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Signal Aspects and Indications

 

Looking for information about the different "L" signaling types over the history of the system? See the "L" Signals: A Brief Overview and History page in the Infrastructure section.

The position of semaphore signals and specific combination of color-light aspects on wayside signals communicate vital operational instructions and track status to motormen and train operators to ensure safe movement and prevent collisions. Signal indications convey information that allow safe distances to be maintained between trains on the same track to prevent accidents, regulate speeds based on track conditions, upcoming curves, or the proximity of other trains, and routing information at junctions and crossovers. These indications have evolved over the years; below are a sample of CTA signal aspect and indication systems from different periods.

CTA Signal Aspects & Indications: November 1959

In November 1959, the CTA issued a pamphlet to operating employees about the meanings of different colored signals on the elevated system. The pamphlet had the following to say:

HIGH AND LOW INTERLOCKING HOME SIGNALS

Some Color Light Interlocking Home Signals are on high standards, one unit above the other; others are on low standards, one unit along side the other. Regardless of whether the signals are high or low, it is the position of one light above the other that governs the indication. On both types, the upper light indicates for the main route and the lower light indicates for the diverging route.

NUMBER PLATES ON COLOR LIGHT SIGNALS

The number plate on signals is considered part of the aspect.

a. "X" on a number plate indicates that a train may not proceed past a "stop" indication until further notice as been given.
 
b. Absence of an "X" on a number plate indicates that after making a stop at a "stop" indication, a train may proceed with caution past the "stop" indication.

NOTE: Illustrations of color light aspects in this folder do not indicate whether signals are high or low; they show the lights in relation to each other and the number plate.

Legend

Red signal

Amber signal

Green signal

Lunar white
signal

Flashing red
signal

Number plate
w/o an "X"

Number plate
w/an "X"

Interlocking Home Signals (Absolute Signals)

Normal Movement

Stop and stay.

(Where no towerman is on duty and signal fails to clear within 60 seconds, call Radio Dispatcher for instructions.)

Stop; operate Track Trip Manual Release. When trip clears, proceed with caution at restricted seed. (The Call-on Aspect)

Proceed with caution on main route, prepared to stop at next signal.

Proceed with caution on diverging route, prepared to stop at next signal.

Proceed on main route.

Proceed on diverging route.

Reverse Movement

Stop and stay.

Stop and stay.

Proceed with caution, prepared to stop within vision.

Automatic Block and Interlocking Approach Signals

Stop; operate Track Trip Manual Release. When trip clears, proceed with caution at restricted speed.

Proceed with caution prepared to stop at next signal.

Proceed.

Proceed with caution at or below allowable speed.

Special Aspects and Indications

North-South Route

Armitage Avenue, southbound

Proceed with caution on main route, at or below allowable speed.

17th Street, northbound

Proceed with caution on main route, at or below allowable speed.

13th Street, southbound

Proceed with caution into stub track prepared to stop within vision.

West-Northwest Route, Douglas Branch

Crossover east of 54th Avenue

Stop; proceed through crossover at restricted speed.

Crossover east of 54th Avenue

Proceed over normal route.

Thanks to Peter Christy for providing a copy of the pamphlet.

Chicago Transit Authority Rail System Rule Book: March 1985

Starting in October 1977, the CTA began issuing small rule books to its operating employees, listing regulations governing such things as General Information (uniforms, badges, etc.), Dealing with Passengers (fare collection, transfers, smoking rules, etc.), Equipment (lights, air comfort, etc.), Wayside Signals and Interlockings (definitions, aspects, etc.), and more. In the revision dated March 17, 1985, the section concerning signal aspects gives illustrations of typical elevated rapid transit wayside signals. The diagrams are mostly the same as in the 1959 pamphlet with only minor modifications.

The book gives the following signal diagrams:

Automatic Block and Interlocking Approach Signals

Stop.

Proceed expecting to encounter stop aspect at next signal.

Proceed.

Proceed expecting to encounter end of track or train ahead.

Proceed within permitted speed.

Interlocking Home Signals

Stop and stay.

Proceed on main route, expecting to encounter stop aspect at next signal.

Proceed on diverging route, expecting to encounter stop aspect at next signal.

Proceed on main route.

Proceed on diverging route.

Call-on: Stop; operate track trip manual release. When trip clears, proceed expecting to encounter end of track or train ahead.

Proceed on main route, expecting to encounter end of track or train ahead.

Proceed on diverging route, expecting to encounter end of track or train ahead.

Stop and stay.

Proceed on main route (to yard), expecting to encounter train ahead.

Proceed on diverging route (to Evanston), expecting to encounter train ahead.

Proceed on diverging route (to Skokie), expecting to encounter train ahead.

Reverse Movement Interlocking Home Signals

Stop and Stay.

Stop and stay.

Proceed expecting to encounter end of track or train ahead.