Originally, various track gauges were used in the United States. Some railways, primarily in the northeast, used standard gauge of 4 ft 8+1⁄2 in (1,435 mm); 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. The Pacific Railroad Acts of 1863 specified standard gauge be used for the first transcontinental railroad.
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.