Railroad Forums 

  • Why signals? Why not GPS + radio network?

  • General discussion about railroad operations, related facilities, maps, and other resources.
General discussion about railroad operations, related facilities, maps, and other resources.

Moderator: Robert Paniagua

 #221068  by RussNelson
 
Why do railroads still use signals? Why don't they use a system where every train has a computer with GPS receiver and data radio networked back to the dispatcher and also to every other train?

We know how to make these systems reliable. They work for air traffic controll. They're planning to replace the radar-based air traffic control system with GPS+radios. If it's safe for airplanes, why wouldn't it be safe for trains?

 #221077  by DutchRailnut
 
reliable is not enough, a signal system needs to be fail safe.
how about loss of signal from satellite ?? how about interference ???
not even one nano second can it be compromized.

 #221086  by LCJ
 
Aircraft pilots can steer around obstacles in front of them. Engineers cannot. Unless a system goes to its most restrictive mode of operation upon failure, the worst can sometimes be unavoidable.

System are under development that utilize GPS technology to supplement the signal system to impose positive train separation. In my opinion, cab signals combined with automatic speed control and GPS interval protection should be a standard. This would, however, be very expensive to implement.

Railroads that have relatively inexpensive "dark" territory rely on the knowledge and compliance habits of operating employees without the basic protection of block signals tied into the track structure -- sometimes to the detriment of safety.

 #221116  by RussNelson
 
DutchRailnut wrote:reliable is not enough, a signal system needs to be fail safe.
how about loss of signal from satellite ?? how about interference ???
not even one nano second can it be compromized.
Yes, it needs to fail safe. Thus, every train and dispatcher knows where every other train is. If a train loses connectivity with the network, it will run according to a pre-determined schedule. Thus, every other train will know where that train MUST be.

Yes, there will be GPS satellite outages, but they will be predictable based on location. If the signal goes away when the train enters that location, nobody gets upset. The position estimation algorithm will assign an error value, and when a train gets too close to a silent train, it will stay far enough away for whatever safety margin you want. The real problem is not when one node goes off the air; it is when your entire network fails, and every train disappears, and you lose voice contact with the trains at the same time.

 #221119  by RussNelson
 
LCJ wrote:In my opinion, cab signals combined with automatic speed control and GPS interval protection should be a standard. This would, however, be very expensive to implement.
How expensive are signals? How expensive is human error? How expensive is a locomotive? How expensive is the downtime due to a wreck? Even if you don't give a crap about personell safety, these are all quanitifiable risks.

 #221128  by LCJ
 
I'm sorry to be dense here, but I guess I'm missing the point of your last barrage of questions. Or are they just rhetorical?

 #221137  by RussNelson
 
I mean to say that there is no such thing as "expensive" to a business. There is only "more expensive relative to something else" or "less expensive relative to soemthing else". It seems to me like GPS+radio is worth the money on a dark line. Knowing where your trains are beats guessing any day.

 #221149  by LCJ
 
Well, capital for such projects, in this imperfect world of publicly held entities, is available only to the extent that the revenues generated by operating trains on the lines in question justify the expenditure for the technology. There are always far more investment options than funds to invest -- unless you have a cost-plus government contract, that is.

Your idea is probably a good one. I don't know enough about it to judge. You should talk with the folks who supply advanced technology to railroads. You never know -- it may not have been considered as a possible solution.

 #221157  by CCCPR
 
RussNelson wrote:[quote

Yes, it needs to fail safe. Thus, every train and dispatcher knows where every other train is. If a train loses connectivity with the network, it will run according to a pre-determined schedule. Thus, every other train will know where that train MUST be.

Yes, there will be GPS satellite outages, but they will be predictable based on location. If the signal goes away when the train enters that location, nobody gets upset. The position estimation algorithm will assign an error value, and when a train gets too close to a silent train, it will stay far enough away for whatever safety margin you want. The real problem is not when one node goes off the air; it is when your entire network fails, and every train disappears, and you lose voice contact with the trains at the same time.

I mean to say that there is no such thing as "expensive" to a business. There is only "more expensive relative to something else" or "less expensive relative to soemthing else". It seems to me like GPS+radio is worth the money on a dark line. Knowing where your trains are beats guessing any day.
So what do you do when the train must be there, but it ain't there. You are planning on running a railroad like an airline. You are forgetting all trains don't move the same speed, they handle different, more prone to mechanical failure than aircraft. If two trains are following eachother and loose the GPS signal and moments later the first one hits the ditch or stops in emergency, the train following ain't gonna know about it. Radios can fail, the crews then loose communication between trains. You can have a computer or use mathematics to try to estimate where the train is gonna be, but if it doesn't have communication it ain't gonna know the train is stopped, doesn't sound failsafe to me. I'd still feel safer knowing that a signal is gonna keep me far enough away from running into the train ahead, I'd even feel safer in the outdated TWC/OCS(Canada) than have a computer try to predict where a train might be.

If GPS can fail and the radio can crap out, GPS+Radio does't seem fail safe at all.

 #221209  by DutchRailnut
 
What happens to a train loosing a satelite feed before crossing over to other track, will computer assume it continoud on same track it was ???

What happens if one train stops(planes don't) while satelite feed is lost.
The train behind it may have lost feed to and continous at its original speed.

Planes happen to fly above clouds and get controller fed radio and radar feeds backing up the GPS and planes own radar.
with trains that would not work.

 #221219  by JLJ061
 
GPS satellite feeds cannot tell the engineer the required speed he is to maintain; Signals can.

 #221227  by jg greenwood
 
JLJ061 wrote:GPS satellite feeds cannot tell the engineer the required speed he is to maintain; Signals can.
Not all railroads utilize speed signals.

 #221280  by LCJ
 
Every system devised for making railroad operations safer has been shown to have some cracks through which the occasional situation might fall. People, as imperfect and prone to disregarding prescribed procedures as they are, will find a way to get around any technology -- either accidentally or purposefully.

The ultimate safety of any mode of operation depends upon the attention and adherance of operators to prescribed procedures. Operation even in so-called dark territory is very safe if everyone knows what they should do in any given situation, and then actually do it.

And yes, managing railroad equipment traffic is a much different endeavor than that of aircraft. Falling back to a predetermined train schedule (a 19th Century solution), as a supposed fail safe, is ludicrous at best.

Is the use of GPS to supplement established track circuitry systems a good idea? I would say so. Is a GPS/radio system likely to supplant signal systems currently in use any time soon? I would say not bloody likely.

 #221286  by RussNelson
 
LCJ wrote:Every system devised for making railroad operations safer has been shown to have some cracks through which the occasional situation might fall. People, as imperfect and prone to disregarding prescribed procedures as they are, will find a way to get around any technology -- either accidentally or purposefully.
Yup. Signals can fail, operational policy can be ignored. I was mostly wondering if anybody has such a system, and if not, why not. Apparently nobody has.

 #221323  by GOLDEN-ARM
 
Just curious, Russ, you don't happen to sell, maintain or install the GPS type systems, in question, do you? As an aside, the airlines can fly, with GPS, but the amount of ATC's handling them, from ground, approaches, hand-off's, etc., you are talking perhaps dozens of people, to handle one flight. A single train can travel across a railroad system, with ABS rules in effect, without input from anyone. (in theory, the DS would have to set-up the CP's, or his operator would) As already mentioned, the sky is a big, three dimensional place. You can stack planes, fly them side by side, etc. Lot's of room up there, for mistakes, without consequenses. A single track mainline is no place for system errors, for untried technology. Sure, some mine railroad in Canada has used it, but the US rail system is not some smalltime mining operation, and this sure in the heck ain't Canada. Those GPS systems don't detect broken rails. Signals can, and do. They also know if a rail car is on the mainline, and will warn an approaching train. We already run trains, without signals. It's called "dark-territory", and it is no place to be, when the Stuff hits the fan. Wayside signals/cab signals in conjuntion with LSL is all that is needed in todays rail system. Price keeps it from becoming a reality, though. The technology is tried and true, and it DOES work, but railroads justify the continuing carnage, by blaming us for all that goes wrong, without stepping up to the plate, and implementing the technology that we already know works. I, for one, would be happier to never see GPS on board my train. The carriers already wish they "ride along" inside every train, every trip, watching our every move. This kind of thing certainly does not help, with regards to that. Save the GPS for the airlines, or tanks on the battlefield. You shouldn't try to re-invent the wheel, so to speak. Just my .02 cents, though. Regards :wink: