RAILROAD SIGNALS of the U.S.

A Primer on B&O CPL Signals

by Michael Watnoski
with help from

Todd Sestero
John V Engleman

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B&O Color Position Light signals, CPL's, are the most complete signal system used today.  This system is intuitive once you know the pattern.  It also conveys more information than other signal systems. At the bottom of the page, is a drawing showing the components of a fully loaded CPL signal.

Another unusual feature of this signaling system, is that CPL dwarf signals are capable of displaying all the aspects of a high signal, not just slow speed aspects as most other systems.

Speeds referred to in the CSX rulebook, which this discussion is based on, are as follows:  Limited - 45mph, Medium - 30mph, and Slow - 20mph.  Some of you may raise an eyebrow at the slow speed.  Yes, it was changed from 15!

A near complete CPL signal in south Baltimore
 

The main head displays the track occupancy for the selected route.  The B&O only used a two block system.  If the next two blocks beyond the signal were were clear (not occupied), the main head displayed a "high green" for "proceed".  When the second block was occupied, the head displayed yellow for "approach", preparing to stop at the next signal. Trains exceeding medium speed were required to slow to that speed.  If the block ahead of you was occupied, the signal displayed red for stop.

If the signal was an automatic, having a number board, then this was regarded as stop and proceed in the B&O days, and is now (under CSX), a restricted proceed.  Stop and proceed allowed the train to move, after stopping, at restricted speed (not exceeding 15 mph), prepared to stop within half the distance of sight, while watching for stopped trains, broken rail, or misaligned switches.  If the route is set for an un-signaled track, the restricting aspect, left diagonal lunar white lights, is used.  This requires the train to travel at restricted speed, as above.
 

The other six lights, or marker lamps, refer to the speed rating of the route being taken immediately beyond the signal and at the next signal.

Any light in the row above the main head indicates that route is going to be the main or high speed route beyond this signal.  This allows the train to proceed at track speed, as posted in the employee timetable for the territory, on green signals. 

The left and middle markers are white, the right marker is yellow.

All of the aspects in the photo to the left are for green signals.

There are two yellow aspects with a marker, and one red..... all use the middle marker. 

Rule C-285 is approach, preparing to stop at the next signal.  Rule C-286 is medium approach.... medium speed thru turnouts, etc, then proceed prepared to stop at the next signal.

The red aspect with a marker is rule C-291, restricted proceed, which the indication is the same for a restricting aspect - proceed at restricted speed. It has two variations, as shown to the left.   Many of you may be familiar with this aspect being called stop and proceed.  John adds, "during the gas shortage of the early to mid 70's, the B&O needed a way to to reduce costs, so they changed the rule to allow trains to keep rolling, looking for trains or problems ahead at no more than restricted speed".

Without any light above or below the main head, the train is going thru switches at slow speed, and must limit speed to 15 mph until the entire train is over the switches.  Obviously, there are three rules without markers lamps, and fall low in priority except for red, which is "at the bottom":

1) green for rule C-287A, slow-approach slow

2) yellow, rule C-288, slow-approach

3) red for rule C-292, which is stop

Rules 287A and 288 fall next to each other in priority, the only difference being 287A specifies going at slow speed to approach the next signal, while 288 says to prepare to stop at the next signal, but does not give a speed once thru the turnout.  Both mandate going at slow speed thru the turnout.

If lit, the row of markers below the main head indicates that train will be routed over switches at medium speed.  The train must reduce to medium speed, 30 mph, until all of it is passed through the switches, then it can proceed at the track speed set by the signal.  This is the typical indication when changing tracks at a crossover. 

Use of the lower markers specifies two speeds for the train.  One is the speed thru the turnout, which as stated above, is medium speed.  The other speed referenced is the speed of the train that is authorized once the entire train has cleared the turnout.  The speeds show up in the name of the aspect, such as: medium-approach slow or medium-approach medium.  The left marker signifies medium speed, the right marker slow, and the middle marker is unspecified (the rule just says "then proceed".

As above for the upper markers, the left and middle markers are white, the right marker is yellow.

CSX employs three flashing aspects, rules C-281B, approach limited; C-281C, limited clear; and C-287, slow clear.  The first two had flashing markers, 287 used a flashing green aspect without any markers.  It's interesting to note, if you look at the old versus the new rulebooks, that the B&O did not employ flashing aspects. 

CSX also slipped a new aspect in the books with the flashing green of rule C-287 (slow clear).  The solid green aspect that was formerly rule C-287, slow-approach slow, is now rule C-287A.

The two rules to the left, C281B (approach limited) and C281C (limited clear), could employ one of two methods to indicate the aspect.  One option is to use a flashing marker (without the yellow triangle), and the other is to use a steady marker, with a yellow triangle sign.

Rule 281B was previously rule C-282 under the B&O, and what is now 282, was 282A.  It's all very confusing!

This Drawing shows the major components of a full size B&O CPL signal.  As seen in the photos above, if left and/or right marker lamps are used, there are also two pieces of angle iron used to stabilize each marker, going from the marker to the pole, in addition to the cross pieces shown above.  A single 5" pole is used up to a height of 20 feet, above that, the pole starts out as a 6" pole at the bottom, and then reduces to 5".  Refer to the US&S drawings on another page.

John Engleman formerly worked for the B&O as an engineer (also for the Pennsy for a while prior to that, and was qualified on both).  His inputs have been invaluable in navigating thru some of the signal "urban legends" (and has some good stories to boot!).

Graphics and Pictures by Todd Sestero

MOD 10/6/06