CTA says this:
Q: I wanted to know about the smaller gauge tracks that are inside the regular tracks on some portions of the "L" . Were they old wide gauge tracks, then at some point the trains changed to standard gauge, but the old ones never removed? Or were they both used at the same time?
A: There are two types of those old rusty tracks you see inside and along "L" tracks.
The first type, which are seen on the North Side and Evanston Divisions, were separate tracks for freight operations. They are the same gauge as the "L" tracks, but are a second set of tracks offset from the "L" tracks by several inches. One track is between the "L" tracks and the other is outside the "L" tracks. They allow wider freight trains to clear the "L" platforms by creating a second set of tracks within what is essentially a single-track right-of-way. This is called a "gauntlet". These are no longer in use.
The second type has both rusty tracks between the "L" tracks. These rusty, usually grime covered rails are called "Guard Rails." They are to prevent a disaster in the event a train derails.
On a straight-away, whether a derailed truck goes off the running rails to the left or right, it can only move six to eight inches before the inner side of the wheel flanges contact the guard rails. So even though the wheels are bouncing on the ties, the derailed truck would not be able to swing left or right, far enough, to allow the train to go over the edge into the street, or cross over into an oncoming train. (And, just as important, the derailed truck would not be able to swing to the 70-90 degree point where it would break off under the car forcing equipment, mounted under the car, up through the car floor. Ghastly thought, no?)
On sharp curves, crossovers (switches), crossings, and interlockings, other types of guard rail technologies are used.
For example, on crossings and switch frogs the guard rail is typically a fabricated component of the running rail. The wheels ride on the outer rails, and there is a gap of several inches for the wheel flanges, then the inner rail. This virtually eliminates the chance of a derailment, while the truck is passing over the assembly. The straight-away type of guard rail is often used as an entry device, just before the switch or crossing, to guide a derailed truck to a more stabile position before it hits the points, frogs or crossing-track.
On very sharp curves, as in a CTA yard or in the Loop, yet another technique is used. On these tight curves the leading wheel of each truck will try to climb over the outside rail, no matter what speed the train is moving. This effect is especially pronounced if both the wheel flange and the rail are dry. Part of the solution is a contraption which may be called a "flange greaser." Just before the train enters one of these areas the wheels contact a pedestal along side the running rail. The pedestal operates a pump connected to a grease reservoir and as each wheel goes over the pedestal, a very small amount of grease is pumped out where the wheel flanges can pick up a little. So, over time, the grease migrates throughout the curve or interlocking track. This reduces the rail-climbing tendency, and has the secondary effect of reducing the volume of that earsplitting squeal as the train rounds the corners in the loop. This accounts for the amount of heavy black grease on the ties and guard rails one usually sees when you pass an interlocking plant.
(Thanks to retired-CTA worker Peter A. Christy [Badge #23234] for providing the answer to the second part of this question!)
