A list of 3 ft 6 in (1,067 mm) gauge railways in the United States. Apart from historical railways, it is commonly used in underground coal mines.[1][2] Also, in the past, this gauge had been a popular choice for urban mass transit systems (see table below).
Pacific Electric (standard gauge lines and dual gauge lines with standard gauge track also present) (all 3 ft 6 in (1,067 mm) gauge trackage was dual-gauged with standard gauge trackage) (all dual gauge lines shared with Los Angeles Railway) (defunct)
Southern California Railway Museum (standard gauge lines, 3 ft (914 mm) gauge lines, and dual gauge lines with standard gauge track and 3 ft 6 in (1,067 mm) gauge track also present) (operating)