For 40+ years concrete slab track has been used in tunnels, for example to gain extra height for overhead wires when existing lines are electrified. It is also used extensively on light rail projects. Ballastless track has a low regular maintenance requirement compared to conventional track, especially for high-speed lines and tracks subject to fouling by drifting sand.
Ballastless track is expensive to install. Many designs require a top-down method of construction in which the rails are held in the correct position while concrete is poured underneath to form a slab. If a cheaper form of ballastless track were to become available it might become a serious competitor to conventional track.
The two links below might be of interest:
http://www.railengineer.uk/2014/06/24/asfordby-tunnel-trials/
https://www.railengineer.uk/2014/04/22/sand-ballast-dont/
The IVES system in the first link and the Tubular Modular Track in the second *might* become competitors to conventional track for new lines and for multi-tracking existing routes. In both cases, an asphalt base can be laid with adapted highway machinery and the prefabricated concrete slab/tie (IVES) or longitudinal concrete bearers (TMT) laid on top. Using asphalt and prefabricated concrete components should speed up construction rates (compared to using wet concrete).
A sub-roadbed will still be required. It's not going to be like putting together snap-track on your dining table.
In the end, it will come down to dollars and cents. If the cost is less than conventional track over some period of time, it will gain acceptance.
The replaceability will also be a factor. With a few gons worth of ties, some track, and some associated hardware, a line laid with wooden (or concrete) ties can be back in service in literally hours, given the appropriate machines, etc.
Having to dig out and demolish a section of this stuff would probably put a line out of service for days.
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...
Since I have been interested in this area since the early '70s (before getting out of high school) I'll jump in.
IslandManMany designs require a top-down method of construction in which the rails are held in the correct position while concrete is poured underneath to form a slab.
Both IVES and PORR are inherently top-down systems - but is there something supposed to be wrong with that? The Amtrak testing of Class 9 track was a bit more intensively top-down (geometry being much more critical for very high speed) and for a system intended to have zero or low maintenance in line and surface for many years, getting the geometry correct at the actual railheads and adjusting the support accordingly seems like highly sensible methodology.
I participated in one of the early 'asphalt in railroad construction' competitions in late 1975 or 1976, in which continuous paving of properly-subgraded ROWs figured largely as a design alternative -- the problem being that whether or not you think 'dowel pins' and heavy weight will keep the track laterally aligned, once you get a good hot day that asphalt layer can bite you. (I believe there were sections of the Transcon that were built using asphalt in the subgrade, as a sealing layer not dissimilar to its function in 'tarmac' roads, and when these got up to liquidus they sun-kinked like nobody's business...) This led me to discard asphalt comparatively early and look at some combination of RCC, concrete and tremie as a better solution to more 'permanent' alignment.
There was a sort of renaissance of investigation into actively sprung/suspended track at around that time, looking back into the German experiments just after WW1, and I thought at the time that very-high-speed track would require some form of suspension to be capable of absorbing all the reflected energy without permanent distortions or excessive resonance reflection back into the vehicles. This used a slip-cast or sectional trough, with appropriate reinforcement, post-tensioning tendons, etc. (with the ability to mud-jack the sections if needed to overcome earth changes) and continuous beams with elastomer and clamps for each rail and adequately robust gauge holding. The 'suspension' allowed at least some of the differential expansion in welded rail to be accommodated; lateral thrust was handled with elastomer between the running beams and hardpoints cast in the troughs. The beams were to be top-down aligned, and the suspension contact/support points were to be tremie'd in a manner similar to the PORR sections (although with much less volume of pumped concrete!) and only these comparatively few points would have to be adjusted to keep the track beams in correct line and surface if the trough settled or twisted.
I have liked the idea of the Tubular Track for many years, since I first saw it demonstrated in South Africa. It has an advantage in that trespassing anywhere near the rail, or crossing the lines, is extremely difficult! A potential problem with it, though, is that the gauge beams seem susceptible to damage from derailments or some kinds of dragging equipment, and I think it is particularly important to recognize all the potential drainage issues; perhaps more appropriate for North American use, the grade-crossing issues can be severe (compare the problems with road regrading in Biloxi, for example). I'm a bit surprised that some of the projects now being built with NTC machines haven't used this construction, particularly for projects that will have high-level platforms.
tree68A sub-roadbed will still be required. It's not going to be like putting together snap-track on your dining table.
Part of the premise is that all the necessary subgrading can be done continuously without 'finish precision', ultimately using good HA differential GPS to do finish grade directly with the field machines. MC has commented on this before, and I hope will do it again here...
Another part of the premise is that automated tracklaying has now become a reasonable specialty, with companies able to supply both equipment and know-how in the way Rcrane can for bridges. But much of the equipment is just as 'happy' working with panelized stick track as it is with slab or fixed track systems, and as tree68 noted much automated track machinery works well at periodic line, surface, and maintenance in ways that might be more cost-effective overall than the equivalent for fixed systems that suffer subgrade problems, environmental damage, etc.
You seldom see the slab=track proponents discuss this; they like to concentrate on that 40 to 60 year 'life' without mentioning that there are things other than normal wear and tear that can damage track and grade structure...
Weak, marginal, or too-variable subgrade bearing capacity - including expansive soils, and the heavy loads, high impact, and vibrations caused by US railroad equipment at speed, are severe challenges to any of these systems.
Concrete ties - a good idea with some valid benefits - have demonstrated the sometimes-truism that "Every advantage has a disadvantage". A lot of money and faith was put into them, only to find out some years later that abrasion under the rail seat was causing wide gage and stability problems - and this weakness is ongoing. Not enough to completely negate their added value, but definitely a tarnish on it.
- PDN.
Agree with PDN 200%
Might not be a big deal laying down slab track, but trying to get the S/G to near perfect grade and surface is going to eat your shorts.
With concrete ties, the subgrade had better be solid or you dig up half of your R/W in CO and NM like BN did in the 80's & 90's . (DC & I can remember the ATSF headache/disaster at and along the El Dorado KS line change, including a section of PacTrac/Slab track when the subgrade liquified under tonnage and multiple attempts at fly ash stabilization.)
OP bought the hype - hook, line & sinker. Slab track has a place (usually over relatively short distances), but it's hardly a universal option. IM might want to look at the documented fails in the AREMA proceedings, at the AAR/TTC test track fails & successes and ask himself how he is going to adjust that slab track after Ma Nature* decides to not play by the designer's rules and tonnage physics comes into play.
(*) Railroaders M/W Rule #1 - Mother Nature Is A B__tch!
mudchicken(*) Railroaders M/W Rule #1 - Mother Nature Is A B__tch!
In accordance with M/W Rule #1 is Rule #2 - all ground is not the same.
Never too old to have a happy childhood!
Asphalt under conventional ballast has been in use for many years. The following link gives the results of tests performed on asphalt sub-bases of various ages:
http://www.engr.uky.edu/~jrose/papers/Hot%20Mix%20Asphalt%20Railway%20Trackbeds.pdf
It perhaps depends on how near the surface the asphalt layer is. On a highway the asphalt is inherently exposed to the sun and is the perfect color for absorbing solar radiation! Under a couple of feet of crushed rock, or one-ton slabs of concrete, the asphalt will be protected from the sun, from UV and from extremes of temperature. Temperature change will also be more gradual.
It may be easier to adjust an asphalt-based system than one based on OPC. Some forms of concrete do reach maximum strength quite quickly, e.g. concrete based on calcium sulfoaluminate cement.
Top-down construction gives excellent results though like most ballastless track design it is aimed at producing very high quality track for high-speed lines. For freight lines with a design speed of <100 mph something simpler to build and cheaper might be better (Tubular Track seems about right).
If ballastless track starts to become more common it will be used for new construction, multi-tracking of existing routes and really deep reconstruction of existing lines, i.e. the sort of situation in which CWR with concrete ties is used at present. Short lines and regionals would probably stick to conventional track with spot replacement of ties, use of relay rail and ballast cleaning and tamping.
mudchickenRailroaders M/W Rule #1 - Mother Nature Is A B__tch!
MC,
Based on what I learned from my (now retired) track foreman friend you are spot on. The Spring thaw was the worst in his opinion. Thaw/freeze/repeat wreaked havoc on the track. My having an interest in MOW and following his crew resulted in my gleaning a bit of knowledge. I still have far to go to catch up to what that man knew by heart. He hired on at age 18 and retired at 60. Took a lot of knowledge with him when he left. Waiting to see how the new track foreman performs, and so far the crossing repairs are not a good indication of his performance.
I'm sitting by waiting for indications of improvements. Signal maintainer friends say those improvements may be in the offing.
Norm
Waiting for Island Man to start singing the praises of PTC. ...Broad brush, "pie in the sky" approach is a very dangerous approach in this industry.
Jerry Rose will tell you about the fails along with the successes. (he's an AREMA fixture, especially with one of my committees.)...
Going back to the concrete tie analogy, you ought to see what happens with unconfined slab track in tension
Slab track is most commonly seen in at-grade road crossings and the results there are mixed. (Indiana DOT is in lust with it)...the fails aren't pretty and as stated above the subgrade is usually the culprit. Trying to add things like asphalt subgrades and geomats only drives up the cost$ and lengthen$ the proce$$.
BaltACD mudchicken (*) Railroaders M/W Rule #1 - Mother Nature Is A B__tch! In accordance with M/W Rule #1 is Rule #2 - all ground is not the same.
mudchicken (*) Railroaders M/W Rule #1 - Mother Nature Is A B__tch!
mudchickenDRAINAGE-DRAINAGE-DRAINAGE
I thought that was Trump's line.
How well does the 'slab track' ballastless model hold welded rail in place as Moms Nature plays ambient temberaturs like a slide trombone?
Norm48327 mudchicken I thought that was Trump's line.
mudchicken
May have been, but the drains got clogged!
BaltACDMay have been, but the drains got clogged!
Time to call "Rotorouter". LOL.
Paul_D_North_Jr "Weak, marginal, or too-variable subgrade bearing capacity - including expansive soils, and the heavy loads, high impact, and vibrations caused by US railroad equipment at speed, are severe challenges to any of these systems. Concrete ties - a good idea with some valid benefits - have demonstrated the sometimes-truism that "Every advantage has a disadvantage". A lot of money and faith was put into them, only to find out some years later that abrasion under the rail seat was causing wide gage and stability problems - and this weakness is ongoing. Not enough to completely negate their added value, but definitely a tarnish on it." - PDN.
"Weak, marginal, or too-variable subgrade bearing capacity - including expansive soils, and the heavy loads, high impact, and vibrations caused by US railroad equipment at speed, are severe challenges to any of these systems.
Concrete ties - a good idea with some valid benefits - have demonstrated the sometimes-truism that "Every advantage has a disadvantage". A lot of money and faith was put into them, only to find out some years later that abrasion under the rail seat was causing wide gage and stability problems - and this weakness is ongoing. Not enough to completely negate their added value, but definitely a tarnish on it."
(*) Railroaders M/W Rule #1 - Mother Nature Is A B__tch!..."
Just an observation: It seems that BNSF in this area seems to cycle their 'Heavy maintenance work' about twice a year, and other MOW functions ( Track Inspection trucks, and other maintenance a couple of more times, a year). I would have aoriginally thought that concrete ties would have been more heavily used, but, it seems they are used in odd places; in bridges, on either end (on and off?) transitions to wooden ties. Same seems to be for switches(?).
About a year ago UPRR (on the OKT sub/ nee:RI ) did a 'major maintenance push'(?) south from Wichita, rails, ties, and rebuilding of road grade crossings, grading and ditching. It seemed they had more equipment than would be used in a RBB&B Circus move.
MC mentioned seasonal problems. When I leved in SE Kansas, it seemed that UPRR was constantly, hauling large rocks to a place about a mile sout of Parsons. It was apparently, a low marshy spot,and had been for years! The KATY laid that line down in the late 1800's, one would think that they would have had that problem conquored a long time ago? But UP is apparently, still regularly dealing with it?
Seems as if the "NEW Techinques, noted by IM are just attempts to reinvent "the wheel"? I guess that any gains where ROW MOW is concerned are just simply, incremental? You gain/you loose?
MC is right in what he stated about Mother Nature...!
samfp1943MC mentioned seasonal problems. When I leved in SE Kansas, it seemed that UPRR was constantly, hauling large rocks to a place about a mile sout of Parsons. It was apparently, a low marshy spot,and had been for years! The KATY laid that line down in the late 1800's, one would think that they would have had that problem conquored a long time ago? But UP is apparently, still regularly dealing with it? Seems as if the "NEW Techinques, noted by IM are just attempts to reinvent "the wheel"? I guess that any gains where ROW MOW is concerned are just simply, incremental? You gain/you loose? MC is right in what he stated about Mother Nature...!
When you build across swamps, no matter what you do or when you do it, it remains a swamp unless you have the ability to drain ALL of it to bedrock and prevent the wet lands effects that eminate from property your company does not own.
Sam: MKT had a penchant for building in some less than choice locations. That's why their original main died an early death and they couldn't move over to MoPac trackage rights quick enough in western MO / southeastern KS. (even before the consolidation)
ps- the funny looking rip-rap on the sides of the fill around El Dorado KS is the remains of that ATSF slab track experiment of the late 70's, early 80's. .... Railroads will study a technology long and hard before allowing it in common/ universal use. They've seen what can happen with unproven technology over and over again. PTC was forced on the industry and that story is still playing out.
mudchicken Going back to the concrete tie analogy, you ought to see what happens with unconfined slab track in tension
That's going to be ugly.
"No soup for you!" - Yev Kassem (from Seinfeld)
Another case of "It aint prototype" model railroad becoming real.
BaltACD samfp1943 MC mentioned seasonal problems. When I leved in SE Kansas, it seemed that UPRR was constantly, hauling large rocks to a place about a mile sout of Parsons. It was apparently, a low marshy spot,and had been for years! The KATY laid that line down in the late 1800's, one would think that they would have had that problem conquored a long time ago? But UP is apparently, still regularly dealing with it? Seems as if the "NEW Techinques, noted by IM are just attempts to reinvent "the wheel"? I guess that any gains where ROW MOW is concerned are just simply, incremental? You gain/you loose? MC is right in what he stated about Mother Nature...! When you build across swamps, no matter what you do or when you do it, it remains a swamp unless you have the ability to drain ALL of it to bedrock and prevent the wet lands effects that eminate from property your company does not own.
samfp1943 MC mentioned seasonal problems. When I leved in SE Kansas, it seemed that UPRR was constantly, hauling large rocks to a place about a mile sout of Parsons. It was apparently, a low marshy spot,and had been for years! The KATY laid that line down in the late 1800's, one would think that they would have had that problem conquored a long time ago? But UP is apparently, still regularly dealing with it? Seems as if the "NEW Techinques, noted by IM are just attempts to reinvent "the wheel"? I guess that any gains where ROW MOW is concerned are just simply, incremental? You gain/you loose? MC is right in what he stated about Mother Nature...!
Given soft ground and shallow foundations, a wooden shack will fare better than a fine stone-built mansion. It would be pretty silly to replace conventional track on the Napoleon, Defiance and Western RR with slab track!
There are two alternatives to draining a swamp before building on it:
(i) Drive piles down to firm ground and build a platform on top of the piles, and then build on this platform. The European cities of Amsterdam and Venice were built in this way. I believe high speed lines in the Netherlands use a similar technique.
(ii) Build what effectively is a raft on top of the swamp, and put your mansion, road, railway or whatever on top of this. In the 1820s George Stephenson was faced with the problem of getting his new railway from Liverpool to Manchester, in England, across Chat Moss. Chat Moss is a peat bog up to around 35 feet deep. Stephenson solved the problem by constructing a raft from brushwood, heather, timber etc. and building his line on top of it. The line opened in 1830 and is still very much in use, still on the original raft (the acids and lack of oxygen in the peat probably prevent decay).
Plastics are useful for both (i) and (ii) because of their low density, good strength for weight and resistance to chemicals and rot. Polystyrene blocks are often used for embankments on weak ground and for waterlogged ground like swamps, would also be buoyant.
When the Southern Pacific built their mainline across marshland between Fairfield/Suisun and Benicia California the track sank within hours. They kept dumping more rock until the roadbed stabilized. Took years.
I tried to sell my two cents worth, but no one would give me a plug nickel for it.
I don't have a leg to stand on.
The tendency today is to pay more attention to the subgrade. Railroads typically devote engineering effort to the track and ballast, while accepting the sub grade as a given to deal with, other than attempting to control surface drainage. A lot of present day railroad grades were carved out before 1900. If fills needed some degree of compaction, they used water jetting saturation to consolidate the soil, eliminate voids, and then relied on drying to further shrink the soil.
For today’s highways, they carefully select fill soil type that is most ideal for achieving compaction and has the proper moisture content for successful compaction. Then they mechanically compact the soil and measure the degree of compaction to make sure it complies with compaction specs. The highway engineering extends entirely through the subgrade. They also install lots of holding ponds, tiling, and culverts to prevent the subgrade fills from becoming saturated.
A modern railroad with its intense loading no longer has the luxury of confining their engineering to just the track and ballast, while ignoring the subgrade. I doubt that the current state of the art for track construction has reached the ultimate perfection in terms of engineering or economics.
Both ballasted track and the tubular modular track system require stable subgrade to the extent that the track foundation is rigid in its supporting plane; and to the extent that that supporting rigid plane is of sufficient area to spread the weight out onto enough area of subgrade to support the trains. In other words, a subgrade can be relatively soft and flexible if the track structure base footprint is a relatively large and rigid plane. The softer the subgrade, the more area of rigid track foot base that is needed.
What ballasted track, loading is transferred from the ties into the ballast, and the bottom of the ballast transfers the loading into the subgrade. But there is no rigidity to the track foundation base at the bottom of the ballast. There is only some degree of stiffness in the ballast layer due to the interlocking nature of the rock aggregate.
With track on a concrete panel, the load is transferred to the subgrade by a rigid base footprint of the track (assuming that the panel is rigid). With the support structure of tubular modular track, those features also form a relatively rigid track foundation base. Therefore, these systems will “float” the track loading over relatively poor supporting subgrade –if- they also provide sufficient area of contact with the subgrade.
However, it may be more cost effective to properly engineer the subgrade fills than to sufficiently enlarge the track base footprint area. That would mean that if a railroad had to cross a swamp, it may be cheaper to excavate and remove the poor soil, and fill with compacted granular soil rather than build a broad footprint of track structure to float the train loading over boggy ground.
DSchmitt When the Southern Pacific built their mainline across marshland between Fairfield/Suisun and Benicia California the track sank within hours. They kept dumping more rock until the roadbed stabilized. Took years.
I believe Stephenson initially tried dumping rock in Chat Moss to form a firm foundation for his railway, but the rock just sank without trace so he had to try another strategy. No doubt SP hoped that the marshland they were faced with wasn't too deep so that dumping rock would form a solid base for their railroad. With modern techniques such as ground radar and seismology the guesswork in these matters would be eliminated.
There are circumstances in which the geology is just so difficult that the ideal construction strategy is - give up. The San Diego and Arizona Railway traversed country in which steep gorges combined with weak, weathered rock and earthquakes. In these circumstances, you can monitor the track continuously for rock falls, subsidence and earth tremors and expect to pay a lot for maintenance and even build diversions in a hurry (e.g. the Goat Canyon trestle) but in the end it may not be worth it.
mudchickenGoing back to the concrete tie analogy, you ought to see what happens with unconfined slab track in tension
Ballastless track has the same challenges as concrete highways. So the problems are not new and there are solutions: Joint spacings limiting the tensions to values smaller than the concrete's tensile strength. To avoid misalignment at joints dowels or tongue and groove constructions can be used.
The top-down production has a number of advantages. Being manufactured in precast concrete plants you usually can produce higher concrete strenth parts than in-situ. The rail fastenings can get inserted into the formwork with only little tolerances. On site large slabs are easier to align than single rail fasteners.
You need a good compacted subroadbed for slab track. Slab track is not a rigid system but an elastic slab on elastic foundation.
Slab track is not a new method. In Germany there are about 800 miles especially on high speed rail lines with more than 190 mph. In China the German company Max Boegl built approximately 3,700 miles of their slab system for high speed lines. Part of it was the line Beijing - Shanghai: https://max-boegl.de/en/downloads-en/108-ffb-slab-track-boegl-1/file.html
I think it is an interesting reed with design details and subroadbed requirements. It is just one of a number of systems I choose it here because of the good documentation.
The slab track spreads the wheel loads far better than ballasted track. There is less maintanance needed to keep high speed travel comfortable. The costs for slab track are approximately 40%-50% higher than ballasted track. The maintenance costs are less than 10% of ballasted track. Break even is said to be at about 25 years depending on system and unexpected damages. The life span is an estimated 60 years. Additional disadvantage, the slab track is about 5 dB(A) louder.
The slab track is currently not a solution for every track problem but for special purposes.Regards, Volker
VOLKER LANDWEHR mudchicken Going back to the concrete tie analogy, you ought to see what happens with unconfined slab track in tension Ballastless track has the same challenges as concrete highways. So the problems are not new and there are solutions: Joint spacings limiting the tensions to values smaller than the concrete's tensile strength.
Ballastless track has the same challenges as concrete highways. So the problems are not new and there are solutions: Joint spacings limiting the tensions to values smaller than the concrete's tensile strength.
You're getting carried away. These precast units have very little 'tensile strength' in the concrete (even where high-early-strength or additives like those in the 'concrete bottle caps' are used) and with specific reference to the Boegl system you can see the very closely-spaced control joints that in fact facilitate controlled tension cracking. Substantially all the longitudinal strength is in the tendoning, as it should be.
What MC is discussing is not so much a tendency for the slabs to 'pull apart' as for the structure as a whole to stringline. When this is resisted only by dead mass or some pathetic attempt at doweling, there will be problems just as there can be when LWR is improperly installed off the proper neutral temperature. One approach Boegl used (see p.12, I think, in the illustration of bridge trackwork) is to incorporate longitudinal keying in the precast units, and rolling or forming appropriate faces in the subgrade.
It will be interesting to see what MC and others have to say about the method Boegl uses for crossing fabrication, and for 'transitions' to conventionally-ballasted track (both of which I thought were well-thought-out from a theoretical design standpoint...)
Note also on p.15 how tuned-mass springing is incorporated in this system (it is apparently inverted compared to mine). I would like to see the precise anchoring and bedding systems used when casting the rail-seat areas in the units, and the device(s) used for finish-grinding the seat areas for fastener-hardware installation (note how the formed seat in the slab units is defined!)
There is an interesting discussion on the conversion of a 100mph line which needed rebuilding due to what I understood as being subgrade instability -- the specific details on how the subgrade was remediated here would be highly interesting.
It helps that Max Boegl is an integrated building-engineering company (perhaps comparable to Koch or Bechtel here) and not just a contractor with some experience in precast unit production.
To avoid misalignment at joints dowels or tongue and groove constructions can be used.
So train tracks will no longer have rocks under them,
How will they stay in place?
ATSFGuySo train tracks will no longer have rocks under them; how will they stay in place?
This is covered in detail in the link Herr Landwehr provided. A couple of the abbreviations used for subgrade materials and methods were not directly familiar to me, but can be reasoned out with a little more reading.
Note the difference between this method of subgrade and track provisioning and the two Class 9 systems tested for Amtrak a few years ago.
Volker Landwehr said (above): "To avoid misalignment at joints dowels or tongue and groove constructions can be used."
Those methods address only the deflection/ displacement (i.e., in the Y and Z directions) at the joint, and not the slopes or angles approaching and leaving the joint. That only guarantees that at any dip at a joint, both sides will be equally far down. Such a loss of support is not good for the ride on the rail above, depending on the depth and length.
I'd still like to know what the average and maximum 'normal' axle loads are used for the design and actual operation of such slab-track systems, as well as the speeds.
Paul_D_North_JrThose methods address only the deflection/ displacement (i.e., in the Y and Z directions) at the joint, and not the slopes or angles approaching and leaving the joint. That only guarantees that at any dip at a joint, both sides will be equally far down. Such a loss of support is not good for the ride on the rail above, depending on the depth and length.
Look at the FFL brochure pp.6-7, where they talk about the 'whipping effect' of thermal distortion.
Presumably the tremie grouting procedure after the slabs have been laid will eliminate most of the tendency for heating compression to induce 'low joints' between the slabs, as well as address any tendency for sections (e.g. those formed by controlled cracking at those control joints) to start progressively trying to tilt (like the pavement slabs on I-20)
With respect to loading: the direct-fixation system tested under the cooperative slab-track program received what I thought was considerable HAL testing, which it passed (admittedly in the very consistent TTCI environment) without substantial problem. I was hoping to find a description of Alstom NBT 'suitable for framing' in a link here, but haven't succeeded yet. But there have been a number of results of that system in 'mixed service' with positive results thus far.
Our community is FREE to join. To participate you must either login or register for an account.