While GPS is a useful tool - the civilian version is still not precise enough to be the basis of a railroad signal system.
Civilian GPS cannot differentiate which of multiple tracks a train is on - a big issue when you have trains operating in opposing directions on the same segment of multiple tracks. Not only are their location of multiple tracks owned by a single carrier, there are locations where multiple adjacent tracks are owned by multiple carriers.
Never too old to have a happy childhood!
AnonymousWhat you are really talking about is Postive Train Control, which may use GPS as a component, or may not. It depends on the system. The capacity increasing aspect of PTC is it incorporates a system of "floating blocks," that is, the blocks travel with the trains rather than are permanently fixed to geographic locations. The short answer to your question is PTC might increase capacity, but at a cost that is very unattractive, so far. The electronic equipment is more expensive than traditional Centralized Traffic Control, which itself costs about $1 million per mile, because it requires equipping every locomotive and mobile track machine assigned to the PTC-equipped territory. The software is very complex and expensive -- think fly-by-wire systems on an aircraft. If a railroad doesn't equip its entire fleet with PTC, it takes upon itself a severe loss of flexibility in fleet management. The fundamental difference between GPS and railroad methods of operation is that GPS is an approximation (albeit a pretty good one) and railroad operation is yes/no. That is, a train is either approaching a control point, or it has passed a control point. All GPS does is tell you where a GPS transceiver is -- more or less -- which is not at all the same thing as a signaling system. If an aircraft is plus or minus 20 feet while flying, who cares? A train plus or minus 20 feet is on another track or beyond a control point. I've seen some bold claims of capacity increases with PTC, but there are many skeptics who disbelieve them. No one is rushing to buy it except people using other people's money (that is, taxpayers' money). We might see PTC experiments on high-density freight railroad routes within 10 years. You asked how much capacity could be increased: no one knows the answer to that question yet. Manufacturers claim 20-30%, but no empirical tests to validate those claims have been performed. And without a huge committment of cash on someone's part, a real-world installation (which would give you some real numbers) isn't going to happen.
Fly-by-wire and GPS in aircraft, are two separate things. The simple way to explain it is with the modern automobile. Most no longer have a mechanical linkage between the accelerator and engine. It's done with a computer. That computer has nothing to do with the GPS navigation system, if the car has one. Likewise, a fly-by-wire aircraft, means that a computer controls the aircraft's control inputs by the pilot. It does not perform navigation duties. That is the job of the flight management computer. Technically, you can have fly-by-wire and not have a flight management computer, and vice versa.
Much would be the same with a locomotive.
mudchickenMeter grade GPS is still insufficient for trains passing in sidings. This bug has been known since Rockwell's LARS, NTRAC & ANSAC days in the mid- 1980's.... To get things down to survey grade RTK GPS you need beaucoup base stations and a ton of software to sort stuff out on the fly. (Thus the expense...plus if the receiver loses "lock" under a bridge, tree or building you're had......then there is "multipath"...) The little Garmin handheld GPS units are anywhere from +/- 15 feet to hundreds of feet off in precision (Precision & accuracy are NOT the same thing....and accuracy is subjective)....when trains can pass each other with 1 or 2 feet two spare, the uncertainty is too much..... In time the computer processing and hardware costs will drop, in the meantime we'll just have to wait......Everybody is complaining about RCO's, this makes RCO's look like a minor bump in the road....... Travelin' Feathers ps.....(GPS & GIS are not the same either, far too many do not understand the difference.... Technology is a good thing - Failure to understand the technology creates unwanted expectations and/or blunders, as in brain failures that kill.....)
In 2004 you were correct. Today we have the wide area augmentation system, which provides much tighter GPS tolerences. Such is being implemented to replace traditional instrument landing systems in aviation. Those parameters are much more restrictive than would be required between a main and a passing track.
tree68I agree that GPS needs to be a component, not the whole shebang. Putting a GPS in both the FRED and the lead loco helps demonstrate train length. Adding some unit ID (such as the trucking industry now uses) with that helps the dispatcher keep track of who is where and how they are doing (all engines in notch 8, trainline normal, etc). On a straight section of track with no diversions, GPS with unit ID, together with some computer oversight (and a reasonable degree of confidence in the system), it would be possible to stuff quite a few trains in. Speed, weight, track profile, and the corresponding stopping distance could all be computed continuously, allowing train seperation to be minimal (factor in a cushion, there). Cab indications would replace lineside signals, and could give distance to next train, as well as a recommended speed. On the other hand, for close quarters (yards, passing sidings) where exact location is crucial, there's nothing like a track circuit. But, all that tech stuff costs money. It'll be a while. As an example of the application, though, the Phoenix, AZ, Fire Department has equipped all their apparatus with a system that includes GPS. They now dispatch by the equipment closest to the scene, as depicted on a map of the city that shows where all apparatus are.
This information is obviously very dated. Most limiting factors are now obsolete.
Paul_D_North_Jr 'Bumped' to make it active again, per my post a few minutes ago on the "It's quiet......too quiet. thread." - PDN.
'Bumped' to make it active again, per my post a few minutes ago on the "It's quiet......too quiet. thread."
- PDN.
Thanks to Chris / CopCarSS for my avatar.
Murphy Siding Paul_D_North_Jr 'Bumped' to make it active again, per my post a few minutes ago on the "It's quiet......too quiet. thread." - PDN. A note about "anonymous"- when someone leaves the forum, whether voluntarily or not, the user name changes to anonymous once the account is closed. There may be several different posters on this thread that have left. They all show up as anonymous. If you respond to a post bty anonymous, don't expect that person to reply.
A note about "anonymous"- when someone leaves the forum, whether voluntarily or not, the user name changes to anonymous once the account is closed. There may be several different posters on this thread that have left. They all show up as anonymous. If you respond to a post bty anonymous, don't expect that person to reply.
I've never seen that on any other internet forum.
Usually on other boards, the username is notated with "no longer a member", or their posts are removed.
BLS53 mudchicken Meter grade GPS is still insufficient for trains passing in sidings. This bug has been known since Rockwell's LARS, NTRAC & ANSAC days in the mid- 1980's.... To get things down to survey grade RTK GPS you need beaucoup base stations and a ton of software to sort stuff out on the fly. (Thus the expense...plus if the receiver loses "lock" under a bridge, tree or building you're had......then there is "multipath"...) The little Garmin handheld GPS units are anywhere from +/- 15 feet to hundreds of feet off in precision (Precision & accuracy are NOT the same thing....and accuracy is subjective)....when trains can pass each other with 1 or 2 feet two spare, the uncertainty is too much..... In time the computer processing and hardware costs will drop, in the meantime we'll just have to wait......Everybody is complaining about RCO's, this makes RCO's look like a minor bump in the road....... Travelin' Feathers ps.....(GPS & GIS are not the same either, far too many do not understand the difference.... Technology is a good thing - Failure to understand the technology creates unwanted expectations and/or blunders, as in brain failures that kill.....) In 2004 you were correct. Today we have the wide area augmentation system, which provides much tighter GPS tolerences. Such is being implemented to replace traditional instrument landing systems in aviation. Those parameters are much more restrictive than would be required between a main and a passing track.
mudchicken Meter grade GPS is still insufficient for trains passing in sidings. This bug has been known since Rockwell's LARS, NTRAC & ANSAC days in the mid- 1980's.... To get things down to survey grade RTK GPS you need beaucoup base stations and a ton of software to sort stuff out on the fly. (Thus the expense...plus if the receiver loses "lock" under a bridge, tree or building you're had......then there is "multipath"...) The little Garmin handheld GPS units are anywhere from +/- 15 feet to hundreds of feet off in precision (Precision & accuracy are NOT the same thing....and accuracy is subjective)....when trains can pass each other with 1 or 2 feet two spare, the uncertainty is too much..... In time the computer processing and hardware costs will drop, in the meantime we'll just have to wait......Everybody is complaining about RCO's, this makes RCO's look like a minor bump in the road....... Travelin' Feathers ps.....(GPS & GIS are not the same either, far too many do not understand the difference.... Technology is a good thing - Failure to understand the technology creates unwanted expectations and/or blunders, as in brain failures that kill.....)
Shortly before I retired at the end of 2016, CSX had affixed accelerometers to a number of locomotives to measures 'rough track' parameters and sent those measurments along with the GPS location where the measurements were taken.
A computer application in Jacksonville took the data that was reported by the locomotive and formulated a e-mail for the Track Supervisor of the territory to identify the measurments taken and the GPS identified location so the location could be manually inspected and any conditions found to be fixed. One statement was a part of the e-mail - GPS does not identify the track, if multiple tracks are at the location all tracks must be inspected.
I have no idea of the level of accuracy of the GPS that is being provided to Air Carriers or Rail Carriers - the levels of accuracy may be different.
BLS53 Murphy Siding Paul_D_North_Jr 'Bumped' to make it active again, per my post a few minutes ago on the "It's quiet......too quiet. thread." - PDN. A note about "anonymous"- when someone leaves the forum, whether voluntarily or not, the user name changes to anonymous once the account is closed. There may be several different posters on this thread that have left. They all show up as anonymous. If you respond to a post bty anonymous, don't expect that person to reply. I've never seen that on any other internet forum. Usually on other boards, the username is notated with "no longer a member", or their posts are removed.
BLS53This information is obviously very dated. Most limiting factors are now obsolete.
A lot has happened in those 14 years since that was posted.
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...
BLS53 mudchicken Meter grade GPS is still insufficient for trains passing in sidings. This bug has been known since Rockwell's LARS, NTRAC & ANSAC days in the mid- 1980's.... To get things down to survey grade RTK GPS you need beaucoup base stations and a ton of software to sort stuff out on the fly. (Thus the expense...plus if the receiver loses "lock" under a bridge, tree or building you're had......then there is "multipath"...) In 2004 you were correct. Today we have the wide area augmentation system, which provides much tighter GPS tolerences. Such is being implemented to replace traditional instrument landing systems in aviation. Those parameters are much more restrictive than would be required between a main and a passing track.
mudchicken Meter grade GPS is still insufficient for trains passing in sidings. This bug has been known since Rockwell's LARS, NTRAC & ANSAC days in the mid- 1980's.... To get things down to survey grade RTK GPS you need beaucoup base stations and a ton of software to sort stuff out on the fly. (Thus the expense...plus if the receiver loses "lock" under a bridge, tree or building you're had......then there is "multipath"...)
I'd be inclined to think MC's comments still stand.
In regards to ILS vs GPS+WAAS, it is relatively inexpensive to place a base station in close proximity to every airport that would need a GPS instrument approach. In addition, the reception issue (restricted view of satellites, multipath, etc) is nowhere near as bad for even the worst airports (e.g. Lindhberg Field) as it can be for even a typical RR line. I would also disagree tolerances for ILS, with the exception of altitue above ground (radar altimeter), a landing position off by minimum track spacing is not going to cause anywhere near the problems of "being on the wrong track".
A couple of things that could help substantially are low cost frequency/time references and phased array antennas. The first would help recapture of teh satellite signals after going under a bridge or through a tunnel. The latter would help to reduce problems with mutipath (and spoofing).
One thing to know about PTC and "which track you're on" is that PTC isn't going to use GPS to figure that out. That'll come from the field to the dispatching system to the train. The field knows when a train occupies a track and what route and is in place at an interlocking. That info comes back to the dispatching system where the train tracking applies a train ID to that occupancy.
GPS is only needed to tell the locomotive where it is along the track (relative to the movement authority)
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
That has not changed, most GPS being used by PTC is in atonomous mode. If you went Kinematic with HARN Stations broad casting position and you had monster processing capability on the locomotives, you'd still be dealing with a crapshoot on if it would work.
The general public and for that matter most engineers haven't a clue what it takes to get centimeter precision to work. All that new wayside signalling going in is included in what Balt is talking about. Most wouldn't understand the importance in scale factor with Grid to Ground either. Up here, some 6000 feet above the geoid, you could be 700-800 feet off. Datum?
BaltACDShortly before I retired at the end of 2016, CSX had affixed accelerometers to a number of locomotives to measures 'rough track' parameters and sent those measurments along with the GPS location where the measurements were taken.
Several railroads installed the same equipment, they all report wherever the engine is, they all report back to an AAR clearing center (Railinc??) and the data is sent to the various railroads for them to use.
Dave H. Painted side goes up. My website : wnbranch.com
Didn't realize that data was being routed through Ralinc.
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