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State of the Art in Wheel/Rail Control:

Highlights of the 1999 International Heavy Haul Specialist Technical Session

Michael D. Roney General Manager Engineering Services and Systems Canadian Pacific Railway SUMMARY The 1999 specialist technical session on wheel/rail control sponsored by the International Heavy Haul Association held in Moscow, Russia covered many aspects of practices used by bulk haul railways around the world to control wheel and rail wear and vehicle and track dynamic interaction. This paper discusses the author's impression of the emerging "best practice" that was reflected in the papers and discussion at this conference. World class heavy haul railways are characterized by impressively low fuel consumption, long wheel lives and low rail renewals. Some of the common features of emerging best practice discussed are preventive rail profile grinding to conformal profiles, limits on wheel tread hollowing, wheel impact detectors, harder, clean rail steels rolled to an 8 in. head radius, high cant tieplates, positive restraint fastenings, spring or swing nose frogs, tangential geometry turnouts with integral baseplates, engineered track transitions, lubrication management and steerable trucks on cars and locomotives. Key words : vehicle/track, track dynamics, vehicle dynamics, vehicle/track interaction, track technology

1. INTRODUCTION In June of this year, the International Heavy Haul Association put on a workshop in Moscow, Russia, on the special topic of Wheel/Rail Interface. 250 delegates from 17 countries presented papers and discussed the state of the art in controlling interaction between the rail and wheel and vehicle and track. Wheel/Rail Interface was chosen as a topic of special interest to heavy haul carriers around the world as it has been felt by many that good engineering can result in substantial savings in the cost of railway transport of bulk goods. What came out of this conference is likely the most intense treatment of vehicle and track behaviour as affected by contact conditions that has ever been put forward. And of particular interest is that a "best practice" appears to be finally emerging among railways everywhere. In this presentation, I hope to capture my interpretation of what this conference put forward as the vision of the "best practice" bulk haul railway of the present and future. The presentation is organized in three parts: 1. 2. 3. Lessons for track design Best maintenance standards for heavy haul track Mechanical changes that will drive down track costs.

2. LESSONS FOR TRACK DESIGN 2.1 Rail The conference had several papers dealing with new developments in rail metallurgy and one on improvements in rail section design. They gave a pretty solid endorsement of the value of today's harder, cleaner rail steels. The best rail steels available today were reported to hold their profiles well and to be

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substantially better at resisting fatigue and corrugations than steels available a decade ago. But there was a feeling that we are close to reaching the limits on what additional economies can be achieved with conventional pearlitic rail steels. Test results with bainitic steel microstructure showed improved fatigue resistance achieved through higher hardness and yield, though less wearability than pearlitic steels for the same hardness. This could make them suited for a lubricated environment, where water and lubrication increase surface cracking while greatly reducing wear. Low alloy hypereutechtoid steels are also challenging the conventional microstructure with results showing both higher wearability and improved fatigue resistance for a premium. Tomorrow's rail will likely be substantially improved over today's. Corrugations are already a thing of the past on most heavy haul railways. With the emphasis on steels with improved fatigue resistance, spalling may be the next to go. Extended wear limits are becoming commonplace as railways adjust to better rail metallurgy, but further improvements in life will likely result from the use of rails with greater mass in the head. Studies are showing substantial reduction in the internal stresses that contribute to rail fatigue through use of larger web/fillet radii. Once fatigue is under control through rail grinding and clean steel metallurgy, wear life is extended almost in direct proportion to the depth of the rail head . So the rails of the future will be very similar to the 140lb. section being proposed by AREMA Committee 4, which is compatible with the 136lb. web and base, but is 7/32" deeper in the head. This latter effort also highlights a healthy trend in the industry: railways seem more amenable than ever to achieve standardization on what they will buy. The industry appears finally to be converging on an 8 in. rail head radius, including believers as far away as the Brazilian Mining Railways. The 8 in. radius is a stable shape that most closely reflects how railways have found they need to grind the rail to control steering and reduce fatigue under varying rail rollover conditions, so it has followed that this is how the rail should be rolled to start with. 2.2 Crossties and Fastenings There was little of specific recommendations on crossties, but a growing awareness of the need for positive restraint from fasteners to counter the occasional L/V's recorded that produce dynamic overturning moments that pass outside of the base of the rail. Overseas heavy haul railways are unanimous in their use of direct fixation fastenings. In most overseas applications, economics favour engineered crossties such as concrete. In North America, a major deterrent is the cost of out-of-face replacement required to convert existing timber trackage. Timber was cited for its natural resilient properties which assist in dampening out unfavourable dynamics, but over the long term, the relative price escalation of timber vs. concrete has left many authorities favouring synthetic crossties for new construction. An emerging consensus of the conference centred upon the most favourable rail cant. It is now fairly widely acknowledged that a higher rail cant improves contact conditions on the high rail of curves. It both reduces heavy gauge corner contact and improves effective wheelset conicities, which promotes steering. On the low rail, on the other hand, field side contact is usually unfavourable. So high cant plates are not recommended on the inside rail of curves. In tangent track, the objective is usually to avoid flange contact, which promotes truck hunting. So, remarkably, this conference seemed to settle, through the consensus of both Australians, French and at least one North American on the following standards: 1 in 20 cant on curve high rails 1 in 40 cant on low rails 1 in 20 cant on tangents.

2.3 Turnouts It is typical of international conferences that the Europeans admonish the North Americans for our turnout geometries, likely with good reason. In fact, most heavy haul railways have chosen a more expensive design of turnout than the AREMA standard, trading this off against reduced maintenance costs. It was illuminating to this observer to see how many authorities had standardized on swing nose frogs and tangential geometry turnouts in high density trackage. Many North American designs have incorporated a "pseudo-tangential" design which gains the benefit of reduced lateral forces within a more limited switch

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point length, while incorporating greater mass at the point of impact. The re-emergence of the spring frog in North America is another lower cost response to the swing-nose concept. Integral baseplates are also a standard borrowed from overseas that is showing very strong improvements in turnout life. While European designs might favour an all-welded turnout, the North American mitred heel design of frog casting (Figure 1) was cited as an interesting approach to reducing dynamics. In this design, the wheel never encounters a gap, so it doesn't impact the casting and rebound as secondary batter.

Figure 1 Discontinuities represent a cost to a high tonnage railway that can be managed through attention to welding and use of anti -impact measures such as the mitred heel of frog castring illustrated here

An Australian paper on turnout grinding initiated thoughts about canted baseplates. The Australian illustrations of rail gauge corner spalling at locations where the wheels meet the gauge corner on flat plates looked remarkedly similar to North American experience. With today's sophisticated manufacturing, it is feasible to maintain the same rail cant in the turnout area as on the adjacent running rails, eliminating the tendency for the change to flat plates to initiate lateral loads. 3. MAINTENANCE STANDARDS FOR HEAVY HAUL TRACK 3.1 Gauging A characteristic of heavy haul track is that it is rarely maintained to "minimum standards". This is "bread and butter" infrastructure whose maintenance should be dictated by what reduces costs. So it should be no surprise that some of the work presented at the Heavy Haul conference suggested that maintenance standards should be well within safety standards. Papers at the conference cited gauge greater than ½ in. as significantly contributing to rail damage, inferring that under current wheel conditions, gauging would be cost justified. At the same time, it was shown how gauge narrower than ¼" less than standard would start to increase wheel wear. Whether this became a major cost driver or not would of course depend on how many wheels are condemned from thin flange, but fuel consumption was cited as a factor.

Figure 2 Wide Gauge exceeding ½ in. is seen as contributing to significant rail maintenance

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3.2 Rail Grinding In North America, we are in a debate about how much grinding is enough. It was interesting to see at this conference how some other authorities were attempting to cope with much less grinding capacity than we are used to. For example, a Russian Railways representative openly related their 10 mm (< ½ in.) maximum wear limit in 60 kg/m (120 lb./yd.) rail to flattening of the low rail and consequent surface fatigue damage, which they would hope in future to overcome through rail profile grinding. It was clear that rail grinding practice has evolved to the level of an integral part of rail management in North America, Australia and South Africa. There was some evidence presented that directly related rail surface cracks to the risk of internal defects. As surface cracks grow in length, their rate of growth increases. At 10mm (< ½ in.) depth of crack, some findings cited a tendency to grow in the transverse plane to initiate transverse defects. This gave some justification to frequent preventive grinding. On the other hand, TTCI tests have implied that greater grinding intervals are similarly effective at controlling fatigue. Some rationale for this difference may be attributed to observations that fatigue is more prevalent in higher moisture environments, particularly in conjunction with lubrication. Stiffer track structures, such as concrete ties also require more frequent grinding. Grinding of the high rail has been a chronic debate in North America. There have been the proponents of heavy gauge corner grinding which results in "two-point contact" and eliminates loading of the corner and subsequent fatigue. At the other end of the spectrum are those who espouse single point contact, where the wheel rides the gauge corner contact for maximum steering. The conference cited examples where one and two point contact profiles on the high rail would be appropriate given the prevailing conditions, but it was generally illustrated that an aggressive 2-point contact would significantly increase wheel and rail wear rates and be an unstable wheel/rail match. A gentle 2­point contact would be appropriate where rail steels would flow or rail cant would vary. But in general, the best balance between wheel and rail wear as well as rolling contact fatigue was demonstrated to be achieved via a single point conformal contact, particularly on premium rails, with their lower rates of plastic flow.

Severe two point contact


Single point contact

Conformal contact

Figure 3 Illustration of different high rail/wheel flange contact conditions - conformal contact minimizes wheel and rail costs


Having said this, it is apparent that reshaping of the low rail or correction of low rail surface grinding is the prime driver of grinding requirements on most properties. A broader contact band was advocated on the low rail by heavy haul railways who have licked the wheel hollowing problem, but was generally seen as desirable in spreading the loadings out over more metal area and reducing low rail surface fatigue. And ironically, Australian practice has demonstrated that in tangent track, where track hunting and yaw resonance of cars is made possible by longer tangent sections, a pronounced gauge corner grind is prescribed. This is because 2-point contact eliminates the influence of the high conicity gauge corner contact, which forces the wheelset to the opposite rail. Another interesting practice discussed at the conference was the possibility of deliberately shifting the contact band around on the tangent through

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grinding to spread the contact over different parts of the rail head, with purported benefits in rail surface fatigue, wheel spalling and tread wear. Another positive influence of harder, cleaner rail steels is that they should require less grinding. When ground to templates that reflect natural wear patterns, i.e. conformal contact, their shape remains stable and requires less grinding to compensate for plastic flow. Harder rails require tighter tolerances on the profile, but with the right shape and the right yield strength and cleanliness, alloyed heat treated rail steels have the capacity to withstand today's loadings without premature fatigue. If they must be reshaped frequently, the grinding template is wrong. 3.3 Track Geometry In addition to gauge, there are other practical implications for geometry standards for very heavy haul track. These might be very simply distilled into two simple rules: 1. 2. Avoid joints, particularly in curve transition spirals. Engineer track transitions.

The first point is obvious. Under the heavy loading and lower speeds of heavy haul tracks, most geometry defects are related to loss in track support at joints or other discontinuities. In world practice, some authorities take joint elimination very seriously while others do not. The track transition issue is more subtle. Where track support stiffness changes abruptly, as between wood and concrete ties, or at a bridge approach, the travelling wave ahead of the train tends to uplift the ties and skew them. At least one paper highlighted the growing awareness of the need to provide stiffness transitions to maintain track integrity. Best practice would call for a high tonnage railway to incorporate some of the following types of engineered transitions: n n n n n n n use of overlength ties at bridge approaches. intermixing concrete or steel ties with timber in advance of a premium sleeper section concrete slabs cantilevered from bridge approaches and tapered to ramp up stiffness under the adjacent track support. use of softer, thicker pads on concrete sleepers adjacent to timb er and in tunnels; addition of sleeper pads on timber track on bridges and through crossings at grade;. addition of hot mixed asphalt under the ballast at bridge approaches. Carrying elastic fastenings from bridges into the adjacent track section

Figure 4

Transitions between different vertical sttiffnesses are high maintenance locations that can be addressed by engineering transitions

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Figure 5

World heavy haul railways prefer engineered premiun ties, with particular attention to stiffness transitioning bewteen synthetic and timber ties

Interestingly, underbalanced curve elevation was demonstrated to be desirable in promoting steering. The Chinese Railways have settled on 15mm (>1/2 in.) in underelevation , while most North Americans waver between 1-2 ins. unbalanced. 3.4 Turnout Repairs While the author would see rail grinding practice as a particular strength of North American "heavy haulers", it is ironic that hand grinding and weld repairs to special trackwork receives a much greater emphasis overseas. Europeans in particular see timely in track weld repairs as integral to managing the life of castings. The Russian Railways have actually automated the practice to a large degree using a rig that attaches to the frog to guide the electrodes. Welding and weld repairs is seen as more of a necessity and an integral maintenance practice. As part of the conference, the delegates visited the Russian Railway's research facility and witnessed use of powder metallurgy techniques to grind out and rebuild engine burn defects. It was clear that welding expertise was valued as a "core competence" of these heavy haul railways. On the other hand, North American railways have embraced switch and crossing grinding to a greater extent, as a way to correct and relieve distress over most portions of the switch area. Mechanization of the practice may be the particular allure, as opposed to the more labour intensive, but arguably effective rehabilitation of the turnout area through hand grinding and of in-track welding. 3.5 Defect Management The flip side of extended rail life is the management of the risk. As covered in one paper, the past decade has seen continuous advances in rail testing accuracy and reliability, plus a concerted attempt on behalf of heavy haul railways to tighten testing intervals. As a general statement, risk of rail failure has reduced.

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But it is not all improved reliability of testing. Various papers addressed how steerable trucks would reduce surface fatigue and hence internal defects, and how restressing would reduce the tendency to develop transverse defects. Certainly, the Russian Railways confirmed the relationship between cold weather and the incidence of rail failures, due both to rail in tension, and the reduced fracture toughness of some rail steels. As a bottom line, it was seen to be most prudent to recognize a certain level of risk and to adjust rail testing intervals to adjust detection reliability in line with the ris k of rail fracture, as the most effective strategy at maintaining rail service reliability. 3.6 Control of Truck Hunting The more tangent alignments of the world report a preoccupation with maintaining a stable ride for bulk haul trains. Truck hunting and the continuous nosing action of cars in a yaw resonance mode represent significant concerns for some railways. Some of the solutions that have been put forward are: 1. 2. 3. 4. 5. Add 4mm of unbalanced elevation in tangent. Plane rail to eliminate the curve wear pattern in the rail, particularly rail flow to the field side of low rails. Tamp to remove the memory of where wheel flanges typically force the rail out and down Maintain 2 point contact conditions in tangents through grinding Speed restrict to less than 50 mph

OR, get at the root cause by maintaining friction wedges and their wearing surfaces on trucks subject to hunting. Measurements show that the capability of the truck to dampen out sustained nosing action have dropped to 40% before the friction rise is condemnable by AAR Interchange standards. 3.7 Lubrication AAR studies in the early 80's got railways' attention with reports of threefold reductions in rail wear with lubricated rails and measured fuel savings. Conrail was an early convert, but railways in general have not generally adopted friction management as a prime focus. Two of the papers at the conference dealt with the benefits of lubrication with some convincing results that again highlight lubrication as a "best practice" that can have greater savings than railways currently exploit. A report cited work on wayside detector effectiveness on the Norfolk Southern, where 20 new lubricators were installed on an 80 mi. length of line, replacing 49 existing lubricators. Some wiping bars were extended up to 55 ins. On other bars, the size of the outlet ports was reduced, but the number of points along the wiping bar was doubled. TTCI reported reduced gauge face wear and elimination of train stalls. TTCI predictions using their NUCARS model peg fuel savings up to 13% when the top of rail is lubricated. The high rail and low rail friction must be in balance, however. High lateral loads were predicted when the gauge face is lubricated, but the top of both rails is dry, or when the top of the high rail is lubricated, but the low rail is quite dry. TTCI's guidelines can be stated as: · · · · Maintain top of rail friction coefficient differential, left to right <0.1µ Maintain top of rail friction>0.30µ If the top of the high rail becomes lubricated, lubricate the low rail too. Maintain gauge friction coefficient of <0.25µ

Recently, hi-rail powered tribometers are available that can survey both top of rail and gauge face friction continuously over a subdivision. Periodic surveys of lubrication effectiveness in correlation with rail wear rates and subsequent respacing and /or upgrading of lubricators could be considered as a current "best practice".

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Figure 6 Measurement of top of rail and gauge face friction and subsequent adjustment of wayside lubricators is an emerging trend among heavy haul railways.

4.0 MECHANICAL CHANGES THAT WILL DRIVE DOWN TRACK COSTS Arguably the most effective thing a track engineer can do to improve track is to get poor performing freight cars set off. Our mechanical partners have done marvelous things to design more efficient locomotives and lighter cars, but I frankly do not see the same improvements in regular freight car maintenance practice. If there was one thing that was driven home at the Moscow conference, it was that track and freight cars are a system. What works for one usually works for the other in reducing wear and fatigue and ensuring safety. But if one is not well maintained, the other suffers as well. 4.1 Locomotives So let me talk first about some of the lessons of the conference on the locomotive front. AC locomotives and steerable trucks figured prominently in visioning the future for non-electrified heavy haul railways. AC locomotives were reported to be capable of achieving 35-38% traction during normal running, and 48% on starting to lift a train. They are also reported to be less sensitive to surface contamination of rails. M/W folks may have some concern about surface fatigue cracks that usually accompany high tangential loads, but may grind these out. On the other hand, they will applaud the steerable trucks featured on the new units. The mechanical advantage is less wheel wear and a 10% adhesion increase in a 10 degree curve from less slippage. The engineering advantage is less rail wear and less stress on fastenings. A presenter from EMD predicted that AC locomotives with steerable trucks would ultimately find their way into widespread diesel-electric freight service. An Indian Railways representative held a dis senting view, cautioning that many of their bridges would need to be strengthened to handle the increased longitudinal forces. 4.2 Wheels

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Wheels are manufactured with the same high carbon pearlitic microstructure as rails. In North America, the majority are Class C wheels with a hardness between 321 and 363 BHN. Thus makes them compatible in hardness with premium rail steels used in curves, which would seem to provide the best balance in wear. But wear tests reported by the French and the Russians demonstrated that rails with greater hardness did not necessarily sacrifice a softer wheel, and vice versa. It is disturbing to hear that wheel spalls are surpassing tread wear as the major cause of wheel removals, but good to see a broad trend towards reduced flange wear. Spalled wheel treads are usually associated with wheels that tend to adopt a misaligned position on the rail, or "angle of attack" that causes shear stresses on the surface of wheel and rail. It can also be a result of wheel sliding from stuck brakes. The tendency for a wheelset to adopt a skewed approach to the rail may have started as a misaligned brake beam that puts too much pressure on the given wheel. Once a slight hollowing is set up, it tends to become worse with time. Spalls appear to grow faster in the presence of moisture, as in winter conditions. A Brazilian paper demonstrated how many misaligned trucks never regain a straight orientation after exiting the curve into tangent track. They have found, as was shown in Canada, that steerable trucks reduce spalling by aligning the wheelsets radially to the curve. TTCI reported on some very interesting work on the economic costs of permitting wheel tread hollows to develop. Unlike Europe, Australia and South Africa, there is no standard in North America on how deep a wheel tread may be permitted to hollow. This is the flipside of typical rail grinding standards which call for grinding when the low rail becomes too flat. TTCI's survey of 6,500 wheels found that 6% had more than 3mm of wheel tread hollowing. They also predicted that wheel with 3 or more mm of wheel hollowing had a large effect on train resistance and hence fuel consumption, and imparted higher forces in tangent and low curvature track. A large cost of damage to special trackwork is also speculated due to the high stress impacts of the wheel's "false flange". Inclusion of wheel hollowing as a wheel maintenance standard is being pursued by TTCI through the AAR.

Figure 7 Heavy haul railways with wheel lives considerably longer than the norm in North America maintain maximum limits on wheel tread hollowing.

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The Australians and South Africans jousted for bragging rights on their average wheel lives, and indeed these are impressive by North American standards. Spoornet, the South African Railways, reported that 1 million miles was the average life for a 2 wear wheel, with many exceeding 1.5 million miles. This compares to about a 320,000 mile average here. These long lives are achieved through regular turning of wheels on a lathe to restore the profile, akin to rail profile grinding. Very little metal needs to be removed at each turning. So, for example, the South Africans will make 5 cuts of a wheel over its life, with an obvious benefit in maintaining a good profile . A prime deterrent to this practice in North America at present is the regulation that bearings must be inspected at each wheel turning, so wheels are likely to be replaced anyway to assist in the inspection. Expect this to change in the future. Several papers, including one from the Ukraine showed the value of wheel profiles that were more conformal to the rail. This is a fit with the consensus of maintenance of way delegates, who advocated a broader, conformal rail profile in curves. The Russians gave results on a common wheel maintenance technique that they have adopted. Their wheels are periodically treated by gas plasma. In gas plasma hardening, the wheel surface is heated rapidly by a high energy jet of low temperature nitrogen plasma. When the wheel cools, which occurs rapidly because of the large mass of the wheel, the surface of the wheel is quenched and a hard martensite forms. This is effect provides a regular heat treatment as the wheel wears and is reported to extend service life. They also demonstrated laying welding beads on wheel treads to build up their service lives. 4.3 Trucks In most railway applications the economics of the inexpensive three-piece truck, built up from castings, are difficult to beat. But in the high mileage heavy haul environment, railway operators can afford to pay more up front for features that reduce rail and wheel costs, and concomitant fuel consumption. Again, steerable trucks, also known as frame-braced or radial trucks, have been the usual choice of premium truck for heavy haul operators, particularly those in higher curvature territories. Steerable trucks reduce angle of wheelset alignment, reducing tread friction, fuel consumption and spalling. They can also improve stability in tangent track. Tests at TTCI has shown this feature to be the most effective of options for premium trucks. Some degree of steerability is also possible by adding shear pads between bearing adapter and side frames, but this is less effective. TTCI tests have also shown that the steering performance of radial trucks is hampered by severe two point contact conditions. The future should see better performing steerable trucks with added load attenuation built in to reduce dynamic impacts on rail and trackwork. Several papers dealt with emerging technologies aimed at diagnosing poor performing trucks. For example, angle of attack measuring devices exist which, with varying degrees of success, highlight trucks which are obviously imposing high lateral loads. 5. CONCLUSION Heavy haul railways around the world have made very impressive gains in reduced rail and wheel costs and fuel consumption over the past 20 years. Much of this has been the result of an improved technical understanding of the wheel/rail system and the dynamic nature of vehicle/track interaction. A standard practice appears to be evolving for heavy haul railways that shows equivalent results remarkable consistency around the world in spite of a large variation in different service environments. Based upon the lessons of the Moscow conference, the heavy haul railways of the near future will be characterized by: electrified or AC traction high adhesion locomotives steerable trucks on cars and locomotives truck maintenance standards tighter than AAR interchange rules truck and wheel performance diagnostic systems maximum limits on wheel tread hollowing

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frequent wheel reprofiling improved control on brake application direct fixation rail fastenings deeper rail heads rolled to 8 in. radius in clean, harder steels frequent, preventive rail grinding tangential geometry turnouts, spring frogs or swing-nose frog designs engineered track stiffness transitions all-welded or mitred rail discontinuities

Figure 8 World record for the heaviest train ever pulled was BHP Iron Ore's 630-car, 70,000 ton test consist in the Pilbara region of northwest Australia

6. REFERENCES Kerr, A. and Moroney, B. E., Track Transition Problems and Remedies, Bulletin 742, American Railway Engineering Association, pp. 267-297, Washington 1996. International Heavy Haul Railway Association, Proceedings of the 1999 STS Conference "Wheel/Rail Interface", Moscow, June 1999, Vols. 1&2. International Heavy Haul Railway Association, Treatise on Wheel/Rail Management, 2000 (not yet published). The proceedings should be out in January 2000 and there will be two volumes. They can be ordered by contacting IHHA at e-mail [email protected] or by fax 757-496-2622 or mail, IHHA, 2808 Forest Hills Court, Virginia Beach, Va.. 23454. The price has not been set at this time but should be in the range of 75USD for each volume. You have your first volume as an example.The treatise will be out in late 2000, no price at this time.

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State of the Art in Wheel/Rail Control: Highlights of the 1999 International Heavy Haul Specialist Technical Session

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