most North American railways to convert to standard gauge by 1880, but Southern railroads remained on its distinct, 5 ft. (1,524 mm) gauge. In 1884 and 1885, two important railroads connecting Chicago to the South (the Illinois Central and the Mobile and Ohio Railroad) converted to standard gauge, increasing pressure on competing and connecting lines to do the same.
In 1886, the southern railroads agreed to coordinate changing gauge on all their tracks. After considerable debate and planning, most of the southern rail network was converted from 5 ft (1,524 mm) gauge to 4 ft 9 in (1,448 mm) gauge, then the standard of the Pennsylvania Railroad, over two remarkable days beginning on Monday, May 31, 1886. Over a period of 36 hours, tens of thousands of workers pulled the spikes from the west rail of all the broad gauge lines in the South, moved them 3 in (76 mm) east and spiked them back in place. The new gauge was close enough that standard gauge equipment could run on it without problem. By June 1886, all major railroads in North America, an estimated 11,500 miles (18,500 km), were using approximately the same gauge. To facilitate the change, the inside spikes had been hammered into place at the new gauge in advance of the change. Rolling stock too was altered to fit the new gauge at shops and rendezvous points throughout the South. The final conversion to true standard gauge took place gradually as track was maintained. Now, the only broad-gauge rail systems in the United States are some city transit systems.
Using historical freight traffic records, recent research has shown that the conversion to standard gauge instigated a large shift of North–South freight traffic away from coastal steamships to all-rail carriage. These effects were especially strong on short routes, where breaks in gauge were more expensive relative to the total cost and duration of carriage. However, the data indicate that the gauge change had no effect on total shipments, likely as a result of anticompetitive conduct by Southern freight carriers which prevented the railroads' cost-savings from being passed through to their prices. This research suggests that had Southern carriers not been colluding, the gauge change would have generated a sharp reduction in freight rates and immediate growth in trade between the North and South.
Worst of all, not all city systems were built to the standard American and European gauge of 4'-8 1⁄2". Pittsburgh and most other Pennsylvania cities used 5'-2 1⁄2", which became known as the Pennsylvania trolley gauge. Cincinnati used 5'-2 1⁄2", Philadelphia 5'-2 1⁄4", Columbus 5'-2", Altoona 5'-3", Louisville and Camden 5'-0", Canton and Pueblo 4'-0", Denver, Tacoma, and Los Angeles 3'-6", Toronto an odd 4'-10 7⁄8", and Baltimore a vast 5'-4 1⁄2".