Operating "L" trains requires a complex and robust system of infrastructure to support it -- these include the track structures to support the tracks where they are elevated (perhaps the most identifiable character of Chicago's "L"), the track systems (rails, ties, etc.), the electrical system that powers the trains, signal systems that provide safe operation of trains, and more. The design of these infrastructure systems have developed and changed over time, reflecting both advances in technology and techniques, as well as experiences and preferences specific to the "L" system.

"L" Track Structures

The ABCs of Steel "L" Structure
An illustrated glossary of terms pertaining to the design and elements involved in trestle-type open-deck steel elevated railroad structures like the type the early "L" lines built.

Above All, there is the "L"!: Appreciating its Structure
By Stan Kaderbek and Art Peterson
An overview of steel elevated train structures in general, and the specific types and designs employed by the original "L" companies.

Above All, there is the "L"!: The Structure Adapts to Changing Conditions
By Stan Kaderbek and Art Peterson
Within the first decade of its existence, the early steel "L" structure had to adapt to changing conditions around it. This installment considers some of the changes that the structure has had to go through over the years, presenting them in the order in which they appeared on the scene.

"L" Signaling

Wayside Signals
Basic overview of wayside signals, which are any signal of fixed location along the tracks. These can include spacing boards, semaphores, automatic block signals with colored signal aspects (e.g. lights), and automatic train control (also with colored signals).

On the Matter of "L" Interlockings: Appreciating its Signals and Towers
By Kendrick Bisset and Art Peterson
Keeping trains safely separated from one another is essential to the operation of a densely-trafficked line or network of lines. This provides a basic overview of the concept of an interlocking -- an arrangement of signals that prevents conflicting movements through an arrangement of tracks such as junctions or crossings -- and four examples of interesting examples of "L" interlockings.

Trip Stop Story, Part 1: Migratory Patterns of "L" Track Trips
By Kendrick Bisset and Art Peterson
The "L" employs automatic track trips, which stop a train if it passes a red signal by causing an emergency brake application, at interlockings and certain other signals. This article explores the private "L" companies' early application of the devices.

Trip Stop Story, Part 2: Migratory Patterns of "L" Track Trips
By Kendrick Bisset and Art Peterson
Picking up where part 1 (above) left off, this article explores the evolution of track trips on the "L", including the change over from center trips to side trips.

For a list of towers and interlockings, see the Towers & Junctions section of the "L" Operations page.

Traction Power

Traction Power
An overview of how substations convert electricity from the local utility into the 600 volts that powers the "L", and of the design of the third rail shoes used on "L" trains.