Capitol, North O Street and South Washington Railway

The Capitol, North O Street and South Washington Railway (later, the Belt Railway) was a street railway company in Washington, D.C., from 1875 to 1898. It was the sixth and final company to start during the horse car era. It operated on a loop, or "belt," around downtown and the National Mall. For that reason, and because of its long name, it was known colloquially as the Belt Railway. It formally changed its name to the Belt Railway in 1893. It expanded north on 11th Street NW to the city's then-boundary and south to river waters. In 1896, company officials attempted to use compressed air motors instead of electricity to power their streetcars, a decision that sent them into receivership. In 1898, the company was purchased and absorbed by the Anacostia and Potomac River Railroad.

Origins
The Capitol, North O Street and South Washington Railway Company was the last streetcar company to begin operations during Washington's horsecar era. It was incorporated on March 3, 1875, and began operation later that year. Its circular route went from the Capitol along 1st Street SW; south of the Mall on Maryland and Virginia Avenues SW; north on 12th Street SW/NW, the old Ohio Avenue NW (now obliterated by Federal Triangle) and 14th Street NW to O Street NW; east on O Street NW for ten blocks; and then south on 4th Street NW, G Street NW and 1st Street NW.

Expansion and name change
The Capitol, North O Street and South Washington went through several changes after its initial startup. A P Street NW track was added in 1876 for westbound cars, leaving O Street NW for eastbound traffic. In 1881, the 11th street line was extended north to Boundary Street and south to Water Street SW and along that street to the Arsenal. At the same time, tracks were rerouted across the Mall. The last change came on February 18, 1893, when it changed its name to the Belt Railway Company.

Switch to electricity
In 1896, Congress directed the Belt Railway to try out compressed air motors, just as it had the Eckington and Soldiers' Home Railway. The compressed air motors were a failure. In 1899, the company's cars were equipped with the city's standard underground power system.

Bankruptcy and purchase
As a result of the compressed air motor fiasco, the company went into receivership. Shortly thereafter, on June 24, 1898, the Anacostia and Potomac River purchased the Belt Railway.