Eastern Railroad Discussion > How do Cab Signal systems work?

How do Cab Signal systems work from the engineer’s point of view? How do you interact with the system? As you approach a signal I assume that signal aspect is displayed in the cab. Does the system warn (predictivily) or beep as you approach a “Stop” signal? When does the system enforce/apply the brakes on a train? Can you override this enforcement? If a dispatcher talks you past a red signal are you able to acknowledge the red signal without enforcement?


I know there are numerous different Cab Signal system running so if you have any commits please tell me what railroad they refer too and the name of the system if you know.

Thanks
Kevin

Cab signals are simply a system that displays signal aspects inside the locomotive cab, either in supplement to or in the place of wayside signals. The cab-signal device itself does not have any built-in enforcement capabilities. Such capability is vested in devices most commonly known as Locomotive Speed Limiters, which activate the brakes automatically in a "penalty application" if the train operator does not respond promptly to a signal display requiring a reduced speed. I do believe that cab signals, with or without LSL, have audible alarms when a reduced aspect is first displayed. However, there is no "Stop" signal aspect to cab signals or LSL operation -- the most restrictive aspect applied by those systems is "Restricting," which typically has a maximum of 15 mph. So the LSL device does not prevent a train from passing a Stop signal with the dispatcher's permission (or even without it, as long as the engineer first reduces to restricted speed).

DISCLAIMER
This is my understanding of how these systems work, based on having ridden on the head-ends of several trains in the Northeast Corridor. Specifics of systems elsewhere in the country may differ. Your mileage may vary. I am not a railroad engineer or signal maintainer, nor did I stay in a Holiday Inn Express last night. All rights reserved, all wrongs corrected. The Surgeon General has warned that cigarette smoking may cause birth defects.

Also, an unintentional penalty application can be suppresed if you place the throttle in idle and set the brake lever to suppresion for twenty (?) seconds. With luck you'll not come to a complete stop, but have to be careful not to pull the train in two by not waiting on a decent release. I have had more than one motor that would throw a penalty for no reason, and used that method to recover and keep going.

An electronic code is transmitted down the rails. A receiver mounted on the front of the locomotive receives this code and displays the approiate signal display in the locomotive. If the system is set up for automatic train control (as in the former RF&P system) it will dump the train in emergency if the Engineer doesn't respond approiately.

It does not Dump the air, it gives a Full service Brake reduction.

wm82engineer Wrote:
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> An electronic code is transmitted down the rails.
> A receiver mounted on the front of the locomotive
> receives this code and displays the approiate
> signal display in the locomotive. If the system is
> set up for automatic train control (as in the
> former RF&P system) it will dump the train in
> emergency if the Engineer doesn't respond
> approiately.

No it will not be an emergency application, they are potentially wreck causing, and ONLY for emergency or train separation (where it becomes automatic) A Cab signal or alerter penalty applies the brakes at service rate, and does not draw them below the point where an emergency app could be made (Lower than 45 psi brake pipe)Further if it were an emergency app then the suppresion feature would not work.

Most cab signals territory's that I have ridden on do not show the signal aspect IN ADVANCE. They only show the aspect of the block the train is currently in. If a train where running on a yellow signal in heavy fog and is approaching a red signal the cab signal is still showing yellow, up and to the point the receiver on the loco enters the red block -- which would be a few seconds after passing the physical red signal. If the engineer never saw the red in this example due to fog, the cab signal now allerts the engineer that he is in a red block.

Cameraman Wrote:
-------------------------------------------------------
> Most cab signals territory's that I have ridden on
> do not show the signal aspect IN ADVANCE. They
> only show the aspect of the block the train is
> currently in. If a train where running on a yellow
> signal in heavy fog and is approaching a red
> signal the cab signal is still showing yellow, up
> and to the point the receiver on the loco enters
> the red block -- which would be a few seconds
> after passing the physical red signal. If the
> engineer never saw the red in this example due to
> fog, the cab signal now allerts the engineer that
> he is in a red block.

The PRR/CR/NS (and as far as I know, Amtrak) does change over from Approach to Restricting before reaching the upcoming wayside Stop Signal. In most instances, the CS system "drops" to restricting about halfway between the wayside Approach, and the upcoming Stop.

This changeover only occurs in advance of a Rule 292 STOP signal, not STOP and PROCEED. At some places in the NEC Amtrak has implemented a poor man's 4-block signaling system using intermediate cut points to drop signals to APPROACH MEDIUM in advance of an APPROACH where the stopping distance is too short.

The "standard" cab signal system as marketed by US&S and adopted by the PRR/PC/CR/NS/Amtrak/MNRR/LIAR/RF&P/CB&Q uses coded track circuts.

In lineside cabinets there are a number of code generators (see photo) that sent pulses of current through the rails to be picked up by an induction reciever on the pilot of the locomotive.

Codes are generated in advance of the train and reflect the state of the block the train is currently in.

Codes can change (upgrade of downgrade) while the train is between blocks and the train needs to respond accordingly. When a cab signal is not in conformance with a wayside signal, the most restrictive indication rules.

Codes are "eaten" up by the short circut caused by the trains wheels in the block so following movements do not get the leading movement's code. Single unit MUs or other short trains require protection to the rear in cab signal territory.

The "standard" form of cab signal has 4 aspects. RESTRICTING = 0 Pulses Per Minute APPROACH = 75 PPM, APPROACH MEDIUM = 120 PPM , CLEAR = 180 PPM. The LIRR uses two extra codes, 270 and 420, for clear block speed codes of 55/60 and 65/60. Amtrak is also adding a number of new codes including APPROACH MEDIUM 30, APPROACH LIMITED 45, CAB SPEED 60, CAB SPEED 80, CLEAR 100 and CLEAR 150.

Back in the day US&S marketed a "loop" cab signal system, but I have never fond anyone to explain how that system worked.

Out west UP and the IC use/used a 2 aspect system that displayed CLEAR and RESTRICTING aspects only. The UP has expanded it's cab signaling system, including stretches without wayside signals, but I am unsure how this system works and how many aspects it uses.

There are all sorts of quirks and details with the systems, especially when you get into the realm of speed control, but this is how things generally work.

A note about speed control, except on east coast passenger lines, freight trains do not operate with cab signal speed control systems. In fact on the RF&P a speed control cannot be used as there are specific times when your cab drops to restricting out and wayside aspects govern.

I hope I was able to answer your question.

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I pulled out my color orginal copy of the GRS Coded Cab Signal Bulletin 171. dated October 1937 GRS=General Railway Signal Company of Rochester, N.Y.

Pictures show the best location of the cab signal in the cab of New York, New Haven and Harford Locomotive (2-3-2). Part of the external equipment is shown mounted on the Tender of N.Y.N.H.&H installation. The view was from the top rear of the water tank into the coal filled bin

The San Fancisco, Oakland Bay Bridge is shown on one page. A picture of a cab signal installed on electric transit cars used on the Bay Bridge is shown on page 12.

I have operated during bad weather in cab sig territory during emergency situations and it sure was nice to know where in the night snow filled right of way where and what your signals were.