traffic control

[dlund]

Hi,

I was wondering if there is a railroad system that corresponds to air-traffic control for aircraft. 

I don't really know anything about air-traffic control systems, so this question may be misguided, but I'm assuming that there is constant monitoring of the aircraft position and speed so the aircraft can adjust their speed and direction to avoid collisions and scheduling conflicts.

Is there something similar for railroads, where the speed and position is monitored and the trains adjust speed to avoid conflicts with other trains?  It seems like there has to be, but I don't know if that would work with railroads.

Thanks.

dlund 

 

[tree68]

Dispatchers keep track of where their trains are by a variety of methods.  In "dark" territory, it's by reports from the crews.  I'm no expert in signalled territory, but in some cases, the location of trains is indicated on the track plan displays.  Also in signalled territory, some railroads have their crews call out the MP and aspect of the signals on the radio, so the DS can track them that way, too.

As opposed to the airways, where each center has regional control of all airspace in their area regardless of airline, etc, railroads are controlled by their own RR dispatchers/centers.  CSX has a half dozen dispatch centers, virtually all of UP's dispatching is done from Omaha.  Thus it's possible for two trains on adjacent tracks belonging to different railroads to be controlled by two different dispatchers.

There are exceptions where two railroads intersect or otherwise directly interact.

[CShaveRR]

The rulebook of any railroad has entire chapters devoted to rules for keeping trains separated--be they ABS, CTC, DTC, or TWC for main lines, remote control zones in the yard, or even Rule 93 or 6.28 for anything that isn't a main track.  The responsibility lies with the operating crews to not be where they don't belong, but somebody like a dispatcher or yardmaster is running the show, with varying degrees of authority (he can throw the switches himself sometimes, or just write the permits and messages that keep the trains separate).

[TheS.P.caboose]

Sometimes the railroads also use track warrants (TWC) to move the traffic. They may use CTC (Centralized Traffic Control) as well.

[dlund]

Thanks for the responses.

"As opposed to the airways, where each center has regional control of all airspace in their area regardless of airline, etc, railroads are controlled by their own RR dispatchers/centers."

That's exactly what I was looking for.  I was specifically wondering how centralized the control is.  Based on what I've read, it seems like trains are more frequently delayed because of congestion.

I'm guessing that railroad traffic can't be controlled as precisely as air traffic.  Is that correct?

[Railway Man]

Thanks for the responses.

"As opposed to the airways, where each center has regional control of all airspace in their area regardless of airline, etc, railroads are controlled by their own RR dispatchers/centers."

That's exactly what I was looking for.  I was specifically wondering how centralized the control is.  Based on what I've read, it seems like trains are more frequently delayed because of congestion.

I'm guessing that railroad traffic can't be controlled as precisely as air traffic.  Is that correct?

Neither one is a precision system from the perspective of the control center.  Neither needs to be.  All that matters is that the airplanes or trains don't collide with each other, and that both systems have a reasonable idea where the vehicles are and where they're going for planning purposes, so both systems are designed to place space between the vehicles with sufficient buffer so that precision control isn't needed.

Comparing the two modes of transportation is not very meaningful because one can move in three dimensions and the other in only one dimension; one can stop and stand still safely (and that is often the safest course) whereas the other if that is tried plummets to the earth; one has multiple companies operating using a standardized system owned by the government whereas the other is a single company using a system not quite standard among companies and owned by the individual company; one has a system that 98% resets every night at roughly midnight and starts over the next morning whereas the other runs 24/7/365 and never resets; one is very much at the whim of weather whereas the other not so much; one is at the mercy of geography whereas the other not so much; and so on.

One thing the two modes do have in common is the causes of congestion.  In both cases it's too many vehicles trying to occupy too little space at the same time.  And in both cases the congestion occurs mostly at terminals.  Airline delays are virtually 100% caused by too many airlines trying to operate too many flights arriving and departing an airport than the airport has capacity in a given time period -- the lanes between airports usually have plenty of spare capacity.  Railroad delays are roughly 75% a terminal issue, the other 25% the line capacity between terminals.  Railroads have a lot more control over their congestion issues because they own the track; if they're congested it's because they choose to be.

Neither railroad dispatching centers nor airline traffic control centers know precisely where the train or airplane is, and at least in the case of railroads they would have no use for the information (I don't know what use it would be to an airline control center either).  Railroad dispatching systems provide for sole occupancy of a track between specific geographic limits for each train.  Signaling systems are on overlay on this system that provides indications to a train crew to tell it when it can proceed, and at what speed, and when it should begin braking to a stop, and the point at which it must not pass.  It's very safe in practice and while the details are complex the theory is simple. 

The latest development in train control systems is to use precision locating instrumentation consisting of combinations of GPS, axle counters, and transponders affixed to the track structure so that trains can precisely location themselves in relation to a premapped track database in their train-control computer, and thus make use of predictive braking curves to ensure positive decelerations and stops to prevent trains from exceeding permanent or temporary speed limits, and from exceeding their authorized territory (and entering another train's territory and possibly colliding).  In this system the trains "talk" electronically to each other, not to the control center per se, only advising the control center of status on a low frequency of reports (maybe once every 5-15 seconds).  Each train's computer knows the limits of the train, and should it somehow manage to approach its limits at a speed beyond which the computer thinks the train can stop, then it informs the train that's in the limits about to be entered without authorization so that the other train can brake if it's approaching the same location.

As far as I know aircraft use similar locating systems also for collision avoidance.  In both cases the control center doesn't have to know a thing about the precise location of the train or airplane, and in fact trying to keep the control center updated in real time uses up so much processor power and bandwidth that when it's been tried (at least for railroads) the system didn't function.  All the railroad control center needs to know is approximate location for dispatching purposes.  An analogy is sending your kid to school: you want to know that he's attending class, but whether he sits down 1 minute ahead of the bell or right at the bell is not really that important.  While it might seem like a nice-to-know, it's an expensive proposition.  When it comes to system design and integration, the more information that can be deleted from analysis the better off the system is.

RWM

[dlund]

Thanks for the detailed response!

 

 

[Alan Robinson]

There's another complication. In the air traffic control world, the vast majority of air traffic is not under the control of any centralized system at all. I'm referring to light, non-commercial aircraft flying under visual flight rules. This is essentially a see and be seen world. Yes, each aircraft these days carries a transponder to help it show up on air traffic control radar, but in uncontrolled airspace and at uncontrolled airports, there isn't even a requirement to have a working radio on board some aircraft.

In the early days of the rail network in the United States, the first vision was that a company would build the tracks (or railway) and then charge the public, meaning whoever wanted to use the tracks with his own carriage equipped with flanged wheels, to have at it. Clearly, this system soon fell by the wayside. It shows how far we have come in developing means to operate railroads efficiently.

[Flint Hills Tex]

In Canada, dispatchers are called Rail Traffic Controllers, and are government employees, just the same as Air Traffic Controllers. IIRC, all RRs operating in Canada use uniform operating rules and signal aspects, which I personally find much more efficient and progressive than the US system(s).

It's fun listening to the dispatcher/train crew communications via rail-scanner or online:

www.railroadradio.net

And the following link gives you an insider's look at dispatching:

www.haleytower.org/laments/index.html

 

[Railway Man]

In Canada, dispatchers are called Rail Traffic Controllers, and are government employees, just the same as Air Traffic Controllers. IIRC, all RRs operating in Canada use uniform operating rules and signal aspects, which I personally find much more efficient and progressive than the US system(s).

RTCs that dispatch CPR and CN are employees of CPR and CN.

https://cpr.tms.hrdepartment.com/cgi-bin/a/highlightjob.cgi?jobid=1626&lcid=en-US

There have only been two major railroads in Canada since the early 1900s, before signalization was well-established, so it was much less complicated to institute common signal aspects. 

RWM

[FTGT725]

Along the same lines, can someone give me a definition of a Control Point (CP)?

[Dutchrailnut]

A CP  is a signal or interlocking controled by dispatcher at operations control center.

 

[Railway Man]

Along the same lines, can someone give me a definition of a Control Point (CP)?

From the Operating Department perspective, a CP is a location designated in the timetable that trains shall not enter or pass without authorization from a train dispatcher or control operator.  Control Points are often used in dark (unsignaled) territory.

From the Signal Department perspective, the CP is the trackage between insulated joints on which entrance is governed by absolute signals, and priority and direction of train movement is controlled by a train dispatcher or a control operator.  A CP can also be a location without space between the insulated joints equipped with opposing absolute signals, e.g., a hold signal.  An automatic interlocking is not controlled, but they're often called CPs anyway.

RWM

 

[chad thomas]

Controll points are typically the signals that controll the mergeing / diverging route locations (like the ends of a sideing). While the signals between sideings are intermediate. Intermediate signals are not dispatcher controlled, rather controlled by the track occupancy conditions of the following blocks.

[dehusman]

From the Operating Department perspective, a CP is a location designated in the timetable that trains shall not enter or pass without authorization from a train dispatcher or control operator.  Control Points are often used in dark (unsignaled) territory.

From the General Code of Operating rules(GCOR) (used by virtually every US railroad west of the Mississippi) a control point is defined as "the location of absolute signals controlled by a control operator."  So by default it wouldn't be in dark territory (at least not in GCOR territory).

Dave H.

[dehusman]

In the early days of the rail network in the United States, the first vision was that a company would build the tracks (or railway) and then charge the public, meaning whoever wanted to use the tracks with his own carriage equipped with flanged wheels, to have at it. Clearly, this system soon fell by the wayside.

That's an interesting take.  I have never read that intent.  All the US railroads I have ever studied were intended as private concerns all the way back into the 1830's.

Dave H.

[dehusman]

Dispatchers keep track of where their trains are by a variety of methods.  In "dark" territory, it's by reports from the crews. 

In DTC and TWC (dark or signalled) its where the dispatcher has given crews authority. The crews have to call into the dispatcher to get more authority, blocks (DTC) or warrants(TWC) in order to proceed.

I'm no expert in signalled territory, but in some cases, the location of trains is indicated on the track plan displays.  Also in signalled territory, some railroads have their crews call out the MP and aspect of the signals on the radio, so the DS can track them that way, too.

In ABS/DTC or ABS/TWC the position of the train is only generally known, most systems indicate the area over which the authority has been issued but only an approximate location of the train. In CTC the displays indicate which block (section of track) the train is in.  Some blocks are between absolute signals and some systems break those blocks down into smaller sections (2-5 miles long).

The calling out of signals is for the benefit of other trains.  While the dispatcher might hear that  typically a dispatcher wouldn't be paying attention to that because he might have 40 trains and 50 radio towers on his territory is only listening to one or two at a time.

As opposed to the airways, where each center has regional control of all airspace in their area regardless of airline, etc, railroads are controlled by their own RR dispatchers/centers.  CSX has a half dozen dispatch centers, virtually all of UP's dispatching is done from Omaha.  Thus it's possible for two trains on adjacent tracks belonging to different railroads to be controlled by two different dispatchers.

You might have two railroads that run adjacent to each other, each controlled independently, but if you have two main tracks it would be EXTREMELY unusual to have different dispatchers on different main tracks.  Normally one dispatcher handles a route, regardless of how many tracks it has.  And regardless of who owns the trains, it is under the control of the dispatcher that controls the track.

Dave H.

[tree68]

I knew someone would flesh out what I wrote more accurately. 

I've heard the DS call crews many times in the nearby dark territory to find out where they are.  Usually it's so the DS can get back the track behind them for a following train.

No question on the calling the signals thing - but a DS can use that method if he or she wants to.  Of course, not sitting in the dispatch center, I don't know if they do, or even want to...

The adjacent track thing assumes that two different railroads own the tracks, as opposed to two main tracks operated by the same railroad.   I think I recall a picture of the 20th Century and the Broadway running side by side coming out of Chicago.  I'd bet each was on its own authority from its own dispatcher. 

[Anonymous]

FYI have you ever seen Train Dispatcher? The current version is 3. It is a Railroad simulation of CTC type dispatcher screens.

Rgds IGN