Braking "suppression"

[Greg Gritton]

Some questions...


When a train equipped with cab signals passes a signal which
a more restrictive aspect than previous, and the train's speed
exceeds the speed associated with the new aspect, the engineer
must apply the brakes. However, is isn't clear to me how much
braking is required.


Some locomotives have a "temporary suppression" feature.
What does this do?


On ones that don't, it seems the engineer must move the
brake to a "suppression" level, which is called this as it
suppresses a penalty brake application. This is normally past
the full-service point on the brake handle. However, is isn't
clear to me whether this activates a full-service brake application
or something less. I have seen references to a 14 psi
reduction (about 1/2 of full-service) as well as ~26psi
reductions (full service). Does it vary by train?


Greg Gritto

[John Albert]

RE:
<< When a train equipped with cab signals passes a signal
which a more restrictive aspect than previous, and the
train's speed exceeds the speed associated with the new
aspect, the engineer must apply the brakes. However, is
isn't clear to me how much braking is required. >>

On Amtrak trains, full suppression requires a brake
reduction of approximately 17lbs. This is on AEM-7's. On
HHP's and the Acela trainsets, the suppression position on
the brake valve seems to produce just a couple of pounds
more. I believe the brake equipment on the Genesis engines
(which I don't spend time on anymore) is about the same.

On the Conrail freight locomotives I _used to_ work on, you
had to go just past "full service" in the brake quadrant to
achieve suppression (on a 90lb. brake pipe, this would be a
little over 26lbs.). But bear in mind that freight
locomotives do not used air-based speed control - or that is
to say, Conrail didn't use it. The engines had cab signals
and an automatic train stop feature, but once the cab signal
changed and the audible indicator was acknowledged, the
engineman had the freedom to get the train speed under
control in any way he wished.

When the "LSL's" came in later, they didn't use "air-based
speed control", either. When the cab signal changed, you
were on your own to take whatever action you preferred to
bring the speed down, so long as it was done within a
certain time frame. Exceed that time frame, and you'd get a
penalty.

I don't know what freight engines are using for speed
enforcement these days, whether the CSX engines in service
on the Corridor still use the LSL's or not.

Actually, I don't think any major railroad in the country
uses speed control on freight trains, outside of the
Northeast Corridor. The last thing you want with a heavy
freight train a mile and a half long is to take control of
the brakes away from the guy running it!

Metro-North M-series equipment uses an "Automatic Train
Control" system that is completely the opposite of the
freight philosophy. When the cab signals change on the
M-cars, the train automatically goes into "max brake"
(equivalent of full service) regardless of what the
engineman does. Once the train has reduced to a speed
conforming to the cab signal, the engineman can get a
release by acknowledging the audible indicator, placing the
control handle into "Max brake", and then releasing. That's
the way it was when I worked there; it's been 25 years but
I'll bet the equipment still works [nearly] the same way.

- John

[Greg Gritton]

Hello John,

On Amtrak trains, full suppression requires a brake reduction of
approximately 17lbs. This is on AEM-7's. On HHP's and the Acela
trainsets, the suppression position on the brake valve seems to
produce just a couple of pounds more. I believe the brake equipment on
the Genesis engines (which I don't spend time on anymore) is about the
same.

Is a 17lb brake application enough to stop a train in time for a
red signal or slow down for a diverging route if the train enters
the block at full track speed?

Greg Gritto

[o u t e n d]

Actually, I don't think any major railroad in the country uses speed
control on freight trains, outside of the Northeast Corridor. The last
thing you want with a heavy freight train a mile and a half long is to
take control of the brakes away from the guy running it!

Norfolk Southern has 6 former Conrail GP40-2's (3065-3070) equipped with
ITCS for use between Kalamazoo and Niles, Michigan. The only freight
traffic over the Amtrak Michigan Line is local switching. Train lengths
are relatively short. ITCS does speed enforcement.

NS just recently tried to unload their Michigan Line but the STB
interestingly enough denied it. The STB stated that NS was at the same
time giving up the line while maintaining almost total control over it. To
me and others, it was just a union busting move.

[Bill Blomgren]

Post by o u t e n d

Actually, I don't think any major railroad in the country uses speed
control on freight trains, outside of the Northeast Corridor. The last
thing you want with a heavy freight train a mile and a half long is to
take control of the brakes away from the guy running it!

Norfolk Southern has 6 former Conrail GP40-2's (3065-3070) equipped with
ITCS for use between Kalamazoo and Niles, Michigan. The only freight
traffic over the Amtrak Michigan Line is local switching. Train lengths
are relatively short. ITCS does speed enforcement.
NS just recently tried to unload their Michigan Line but the STB
interestingly enough denied it. The STB stated that NS was at the same
time giving up the line while maintaining almost total control over it. To
me and others, it was just a union busting move.

Well, if they get serious about it, they can simply reduce service, and then
file for abandonment, leaving it to the state and or Amtrak to buy it. Of
course, then they would have *no* control over the line at all.

[James Robinson]

Post by John Albert
Actually, I don't think any major railroad in the country
uses speed control on freight trains, outside of the
Northeast Corridor. The last thing you want with a heavy
freight train a mile and a half long is to take control of
the brakes away from the guy running it!

The only other major installations of cab signaling are the commuter
zones in Chicago, and parts of the C&NW/UP Overland Route. In both
cases, they have historically enforced speeds with the pneumatic
overspeed control, so a suppression brake was required to avoid the
penalty application.

The ex-C&NW lines in the commuter zone, as an example, have a two aspect
CCS system, which only displays clear or restricting aspects. The only
wayside signals are the approach to interlockings, and at the
interlockings themselves. Intermediates are handled by the cab signal
system, with no accompanying wayside signal. This arrangement allows
non-equipped locomotives to operate over the route under absolute blocks
between interlockings.

If a train passes other than a clear signal, a two-stage speed
enforcement is initiated. The train is given a certain amount of time to
get first to 40 mph (IIRC), then some additional time to get below 20
mph. Failure to get below the appropiate speed will initiate a penalty
brake sequence of warning whistle, delay, penalty. The penalty can be
suppressed.

Depending on how fast the train is operating, it might require a light or
heavy brake application to get to the required speed.