How Heavy can freight cars get ? Article By Bob Tuzik
If one phrase could sum up the evolution of the North American freight car, it might be “bigger is
better.”The move to heavier cars was borne of necessity — first in key intermodal and coal corridors, then gradually on all main lines — to compete for market share that was being siphoned off by trucks and bulk freighter ships. By getting more lading into a freight car, railroads could improve their operations and their economics — and do so without having to invest in new rail lines. Car weights have increased gradually since the 1930s, but the movement made a quantum leap in the 1960s with the 100-ton capacity, 263,000-pound car. Southern Railway began hauling grain in “Big John” covered hoppers in 1963, after three years of litigation to permit rate reductions for its 100-ton aluminum cars. Burlington Northern received the first 286,000-pound cars in 1990, an order of 1,000 115-ton covered hoppers; that year it ordered 240 equally heavy aluminum rotary-dump coal gondolas. By the mid-1990s, the 286,000-pound car had become the standard on North America’s Class I railways.
A 286,000-pound car increases lading by 10 to 15 percent over a 263,000-pound car (load limits rise from 199,000 to 220,000 pounds), but the total weight on the rail grows by only 8.75 percent. Lighter-weight materials help make this possible. Approximately 1.5 million fewer 286,000-pound capacity aluminum cars are needed to haul the same tare (empty weight) per 1 billion tons hauled, compared to 263,000-pound capacity steel cars, said Joseph LoPresti, principle investigator at the Transportation Technology Center Inc., in its Annual Research Review. A oneyear study comparing the two car types on Union Pacific’s North Platte Subdivision, which links Wyoming’s Powder River Basin with UP’s Overland Route west of North Platte, Neb., yielded some remarkable discoveries: Operating 286,000-pound aluminum cars instead of 263,000-pound steel cars required approximately 1,500 fewer trains, 15,000 fewer crew starts, 770 fewer locomotives, and 29,500 fewer cars, and reduced the need for additional track and siding capacity.
Given the gain in efficiency, even heavier cars seem inevitable, especially with the demand for rail freight rising. In the three decades between the introduction of 263,000- and 286,000-pound cars, U.S. railroad ton miles increased from 621.7 million to 1,356 million. “This 118-percent increase was handled over a rail network that was concurrently shrinking from 214,387 miles to 105,000 miles, placing more tonnage over fewer routes,” explained Toby Kolstad, president of Rail Theory Forecasts, which analyzes trends in rail freight traffic and publishes the North American Freight Car Market. In 2004, U.S. railroads handled 1.5 trillion ton-miles. If they match the 30-percent ton-mile growth rate experienced in the 1990s, railroads will handle nearly 2.3 trillion ton-miles in 2025.
With capacity already strained, there will be pressure to introduce heavier loads, said Kolstad. “A 10-percent increase in lading translates to a need for 10 percent fewer cars in the fleet, essentially allowing car owners to haul as much as they’re currently hauling with fewer cars, which means fewer wheels and, one would expect, fewer expenses.”On some North American main lines, particularly coal routes, 90 percent of the traffic now moves in 286,000-pound cars. Their use has provided compelling evidence for placing even heavier cars in bulk commodity service. A 315,000-pound, 125-toncapacity (39-ton per axle load) freight car yields a 20-percent increase in capacity over a 263,000-pound car, and is a far less expensive means of managing traffic growth than adding track capacity. In tests conducted by the Transportation Technology Center, the operational benefits of 315,000-pound cars have been shown to outweigh the additional maintenance costs (about 31 percent more per year compared with 263,000-pound cars) on many main lines — except in cases where the cars would dramatically increase overall bridge maintenance costs or exceed the fatigue life (cumulative tonnage limit) of older railway bridges.
How quickly 315,000-pound cars will be adopted by the industry may depend on the findings from a 70-car test train running around a 2.7-mile loop in the high Colorado desert.
The desert bears fruit
Until three decades ago, railroads introduced heavier loads on their own properties at their own risk — often with disastrous results. The proliferation of 263,000-pound cars in the 1960s triggered a rapid deterioration of the track structure on many railroads. It wasn’t pretty, but the experience opened the industry’s eyes to the need to study the effects of further tonnage increases on a test bed where researchers could evaluate findings, and ensure an acceptable margin of safety, before the heavier cars were turned loose on the U.S. rail network.
That test bed is the Transportation Test Center, a 52-square-mile facility at Pueblo, Colo., owned by the U.S. Department of Transportation’s Federal Railroad Administration and operated by the Transportation Technology Center Inc., a wholly owned subsidiary of the Association of America When heavy cars meet inadequate track, something might end up in a ditch. the beatings from loaded coal trains proved too much for the 90-lb. rail (rolled by U.S. Steel’s Gary Works in 1910!) on a branch line south of Rockford, Ill., in spring 1997. Incidents like this were common before Dot-conducted heavy axle load tests A broad range of tests on rolling stock, track components, signals, safety devices, and vehicle performance parameters are conducted on 48 miles of track and in laboratories at the Test Center. But it’s that 2.7-mile High Tonnage Loop track (shortened from the original 4.8-mile oval to concentrate more tonnage on the track) that has rendered the facility uniquely qualified to perform tests on heavier freight cars.The Heavy Axle Load testing program conducted through the Facility for Accelerated Service Testing (FAST), with funding by the AAR, the FRA, and contributions from the railroad industry, was instrumental in successfully introducing 286,000-pound cars into revenue service. FAST moved to the transportation department’s Pueblo center in 1976 [see “The Train That Goes Nowhere … FAST,” May 1993 Trains]and began conducting heavy axle load tests of 315,000-pound cars in 1988, at the behest of the railroad industry.“Tests done by an individual railroad, even one the size of the Union Pacific, might be dismissed as an anomaly,” explained David Connell, chief engineer for Union Pacific’s Central Region. “Having an unbiased lab with the ability to perform comparative tests has forced the supply industry to move forward much faster than they otherwise might have.”
The 70-car test train, typically powered by four locomotives, makes an eight-hour run around the High Tonnage Loop, alternating directions each day, at an average speed of 40 mph. The main focus of FAST’s heavy axle load tests has been on the impact of 315,000-pound, 125-ton carloads on track components and premium suspension systems for heavier cars, with a goal of determining the economic costs and benefits of operating heavy axle loads. Early tests of 315,000-pound cars at the Transportation Technology Center produced track failures that could have shut down a main line or drained a
maintenance-of-way budget. A switch point in a No. 20 turnout cracked after only 5 million gross tons (mgt) of traffic. After 15 mgt, rail wear on unlubricated curves increased, compared with 263,000-pound-car wear rates. Applying trackside lubrication devices and installing head-hardened rail brought down the rail wear in the gauge-face on , but caused a substantial increase in vertical rail-head wear. A “hellacious” number of field weld breaks were reported, and surface anomalies such as rail joints, low spots, and engine burns resulted in “rapid and severe” degradation. Most daunting of all, perhaps, spot track maintenance increased 66 percent, and overall maintenance by about one-third.“We’d rather shut down the TTCI than shut down service on a revenue railroad when something goes wrong,” said Bill Wimmer, vice president of engineering for Union Pacific. “We agree as an industry that new, critical components, such as new tie types, fastening systems, and thermite welds should be tested at the TTCI before we put them into revenue service.”
There may be no answer to the question, “How heavy can freight cars get?” but results from the Transportation Technology Center’s heavy axle load tests are answering perhaps a more important question for the industry, “How heavy can freight cars feasiblyget?” What follows are some of the findings from 17 years of heavy axle load testing, which suggest how railroads might upgrade and maintain their rights-of-way to accommodate 315,000-pound cars.
Good rail is fundamental
Nearly 700,000 tons of rail are replaced each year by U.S. railroads, at an annual cost of about $400 million — one of the largest capital expenditures in the industry. With the cost of rail skyrocketing, extending its life has taken on even greater importance.
Rail is typically replaced because of fatigue or wear — head wear in tangent track, gauge-face wear in curves. Heavy axle load testing has shown that wear, deformation, and fatigue-resistance are strongly influenced by the hardness and metallurgical micros structure of rail steels. In simple terms, clean, head-hardened rail is more resistant to wear and fatigue damage than standard carbon rail, especially in curves.Rail is measured by its Brinell hardness (Bhn), which indicates the resistance to indention by a steel ball under hydraulic pressure. Hardness has gradually increased over the past 50 years from approximately 260 Bhn for standard carbon rail to more than 400 Bhn for some premium rails. In the early 1950s, head-hardened, heat-treated rails were introduced, in which the top and sides of the railhead are heated, quenched, and control cooled to produce a microstructure that results in a higher hardness and tensile strength than that of standard carbon rail [see “Ribbons of Steel,” December 2004 Trains].Today, North American railroads typically use rails in the 300- to 320-Bhn range for tangent track and lighter density applications. Premium rails,which the American Railway Engineering and Maintenance of Way Association characterizes as 341 Bhn or greater, are often used in curves or other demanding applications. Fully head hardened rails in the 380- to 405-Bhnrange are used selectively in areas of high curvature on lines subject to heavy axle loads. Very-high-hardness rails in the 420- to 430-Bhn range are currently being tested.
Metallurgical cleanliness, which is determined by the number of “non-metallic” inclusions that can lead to rail surface defects, has also improved significantly in the past half-century. Research conducted by the Transportation Technology Center has shown that the use of clean steels can increase the life of rail by a factor of five or more. Improvements made to rail steels, spurred in part by tests performed at FAST from the late 1980s through the 1990s, have led to a 100-percent increase in rail life on tangent track and mild curves, and a 150-percent increase in rail life in moderate curves. At current traffic volumes, this increase in rail life represents savings of hundreds of millions of dollars per year (including installation costs).Welding for longer lifeAlthough component suppliers have supported the efforts of heavy axle load testing by donating materials, they haven’t always been pleased with the results. Thermite weld manufacturers, for one, were alarmed by the initial 90-percent weld failure rate under the 125-ton cars operating at FAST. But like the makers of rail and other track components whose materials have taken a beating there, they went back to the drawing board and found ways to make their products better withstand the heavy axle load operating environment.Thermite, or field, welds are produced by a chemical reaction of aluminum with a metal oxide. A primary concern with their use is that the weld material is typically softer than that of the rail steels; this tends to create a soft spot in the rail, causing a discontinuity in the rail surface. As rail hardness has increased, manufacturers have worked to achieve a matching hardness in thermite welds. Field welds do not perform as well as other types (such as rail plant or electric flash butt welds), but they’ve come a long way. Researchers at the
Transportation Technology Center are evaluating head-hardened field welds in addition to other new techniques, including gas pressure welding, which is widely used by Japanese railways.
Diamonds are not foreverAs cars get heavier, special trackwork, such as crossing diamonds and turnout components (e.g., frogs and switches), can incur severe damage. One early FAST test evaluated the ability of standard track components to withstand 160 million gross tons of 125-ton heavy axle loads. The results were grim. Highimpact components such as diamond crossings exhibited severe wear and/or deformation, required significantly more maintenance, and in some casesfailed altogether.Based on the results, an AAR committee scheduled a second round of tests incorporating improved, or “premium,” track components donated by suppliers. While the heavy axle load test train continued to deliver a pounding, the premium components held up much better, providing evidence that heavy axle load traffic could be accommodated on conventional track — if premium components were used for high-wear and high impact conditions and an appropriate maintenance program was in place.As part of the heavy axle load tests, the Transportation Technology Center studied the effects on switches and frogs. Researchers tested high-integrity frogs, premium components, and improved turnout geometries (e.g., lower switch entry angles). The testing enabled manufacturers to make modifications designed to prolong the life of special track work components. The average service life of No. 20 frogs, a standard mainline size, increased from 340 mgt to 595 mgt under 286,000-pound car loadings between 1990 and 1998. By modifying the running surface profiles and contact points of fixed-point frogs, turnout maintenance required under 315,000-pound loads at FAST has actually decreased by about 50 percent over the past 10 years — a far cry from the initial heavy axle load test results.“We’ve greatly improved the service life of frogs and other track work through the efforts of HAL testing,” said Bob Blank, Norfolk Southern’s director of research and tests. “We’ve also seen a lot of innovation with regard to switch-point design and the flange bearing crossing diamond.”Flange-bearing crossing diamonds incorporate shallow, tapered flange ways that make contact with the bottom surface of the wheel flanges instead of the wheel tread surface — in effect lifting the wheel tread off the rail, while guiding the flange through the diamond. This eliminates impacts with intersecting flange ways through the crossing. FAST tests confirmed that the wheel flange could safely support heavy axle loads. Another new type of crossing diamond tested at FAST features ramped running surfaces on either side of the crossing frog, which can reduce the rail end batter typically associated with diamond crossings up to 40 percent. Both types of diamonds have proven successful at reducing impact and wear, and have been placed in revenue service on several North American railroads.The tests have also helped the industry move down the road to component standardization. “We used to use five or six different types of rail anchors,” said Union Pacific’s Wimmer. “By testing at FAST we found out which ones really had holding power and which ones didn’t.”Crosstie tales Crossties and fasteners, the building blocks of track, were tested at FAST to determine their lateral strength, or gauge-holding ability. The gauge-holding performance characteristics of ties is measured as a function of tonnage. Since about 90 percent of the ties inserted annually on North American railroads are made of timber, the industry was interested in measuring the ability of elastic fasteners to hold gauge on timber tie track under heavy axle load traffic, particularly on curves. In 1999, the Transportation Technology Center conducted a wood tie and fastener test, comparing common railroad spikes with two types of elastic fastening systems on both softwood and hardwood ties. In test sections on 5- and 6-degree curves, the elastic fasteners consistently outperformed the cut spikes.Union Pacific began installing elastic fasteners on tightly curved timber tie track after a series of FAST tests. “The TTCI was able to replicate our loading conditions fairly well and prove the benefits of using elastic fasteners to control gauge widening,” said Union Pacific’s Connell. “What we learned directly from the tests at FAST in this area is one of the biggest things that helped us move forward in the successful operation of heavy axle loads on our own railroad.”As concrete ties have become commonplace on high-tonnage freight lines, railroads have seen more examples of rail seat abrasion — where the tie area directly beneath the rail base becomes worn away — a potential safety issue. To see what might be done to address the problem, the Transportation Technology Center replicated naturally occurring moisture and abrasion conditions in various parts of the country. With the help of tie, pad, and fastener suppliers, technology center engineers evaluated repair techniques and tested new wear pads and embedded plates, which have become standard issue on concrete tie track on most railroads today.CSI … PuebloSometimes, things do go wrong. In 1994, while testing a new fastening system being actively marketed to the railroads, a derailment shut down FAST’s High Tonnage Loop for 35 days. Because there was no pressure to get revenue trains running again, a detailed investigation and analysis was able to be conducted to pinpoint the exact cause of the derailment. Axle failures have caused three other derailments at FAST between 1998 and 2001. After each one, Transportation Technology Center researchers conducted forensic work into the causes of the axle fatigue and the heavy axle load environment. A metallurgical examination found that each axle failure initiated at surface damage to the axle. As a result, the Transportation Technology Center designed a new fixture for handling axles, and began ultrasonically inspecting axles in the heavy axle load test train twice a year. Railroads took notice and have begun re-evaluating their own axle inspection and handling procedures. A new research program will begin looking at improved axle designs.Where the wheel meets the railRail grinding has been performed on mainline railroads for decades, but only recently has the industry become more attuned to how rail profile grinding patterns and frequencies might be adjusted to account for rail hardness, wheel and rail profiles, rail lubrication, train speeds relative to curve designs, and other factors associated with wheel/rail interaction. By controlling the contact angle between the wheel and the rail, the potential for wheel climb, and consequently rail fatigue or wear, can be diminished.“Most railroads had a poor knowledge of wheel/rail interaction prior to the FAST/HAL rail profile grinding tests,” said Norfolk Southern’s Blank. “They didn’t realize the importance of having compatible wheel and rail profiles to minimize contact stresses and wear, or the effect of friction on wheel/rail interaction.”Heavy axle load testing made it clear that railroads had to look closely at wheel/rail profiles and their maintenance if they were to operate 286,000-pound cars successfully. Norfolk Southern took the lesson to heart and adopted the Wheel Rail Tolerance software developed by the Transportation Technology Center to guide its rail profile grinding.Sophisticated grinding techniques alone won’t reduce the rail and wheel wear from heavy axle loads on curved track. An effective rail lubrication/friction management system is just as critical. Years of heavy axle load testing has shown that effective gauge-face rail lubrication on curves and top-of-rail friction control can reduce lateral curving forces by 25-50 percent, and energy consumption by 7-25 percent. (Closed-loop testing at FAST yielded a 32-percent reduction in fuel consumption.) These enBattered rail ends are visible on this crossing diamond after 150 million gross tons of revenue service and high-impact pounding. Investigation of broken-axle derailments at FAST has led to improved axle inspection and handling procedures industry wide.
Bigger and Heavier Freight Car capacity
How Heavy can freight cars get ? Article By Bob Tuzik