Time was, trains were guided into South Station via hand-cranked levers

Thursday's South Station meltdown proved to be the fault of a computerized track-switching system in a building called Tower 1 (and seems Amtrak still is unsure what happened).

Today, Tower 1 is a shed, basically, but it once was an actual three-story tower in the middle of all the tracks funneling towards South Station. Installed in 1899, it handled the more than 700 trains that once came into and left the busiest train station in the country. Operators used hand-cranked levers to control pneumatic tubes that changed the settings of switches in the station's large "interlocking," where trains could be guided from one set of tracks to another.

In 1979, Tower 1 was put on the National Register of Historic Sites. And in 1983, with some of the original equipment still in operation, two historians documented the tower before Amtrak tore it down for replacement by a new computer-run system as part of the Northeast Corridor electrification project. Today, let's take a look at some of their photos (and tomorrow, we'll look at South Station back in the days when it was really big).

The tower:

There were a lot of levers:

A model atop the interlocking levers showed the switches in action:

The system also activated semaphores for train engineers:

The switches on the first floor that relayed electrical signals to the train switches:

Keeping track of those volts and amperes:

On the third floor, the supervisor could look out over the tracks:

More on the history of interlocking systems and South Station.