But the pure communications based systems will not detect a broken rail.
Possibly a practical eventual system would use both communications and track-wave-guide technologies to provide both redudancy and no reduction of safety from track-circuit fixed-block tedhnology.
The rolling blocks I've read about for freight railroads have all been on communication based detection of trains, mow equipment, switches, etc. Each piece reports it's location and/or status. No signal sent out through the rails. Although I recall hearing that (I think) Rockwell-Collins was working on a collision avoidance system along those lines years ago. I think they did some testing on the CRANDIC, since the person who told me this worked for them.
Jeff
I should have said "conventional track circuit," and was wrong to leave out the word conventional. These are of two types. One is the normal dc or ac, with insulated joints between block. Either a short, from occupancy, or open, broken rail, means a stop indication, and approach at the preceding block. A more sophisticated block track circuit system does not have insulated joints, but a resonant specific frequency shunt between rails at the demarkation between blocks, and the track circuit is tuned to measure changes in the reactive and resistive impedences between shunts, with changes either way causing the stop signal. These are both what I would call conventional.
A moving block system sends signals from the train down both rails with respect to ground. Occupancy, or anything abnormal, will send back a reflected signal, with or course a break in the rail a very different signal than occupancy. Also, the reflected signal from both are compared.
Jeff: Didn't the old Galena Division of the CNW get along fine without lineside signals for years, at least until the UP installed their style signals within the past ~5 years.
C&NW, CA&E, MILW, CGW and IC fan
Without a track circuit, I would like to know how the broken rail is detected. Besides the possible derailment, that is.
Checking my source, you are right about MN and NYCTA. On both, fixed blocks remain. Possibly going to "rolling blocks" in the future. But properly designed, rolling blocks without track circuits can not only detect broken rails, but sun-kinks as well, something trackcircuits have not yet been developed to do!
Metro North has removed wayside signals from most of its third-rail-operated lines, except at interlockiings. The L line has removed them between 8th Avenue and Eastern-Parkway-Broadway-Junction-East-New-York. Between there and Canarsie, both ATO and the wayside signals with the old trip hamers remain operstional. I can understand this, because in the old days there was a Broadway Elevated - Williamsberg Bridge local Chambers Street - Atlantic Avenue service with alternate trains exdtended to Canarsie; these remained from the days before the completion of the 14th Street Canarsie line. The J, M,and Z routs are not ATO, and at times trains from these routs may require diversion to Canarsie. West (RR south!) of EP-BJ-ENY diversions from other routes would require back-up moves and are not likely, so only ATO-equipped trains operate, the L line.
My source says there may be one signalled North American light rail line that does use moving blocks and suggested I check on it.
blue streak 1 mudchicken , I'm happy with a little more redundancy to help process what's going on around me. As a pilot must agree. Cannot list the number of times when one of the following ADF, consulan, VOR, Loran, OMEGA, INS, IRS, GPS, ILS failed to provide proper info but some of the others came to the rescue and make a trip a non event. IMO too many system developers try to put all your eggs in one basket.
mudchicken , I'm happy with a little more redundancy to help process what's going on around me.
, I'm happy with a little more redundancy to help process what's going on around me.
As a pilot must agree. Cannot list the number of times when one of the following ADF, consulan, VOR, Loran, OMEGA, INS, IRS, GPS, ILS failed to provide proper info but some of the others came to the rescue and make a trip a non event.
IMO too many system developers try to put all your eggs in one basket.
and overlook the hole they designed in the basket!
Never too old to have a happy childhood!
daveklepper I will check on your statement about nobody having rolling blocks. I was told in 1996 that is was in the works and assumed it had been implemented by now. But I was also told it wouldl handle objects on the track and broken rails, since the rails are the carriers of the sensing high-frequency signals.
I will check on your statement about nobody having rolling blocks. I was told in 1996 that is was in the works and assumed it had been implemented by now.
But I was also told it wouldl handle objects on the track and broken rails, since the rails are the carriers of the sensing high-frequency signals.
Dave: read the article in Railway Age posted by BALT concerning how fixed blocks and wayside signals got retained unnecessarily by the rail operating departments in PTC adoption.
Change is a process, never instant and never goes the way we expect it.
That being said, the trackmen's poor experience with TAWS and ARES what it was, I'm happy with a little more redundancy to help process what's going on around me.
In the works and in place are vastly different things. MN, like many other commuter railroads is having trouble getting fixed block PTC in place much less getting something up and running that no one else has on a mixed use railway.
jeffhergert Some bridges also have fire protection circuits tied into the signal system. Jeff
Some bridges also have fire protection circuits tied into the signal system.
Don't overlook Slide Detector Fences.
I believe that the protection afforded by slide fence circuits is just as much a part of the system as that afforded by the broken rail detection.
Johnny
I don't believe any one has "rolling blocks" yet. That is one of the things on the wishlist for eventual versions of PTC and the like.
Just because there are no lineside signals does not mean there are no blocks and the associated track circuitry. On the exCNW ATC lines where there was no wayside signals, there were still block boundries. They weren't marked but eventually you knew where they were. (The UP added a directional block system using only cab signals on a line or two in northeastern Kansas. From what I understand, they placed signs at the block boundries. The signs read something like, "Cab Signal Aspect Change Location." The signs may not be maintained anymore. They were needed when we were required to run a train length after the cab signal cleared up at other than a signal or known aspect change location. Like Zug, we can comply immediately when the cabs clear up.)
Block systems also provide broken rail protection. Some have invisioned going to a completely communication based control system that does away entirely with blocks and signals. Because of the broken rail protection, there will likely always be some form of signal circuitry. It may be removed from actual traffic control (except when a break in the circuit happens) and the blocks may be longer than conventional signal blocks, but I'd bet there will always be a track circuit on busy lines.
When you eliminate block signals and track circuits and use audio or radio-frequency distance sensing for movable blocks, you can increase the capacity of a constant-speed double-track railroad by 50%. That is one reason why Metro North has moved in that direction. The subway system is doing the same with but with the addition of automatic operation, now the L 14th Street Canarsie Line, soon the 7 Flushing Line, and then the common Bronx portion of the 2 and 5 for the first use of trains that run on conventional block signals with the old trip-hammer safety device and the movable block with automatic operation system. Redudancy is built into both the Metro-North and Subway systems, and the two channels in use have to agree for operation to continue. And manual override at restricted speed is, of course, possible. The subway does not use cab signals in addition, but I believe Metro North does, or has an indicator that provides the same information. The whole shebang requries less maintenance than wayside sighals.I believe Bay Area and Washington Metro do not or did not have the redundancy in their automatic operation that New York has.
Playing the devil's advocate...
When I'm sitting in Deshler, waiting for the next train to pass, I'm watching ATCS, not the signals. Sometimes we'll check the signals to see if they confirm what we're seeing on the screen...
There's no doubt that lineside signals are valuable tools, but I do feel that technology will render them obsolete in most cases.
Recall that a device has already been developed that will warn motorists of the presence of an emergency vehicle in the area.
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...
UM......
(1) More than just the folks in the cab of a locomotive depend on lineside signals.
(2) The big organic processor behind the eyes and between the ears is the biggest safety device out there. Trading that in and running solely on electronics will just create another WMATA tragedy.
As technology advances (not to mention PTC), I would opine that even cab signals that get their information from the rails will go the way of the dodo.
The only reason to have track circuits will be to indicate that something is shunting (shorting) the rails or that there is an open (broken rail). Eventually, I'd bet that every car will have a GPS/transponder.
We aren't really that far from there now.
All seems so strange to hear all these different operating styles. In Canada in CTC it's all about the block signals. VIA is allowed to do 100mph in the standard CTC.
I don't know why anyone would want the railroads to take down the block signals. Not only do they give information about what's ahead they split up sections of track. It would be tough to not have that marked.
Cab signals would be great for foggy and around a blind curve situations but we get along fine without it.
10000 feet and no dynamics? Today is going to be a good day ...
It HAS happened on Metro North. In 1996, while I was still commuting between GCT and WPlains North Sta., the only wayside signal still left in operation from Mott Haven to White Plains North Station were approach and home signals for interlockings. I believe this has been expanded since to the entire electrified terratory, both Hudson and Harlem, north of Mott Haven, and possibly also the four tracks into GCT. Not sure about the New Haven or other diesel territory. I think floating-block technology may have been applied at the same time, but I a unsure about this.
I speculate that the complete replacement of wayside signals with cab signals is inevitable. It just hasn't happened yet.
mudchickenWhen you're preoccupied with watching a screen instead of looking out the wndow/ windshield. I-Zombies gone railroading.
Not really. We have territory that is cab signals without waysides. Works fine. Cab signal tree is between teh windshields (or above it). A quick glance out the corner of your eye and you know what you are running under. If the aspect goes more restricting, you have to acknowledge it. (and you quickly learn the cut sections).
A lot safer than relying on waysides only, IMO.
Plus it's a lot more efficient. Wihtout cab signals you have to run long blocks under approaches (or restrictings) until you find your next signal. Under cabs, as soon as the track opens up, the cab signals go up, and off you go. It's awesomeness.
The opinions expressed here represent my own and not those of my employer, any other railroad, company, or person.
Aren't lineside signal defined as the back-up to PTC?
What do you do if the cab signals fail? Without cab signals (under our rules) you can run on wayside indications, not exceeding 40 mph without an absolute block. Once you receive an absolute block, you can run up to 79mph on wayside indications. Without wayside indications and without an absolute block, you can run at Restricted Speed.
With wayside signals, it's easier to authorize an absolute block. You can't pass a Stop, Restricted Proceed, Restricting (except to clear the main track at a switch immediately past the signal) without permission. With waysides then the Block can be established with trains ahead within the abolute block limits. Routinely when giving us an abolute block the dispatchers give it for the entire crew's run. Without waysides, there can't be any train ahead within the absolute block limits. The blocks granted were shorter or sometimes they couldn't give one at all and you had to run at restricted speed. I remember a few times due to heavy traffic where we ran 15 or 20 miles at restricted speed.
Waysides also allow non-equipped engines to operate, where allowed by timetable/special instructions, to operate between certain points. For example, trains between Council Bluffs and Sioux City don't need to have an ATC equipped engine to operate between CB and Missouri Valley, Iowa. They can run 40 mph on wayside signals. (I've read that PTC ws also to have such a provision to allow a railroad that doesn't otherwise need PTC, such as a short line, to operate up to 20 miles over a PTC equipped line.)
Without the wayside signals, you still have to maintain all the circuitry for the blocks. Then you have to have the extra gear that transmits the signal code pulses through the rails. You have to maintain the receiving gear on the locomotives. No matter which route is taken, keeping trains apart on a busy main track isn't going to be cheap.
caldreamer Having developed the requirements, analyzed systems and written more programs than I wish to count, I can tell you that the more complex the system the more prone it is to errors. No matter how much testing you do on the software, you cannot think of every situation that PTC will encounter and program it into the system. In addition their is an old trueism in the computer world "GARBAGE IN, GARBAGE OUT". In other words bad data will result in bad results.
Having developed the requirements, analyzed systems and written more programs than I wish to count, I can tell you that the more complex the system the more prone it is to errors. No matter how much testing you do on the software, you cannot think of every situation that PTC will encounter and program it into the system. In addition their is an old trueism in the computer world "GARBAGE IN, GARBAGE OUT". In other words bad data will result in bad results.
Apparently lineside signalling falls short... hence the push for PTC. Signals (lineside or otherwise) don't matter if no one is watching them.
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