Saturday, March 31, 2012

the hump

Freight yards like Chicago & North Western's at Proviso contain hundreds of parallel tracks. These permit arriving trains to be broken up so that individual cars can be grouped by their destinations. Some freight trains — such as those which carry coal from mines to power plants — can remain intact throughout their journey. However most contain isolated cars that are only generally headed in the right direction. These have to be reassembled one or more times along their route as they draw closer to the yards where they will be unloaded. This reassembly is accomplished by shunting cars on the parallel tracks in yards like the one at Proviso.

The shunting takes place in classification yards. The aerial photo I showed the other day gives an idea of the shape and extent of the C&NW yards circa 1940. This is a detail from that image in which you can see the track layout.
{Detail from photos of the 1938-1941 Aerial Survey of Illinois; source:
Illinois Aerial Photos.[1]}

This photo shows portions of two of the C&NW's "ladders" — the sets of parallel tracks into which cars would be shunted. As in my previous post, it was taken for the Office of War Information by staff photographer Jack Delano and is found in collections of the Prints and Photographs Division, Library of Congress. Notice that, as you'd expect, each pair of tracks splits from a main feeder and each has its own switch. The feeder is called a lead or drill.

{Caption: General view of one of the Chicago and Northwestern railroad classification yards, Chicago, Ill. December 1942}

This shows a switchman in the act of shunting some cars. Delano took this in April 1943.[2]

{Caption: Switchman throwing a switch at C&NW RR's Proviso yard, Chicago, Ill. 1942 Dec.}

The C&NW yards received lists via teletype showing the makeup of arriving trains and the destinations of their cars. These switch lists enabled workers such as the one shown below to map out the distribution of cars in the classification yards. The mapping is a lot easier to explain than it was to carry out in a place the size of proviso with its hundreds of switches.[3]

{Caption: Switch lists coming in by teletype to the hump office at a Chicago and Northwestern railroad yard, Chicago, Ill. 1942 Dec. }

Cars would be pushed around the yards by shunt engines and in large facilities like the one at Proviso they might also be fed to the ladders by gravity. Locomotives would push a train up a gentle incline, called a hump, and the cars would be released to roll down the lead toward the switches.

This photo shows one of the humps at the C&NW yards. A tank car has just been uncoupled and is making its way down the hump toward the ladders.

{Caption: General view of one of the yards of the Chicago and Northwestern railroad, Chicago, Ill. 1942 Dec.}

This shows a shunt engine working on a lead. You can see two towers where towermen controlled the flow of cars from the hump down the lead and into the ladders.

{General view of the hump, Chicago and Northwestern railroad classification yard, Chicago, Ill. 1942 Dec.}

In this view of the same set of ladders you can see the downslope from the hump at the foot of the foreground tower.

{General view of the hump yard at Proviso yard, C&NW RR., Chicago, Ill. 1942 Dec.}

The caption explains this photo. The hump track to which it refers is continued by the lead or drill.

{Hump master in a Chicago and Northwestern railroad yard operating a signal switch system which extends the length of the hump track. He is thus able to control movements of locomotives pushing the train over the hump from his post at the hump office; Chicago, Ill. 1942 Dec.}

There were devices called retarders on the lead tracks. These were electrically controlled and could be used to slow down cars as they descended from the hump. Switches could also be electrically operated. This towerman is shown at the retarder and switch controls.[4]

{C&NWRR, towerman R.W. Mayberry of Elmhurst, Ill., at the Proviso yard. He operates a set of retarders and switches at the hump, Melrose Park (near Chicago), Ill. 1943 May}

I think Delano took this shot from one of the towers.

{Caption: General view of one of the yards of the Chicago and Northwestern railroad, Chicago, Ill. 1942, Dec.}


Some sources:

"Combination Through Classification and Terminal Yard" by W.C. Copley in Railway age Vol. 58 (Simmons-Boardman Publishing Corp., 1915)

Classification yard on wikipedia

Retarder on wikipedia

Switcher on wikipedia

Shunt (rail) on wikipedia

Train shunting puzzles on wikipedia



[1] This larger detail shows the complex interconnection of the classification yards the Proviso facility. Click to view full size.

[2] Jack Delano took all the images on this page on assignment from OWI in December 1942 and April 1943 and all are from collections of the Library of Congress.

[3] Railroaders have train shunting puzzles which are games that challenge players to break up and reassemble trains (called consists) with a minimum of de-couplings and couplings.

[4] This view of a classification yard (not C&NW) shows retarders on the leads just before the ladders. I've marked two of them with yellow circles.

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