Pittsburgh has more public staircases (737) than any other city in the United States, followed by [[Cincinnati]] and [[San Francisco]].ref Many of these staircases have [[street name]]s, and lead to hillside neighborhoods that can be difficult to access by car in winter.
== Tunnels ==
Notable tunnels include two interstate highway tunnels (both for [[I-376]]): [[Fort Pitt Tunnel]] and [[Squirrel Hill Tunnel]], major traffic tunnels: [[Armstrong Tunnel]] and [[Liberty Tunnels]], the lightrail tunnel: [[Mt. Washington Transit Tunnel]], and the [[Schenley Tunnel]], the [[Wabash Tunnel]] and [[Corliss Tunnel]].
== Railroads ==
During the heyday of the Steel industry, Pittsburgh was among the largest rail centers not only in the nation, but the world. For many years, the multiple rail crossings in the Pittsburgh suburb of [[...|Port Perry]] at the mouth of on the [[Monongahela River]] and adjacent to the [[Edgar Thomson Works]] and [[Duquesne, Pennsylvania|Duquesne mills]], was the highest concentration of freight traffic in the world. Even today, with river traffic included, Port Perry is often very near or at the top of the list. The [[Conway Yard]] to the west of the city along the [[Ohio River]] was the largest rail yard in the world from 1956 until 1980. From the beginning of the industrial era in America through its collapse in the 1980s, Pittsburgh was a key market for the nation's largest and most important railroads (most notably the Pennsylvania Railroad [the largest company in the world for much of the 20th century], but also for the New York Central [via the Pittsburgh & Lake Eire], Baltimore & Ohio and Pittsburgh & West Virginia). Despite the near complete collapse of heavy industry in the Northeast, Pittsburgh still remains an extremely important link in the nation's rail network, perhaps only second to Chicago.
Current railroads in Pittsburgh include: