Can locomotives be so peppy that any overspeed controls would render them useless?
This is kind of related to the Amtrak 188 wreck at Frankford Junction Philly. If I remember correctly the train didn't start speeding until near the end of 80mph territory going into 50mph territory and finished at over 100mph. It also seems to me that it traveled a relatively short distance to accelerate those 20 or so mph, when it should have decelerated about 30 or so mph.
I've also read some posts that said although Frankford Junction curve's speed limit is 50mph that it's possible to traverse it at 80mph without derailing.
Is the ACS64 so poweful that it could have accelerated from 50 to 80+mph so fast that an overspeed control would not have slowed it in time?
Of course I may be way off on my numbers in this case, but in any case it seems to me that it's possible to have a locomotive whose accelration is so good, and some speed limits so restrictive, that no overspeed control would be worthwhile. Also of course there are some whose opinion is that Positive Train Control's cost-benefit ratio makes it not worthwhile either.
Patrick Boylan
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This seems kind of like asking "If I floor the gas pedal in my car and stand on the brake at the same time, what happens ?"
Does your question presume that the overspeed control would only apply the brakes, and not cut off traction power to the locomotive ?
On most diesels, when the train goes into emergency, there's an automatic cut-off of power - except when it's in dynamic braking mode, such as holding the train back on a descending grade, and then leaving the power on to continue the braking is only a good thing.
Most diesels - even on a lightweight passenger train - no, I'd think.
A high-horsepower electric with unlimited power from the catenary, substantial short-term overload rating, and acceleration capability ? Perhaps. But if the trailing cars weigh as much as the locomotive (or maybe 35%/ 25% = 1.4 times as much), their braking ability will be more than a match for the locomotive's adhesion and tractive effort. As soon as the train brakes are fully applied on 2 or 3 cars- a second or two at most for a short train, maybe another second for a longer one - the cars will start to drag on the locomotive and slow it down, causing the loco to slip its wheels, even at max. power and with super-adhesion conntrols (see the 35% above). It would be kind of like a 'tractor pull', where the sled load gets progressively harder to pull as the tractor goes farther across the stadium floor.
There will surely be a lot of flat wheels, though.
- Paul North.
Paul, nope, I didn't think our modern railroads would invest in a spped limit system that wouldn't know to turn off the motors when it applies the brakes. I'm thinking more that perhaps the locomotives are more powerful than a superman, and the sensors or time lag between when the system detects a speeding train and when the system takes action might be long enough that the locomotive could accelarate quite a bit before getting its brakes applied.
Existing signal systems, either wayside or cab signals, have discrete sensing sections, don't they? Is it possible that a train could pass a sensor below the speed limit, but accelarate fast enough after to cause problems before the next signal catches it?
I'm assuming Positive Train Control should not have such a limitation, that it uses some sort of radio or GPS gizmo to keep track in such short segments that it's as close to real time, and sensing the train in fractions of a second. If not, then I feel it's even more of a waste of money with little benefit.
I'd think that all a Speed Control needs to know is the speed limit on the section of track that the engine is on and the speed of the wheels. No need to rely on GPS to measure the speed between two places or some trackside sensor to tell the train how fast it is going. Granted, it might be traveling slower than the drive wheels indicate but surely there are undriven wheels that could measure the real speed of travel... it would also serve as a wheel slip sensor... If the drive wheels are going faster then the sensor wheel, then (figuratively) back-off on the gas pedal.
Semper Vaporo
Pkgs.
GPS provides near instantenous speed measurement without measuring between defined points. (I have a GPS transponder on the data aquisition system on my race car - it provided speed and other GPS dependent data for every foot the race car travels in and around the track) IF PTC has track speed and temporary slow orders added to the GPS data base for PTC operation - PTC knows how fast the allowed track speed is.
Never too old to have a happy childhood!
Unless you've got one of those new-fangled A1A-A1A Diesels, all axles are driven - there are no idlers.
It is very possible for one axle to slip to the point that it causes an overspeed. I've had it happen. The power is also cut, and there is a penalty brake application, at least on our RS18u's.
Even our vintage Diesels cut power when the brakes dump.
Modern locomotives have very sophisticated wheel slip sensors - all you'll note is a "tunk" as the wheel slips and power is reduced to that axle.
As for the base question, of course. It depends on the conditions and circumstances. Even a 600 HP SW1 might be too fast to be safe...
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
How fast is too fast is more a function of safe track speed than of locomotive capability.
One well-known class of locomotive was known for its ability to roll a moderately heavy train at a sustained 90mph without strain. One suffered a fatal rollover when it entered a curve too fast. The curve speed was posted at 15mph.
And now you know why N&W preserved 611. After repairs, she was the best J in the fleet.
As others have indicated, it's possible for modern electronics to prevent overspeed derailments - as long as they work, and can't be overridden.
Chuck
Not quite sure what system you are referring to. PTC will apply a penalty application when the train is about to exceed the maximum authorized speed. Don't understand why you think the train will somehow keep accelerating a significant time after that.
Even with PTC is will be possible for the engineer to apply both the brakes and the power at the same time.
Most railroads have engine overspeeds that aren't tied into the track at all. The engine max speed is set. Tied in cab signals are a set max speed based on signal indication, which is not the same as track speed. The engine doesn't know the speed of the track at all and the signal system doesn't know the speed of the train. That communication is what PTC is about and why they are spending billions of dollars to establish that communication.
That is very different than what happened in Phillie. The train was probably operating on a clear signal, max speed. The cab signal system doesn't know the speed of the track. So clear could be 150 on tangent or clear could be 50 in a curve. If the train passed a restrictive signal, the train would have to comply with the speed of the restrictive signal.
People highly overrate GPS. Engines may know where they are all the time, but that doesn't mean they communicate where they are to the outside world. For example some railroads only record where the engine is every 15 minutes and then upload it to the satelites once every 2 hours.
Dave H. Painted side goes up. My website : wnbranch.com
gardendance Paul, nope, I didn't think our modern railroads would invest in a spped limit system that wouldn't know to turn off the motors when it applies the brakes. I'm thinking more that perhaps the locomotives are more powerful than a superman, and the sensors or time lag between when the system detects a speeding train and when the system takes action might be long enough that the locomotive could accelarate quite a bit before getting its brakes applied. Existing signal systems, either wayside or cab signals, have discrete sensing sections, don't they? Is it possible that a train could pass a sensor below the speed limit, but accelarate fast enough after to cause problems before the next signal catches it? I'm assuming Positive Train Control should not have such a limitation, that it uses some sort of radio or GPS gizmo to keep track in such short segments that it's as close to real time, and sensing the train in fractions of a second. If not, then I feel it's even more of a waste of money with little benefit.
Cab signal systems that have speed enforcement equipment will have the PCS open for overspeed conditions. Cuts power and makes a penalty brake application. If you are below the overspeed setting for a certain signal indication and then go above the setting, the overspeed kicks in.
Jeff
Excuse me, "what happened in Philly." My understanding is that the old PRR cab-signal system with some speed restriction control, at least requiring acknowledgement if not a brake application, might have prevented the accident, but had been removed in preparation for the new system which was still to be installed and now is installed. Am I mistaken? The cab signals still worked, but the speed control had been deactivated and not yet replaced on the specific track.
Cab signals are for track occupancy and routing. They do not reflect temporary or permanent speed restrictions.
Train ahead. Restrictive signal.
Switch lined other than normal. Restrictive signal.
Track clear and switches lined normal. Clear signal.
dehusman Cab signals are for track occupancy and routing. They do not reflect temporary or permanent speed restrictions. Train ahead. Restrictive signal. Switch lined other than normal. Restrictive signal. Track clear and switches lined normal. Clear signal.
In your opinion. Jeff H seems to be saying something else, and he would know.
"Cab signal systems that have speed enforcement equipment will have the PCS open for overspeed conditions. Cuts power and makes a penalty brake application. If you are below the overspeed setting for a certain signal indication and then go above the setting, the overspeed kicks in."
C&NW, CA&E, MILW, CGW and IC fan
dehusmanThey do not reflect temporary or permanent speed restrictions.
Cab signals, as they exist today, and PTC are totally different.
Except when they do. If Amtrak wants a cab-signal restriction approaching a curve they can add it, as they did at Elizabeth 15-20? years ago.
Cab signal indications have very specific meanings and present a very limited range of options.
Displaying a signal for a condition that doesn't conform to the indication is really dangerous. If you display "approach" (which means to slow down to 30 mph and prepare to stop at the next signal) as a general "slow down" signal, then you dilute the meaning of the signal. That is hugely dangerous because it lulls crews into thinking that they got an approach because of a speed restriction when in reality they got an approach because the next signal is red.
Dave makes a valid point about signal aspects. Rapid transit systems will use a distinct aspect for speed control compared to an aspect related to track occupancy. As an example, CTA used yellow-over-lunar to control speed on the grades that led into the subways as opposed to yellow to indicate approach.
schlimm dehusman Cab signals are for track occupancy and routing. They do not reflect temporary or permanent speed restrictions. Train ahead. Restrictive signal. Switch lined other than normal. Restrictive signal. Track clear and switches lined normal. Clear signal. In your opinion. Jeff H seems to be saying something else, and he would know. "Cab signal systems that have speed enforcement equipment will have the PCS open for overspeed conditions. Cuts power and makes a penalty brake application. If you are below the overspeed setting for a certain signal indication and then go above the setting, the overspeed kicks in."
What Dave said is just as true as what I said. Most cab signal systems only respond to track occupancy. The speed control enforcement enforces the speed associated with the cab signal indication. Unless an artificial cab signal condition is induced for a speed restriction, the cab signal won't "see" it.
Not all cab signal systems have a speed enforcement component. Those that do are usually referred to as Automatic Train Control.
My experience in riding the front platform of LIRR and PRR MP-54's (first time at age 8, summer 1940, returning from the Worlds Fare, last time 1992, going to a job inspection at Princeton U.) is that the PRR cab-signal system DID, at least at one time, include speed control for permanent speed restrictions, or at least some permanent speed restrictions. The horn would blow, and the engineer would have to acknowledge.
You guys are giving me much edutainment and entercation about different kinds of signals, but not much info about if the locomotive can be so powerful that the system can't react quickly enough. Some of you have even suggested that I think the signal system would tell the locomotive to put on the brakes, but wouldn't be smart enough to tell it to turn off the acceleration, and this makes me sad. Won't someone turn my frown upside down?
You guys seem to know much more about all sorts of signal systems, but nobody's clearly answered what I apparently haven't phrased properly: can a train pass a place where the signal system checks its speed, going under the speed limit, and accelerate so quickly that it's dangerously over the speed limit before it gets to the next place where the system checks its speed?
Most of your replies mention what you think the signal system will do once it finds out the train's speeding, but don't mention how often the signal system checks speed, although dehusman mentions one system that RECORDS the speed every 15 minutes. If I remember correctly, Amtrak has an internet system that tells everyone train speed, but no mention of how often it checks speed, and apparently that system has nothing to do with controlling speed.
gardendance Can locomotives be so peppy that any overspeed controls would render them useless? This is kind of related to the Amtrak 188 wreck at Frankford Junction Philly. If I remember correctly the train didn't start speeding until near the end of 80mph territory going into 50mph territory and finished at over 100mph. It also seems to me that it traveled a relatively short distance to accelerate those 20 or so mph, when it should have decelerated about 30 or so mph. I've also read some posts that said although Frankford Junction curve's speed limit is 50mph that it's possible to traverse it at 80mph without derailing. Is the ACS64 so poweful that it could have accelerated from 50 to 80+mph so fast that an overspeed control would not have slowed it in time? Of course I may be way off on my numbers in this case, but in any case it seems to me that it's possible to have a locomotive whose accelration is so good, and some speed limits so restrictive, that no overspeed control would be worthwhile. Also of course there are some whose opinion is that Positive Train Control's cost-benefit ratio makes it not worthwhile either.
No. PTC is predictive, not reactive. It would enforce the braking curve needed to get the train down to speed in time for the curve. It wouldn't matter how powerful the locomotive is. It just has to know about train braking capability
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
BaltACD dehusman Cab signals are for track occupancy and routing. They do not reflect temporary or permanent speed restrictions. Train ahead. Restrictive signal. Switch lined other than normal. Restrictive signal. Track clear and switches lined normal. Clear signal. Cab signals, as they exist today, and PTC are totally different.
Cab Signal with speed enforcement gets close to some aspects of PTC, requiring braking (suppression style) or slowing (LSL) to adhere with speed associated with the signal aspect.
Suppression style required a 17# reduction when a more restrictive aspect was encountered and the current speed was over the speed for that aspect (e.g. you are running 60 mph on a clear and you get an approach medium (45mph) in the cab)
LSL required that you slow down to the speed associated with the next lower aspect's speed along a pre-programmed braking curve. (e.g. you are running 50 mph on a clear and get an approach medium. You have to slow down to 30 mph. You then get a restricting, you have to slow down to 20 mph.)
gardendance You guys are giving me much edutainment and entercation about different kinds of signals, but not much info about if the locomotive can be so powerful that the system can't react quickly enough. Some of you have even suggested that I think the signal system would tell the locomotive to put on the brakes, but wouldn't be smart enough to tell it to turn off the acceleration, and this makes me sad. Won't someone turn my frown upside down? You guys seem to know much more about all sorts of signal systems, but nobody's clearly answered what I apparently haven't phrased properly: can a train pass a place where the signal system checks its speed, going under the speed limit, and accelerate so quickly that it's dangerously over the speed limit before it gets to the next place where the system checks its speed? Most of your replies mention what you think the signal system will do once it finds out the train's speeding, but don't mention how often the signal system checks speed, although dehusman mentions one system that RECORDS the speed every 15 minutes. If I remember correctly, Amtrak has an internet system that tells everyone train speed, but no mention of how often it checks speed, and apparently that system has nothing to do with controlling speed.
Automatic Train Control is a continuous system. As soon as speed gets over the specific setting, it gives an audible warning for a few seconds (ours is 6 seconds) before taking the air.
In those few seconds you either have to get back under speed or go to suppression on the automatic brake.
Present-day systems determine the speed of the locomotive solely from on-board equipment (typically a mini-generator on one of the axle, or a speed sensor that is also part of the anti-slip / creep control feature, etc.).
Speed is not determined by wayside equipment such as radar, or a timer/ 'trap' setup that clocks how long the train takes to go a set measured distance, etc. The only examples of those that I know of are the ones that the Southern Rwy. used on the Saluda grade to determine whether the train was under control and going slow enough to continue down the grade, or was going too fast and needed to be switched into the safety track to get stopped before it went any farther.
gardendance .... can a train pass a place where the signal system checks its speed, going under the speed limit, and accelerate so quickly that it's dangerously over the speed limit before it gets to the next place where the system checks its speed?
.... can a train pass a place where the signal system checks its speed, going under the speed limit, and accelerate so quickly that it's dangerously over the speed limit before it gets to the next place where the system checks its speed?
No. But only because that's not how the systems work. The signal system doesn't check the speed. The signal system tells the train what the signal indication is. The engine reads the signal indication and then looks at how fast its going. If its too fast for the indication then the engine applies the brakes.
Most of your replies mention what you think the signal system will do once it finds out the train's speeding, but don't mention how often the signal system checks speed,
With any of the cab signal systems the speed control is based off the ENGINE. The external signal system doesn't measure the speed per se. Al the systems, including PTC feed the signal indications (or speed restrictions in the case of PTC) to the engine and the ENGINE determines whether the speed is being exceeded. Having the system external to the engine try and figure out the speed would be unsafe because of the possibility of communication failure.
If I remember correctly, Amtrak has an internet system that tells everyone train speed, but no mention of how often it checks speed, and apparently that system has nothing to do with controlling speed.
None of the external (to the engine) signal systems control the speed. They communicate the required speed tothe engine and the engine figures out whether its speeding.
Euclid Patrick, I don’t know how those systems work, but I understand your question. Basically, it seems to me that the external system would have to impose the speed limit for the track, and an internal system on the locomotive would have to continuously monitor speed and prevent it from exceeding the externally imposed limit.
With existing speed control (Cab signal based), braking curves are baked into the locomotive born device based on "worst case".
With PTC, the location along the track is a combo of GPS and dead reckoning. Which track is sent from dispatch system to train. Allowable track speed (civil limit) is in database on locomotive's PTC computer and is downloaded before the trip.
dehusman The engine reads the signal indication and then looks at how fast its going. If its too fast for the indication then the engine applies the brakes.
This, of course, is one of the major differences with PTC.
[quote user="gardendance"]You guys seem to know much more about all sorts of signal systems, but nobody's clearly answered what I apparently haven't phrased properly: can a train pass a place where the signal system checks its speed, going under the speed limit, and accelerate so quickly that it's dangerously over the speed limit before it gets to the next place where the system checks its speed?
I don't know whether you have been satisfied with the answers but it is my belief that the answer to your question is No. As has been stated, the signal system does not check the trains speed, it indicates the maximum allowed speed to the train. The train compares its speed and if that speed is exceeded, acts to get the speed reduced. The trains power is not a factor since the power can be reduced by the trains controls. However, in the Philadelphia accident, the signal system did not have track speed limitations in its capabilities so the signal system only was giving the train a clear signal that allowed it to go at whatever speed the engineer set. Thus the train was free to accelerate and therefore did not prevent the accident. PTC does include track speed information and could have prevented the accident.
As to whether the train could be powerful enough to overspeed, that is also a No because if the train has received the signal to not exceed XX mph, as soon as the train accelerated to that speed, the control system on the train would operate to reduce the speed.
And this assumes that there is, indeed, some form of cab signalling extant. Not all lines with signals have cab signals.
On lines without cab signalling (or any relative thereof), the speed of the train is controlled solely by the engineer. If he/she wants to blow by a "clear" signal at 80 in 40 MPH territory, well.....
The closest thing to external speed enforcement on such signalled lines and in dark territory (other than weed weasels) is a defect detector that reports speed, or a train report clear of a given point much sooner than they perhaps should have.
And we can't forget the event recorder, which tells all.
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