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Sussmann is Civil Engineerand Choros is MechanicalEngineer, Volpe NationalTransportation SystemsCenter, Cambridge,Massachusetts. Read isPrincipal Investigator(retired), TransportationTechnology Center, Inc.,Pueblo, Colorado. Farritoris Professor, Mechanical andMaterials Engineering,University of Nebraska,Lincoln.

R ailway track innovations historically havefocused on track structure support.Although track structure is simple, improv-

ing the performance and interaction of the compo-nents under passing trains is a challenge.

From development of new rail sections to improv-ing the tie and fastening systems, technologicaladvances have made rail competitive as a trans-portation mode. Advances in track support and mea-surement systems are ensuring a more efficient andsafe performance from the track structure. Structuralmeasures evaluate the geometric smoothness andcondition of track and provide the data for assessingtrack performance.

The efficiency of track structure increases with

structural reliability brought about by improvedcomponents and by diagnostic tools that can identifyzones of increased failure risk. These tools, alongwith methods to improve track stability, are criticalto the competiveness of the U.S. rail industry.

Track diagnostic tools provide assessments of themost common failure modes. Each tool has devel-oped from an accident that exposed a particular vul-nerability of the track structure, indicated in thestatistics of the Federal Railroad Administration’s(FRA’s) Railway Accident–Incident Reporting Sys-tem.

Track components have been hardened andstrengthened to improve durability and performance,but increases in train loads and speeds, coupled with

Gaining Track Support to Improve TrackSafety, Efficiency, and theCompetitiveness of the Rail IndustryT E D S U S S M A N N , D A V I D R E A D , J O H N C H O R O S , A N D S H A N E M . F A R R I T O R

Railroads andResearch Sharing Track

Acela Express on theNortheast Corridor.

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recent extreme weather events, have necessitatedconstant vigilance for track safety. Reducing thestresses by ensuring proper performance of the trackstructure is a key endeavor. Track structure diagnos-tic tools can ensure that the track structure is work-ing to reduce the stress on individual componentsand can help avoid the stresses associated with thedeterioration of local track support.

Safe, Efficient InfrastructureSafety and efficiency are often competing goals—safety requires good track performance, but effi-ciency requires low-cost track maintenance andconstruction. The two goals must be addressedtogether successfully and positively to ensure indus-try competitiveness. The rail industry has accom-plished this—rail is the leading transportation modein terms of safety and efficiency.

The industry has developed and implementedtechnologies for safe operations, but at low initialcost in response to pressure from competitors andinvestors. Figure 1 (below) illustrates safety trends.Periodically the industry has applied a long-termperspective to the goal of keeping costs low and hasbuilt infrastructure that will last, realizing that thecost of replacement would be prohibitive.

The service life of railway track varies; many lineshave served for more than 100 years. The service lifeof track components, however, generally extendsinto tens of years. An increase in component life,therefore, will yield an economic benefit.

An economic analysis of the life cycle of trackinfrastructure should consider a period of more thanthe typical 20 years and take into account the vari-

ability of service life among components. This typeof analysis places a premium on maintenancethroughout the service life. The economic goalshould be a predictable track life cycle in which nosingle component fails or compromises the integrityof the whole.

Performance CharacteristicsOne of the challenges facing the industry is the ini-tial capital investment, which involves justifying theincreased initial costs to reduce life-cycle costs.Therefore a premium, next-generation track struc-ture is likeliest in a passenger corridor with strongridership and a tight operating schedule (1). Exceptin California, most planned U.S. passenger projectswill be incremental—new service will be established,

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Workers from New York’sMetropolitanTransportation Authorityrepair damage to Metro-North’s Hudson Line afterSuperstorm Sandy in2012. Extreme weatherand increases in trainloads and speeds requireconstant attention totrack safety.

865

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FIGURE 1 Track safety trends for the past 10 years show decreases in track-related derailments, whichnevertheless constitute 32 percent of rail accidents.

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and existing service will be improved, while majorinfrastructure additions are undertaken.

Premium track designs—for example, direct fix-ation concrete slab track instead of ballast (see pho-tograph, above)—may be used in critical locations,such as urban corridors, for which the primary con-cern is service reliability, as in large portions of theJapanese high-speed rail network. France’s high-speed rail network, in contrast, has relied on bal-lasted track (2),which is common on corridors withspeeds and traffic volumes similar to those of theemerging and high-speed corridors in the UnitedStates.

Required performance characteristics for high-performance ballasted track are as follows:

1. Premium track components;2. Good track support;3. Open, maintainable track structure;4. Realignment, repair, and maintenance flexibil-

ity; and5. Surveys of the track location.

Track constructed with these characteristics mustbe monitored periodically to assess condition, to planmaintenance, and to evaluate safety. The inspectionsshould apply measures of track structural conditionto identify any variations from the design at an earlystage, ensuring the effectiveness of repairs in achiev-ing the desired long-term performance.

Structural AssessmentA structural assessment measures engineering prop-erties or physical characteristics to assess the stabil-ity and durability of the track. Track geometryinspections, in contrast, focus on smoothness forride quality and on vehicle derailment risk. A trendof deterioration in track geometry may indicate com-promised structural integrity, but additional, appro-priate data are needed to diagnose the cause or toevaluate track load capacity or expected service life.A structural assessment of track applies parametersdirectly linked to failure mechanisms; it detectsemerging structural problems, evaluates stability anddurability, and enables timely repairs.

The parameters for track structural assessmentare linked to specific failure mechanisms and theassociated failure risks, as shown in Table 1 (above).A derailment caused by track buckle or misalign-ment will damage cars, equipment, and track exten-sively, but a wide-gage track geometry—when railsare spread wider apart, so that the wheelsets dropbetween the rails—may be less destructive and maycause less potential harm. The failure mechanismslisted in the table either have a high likelihood ofoccurrence—such as wide gage—or have the poten-tial to be particularly destructive—such as trackbuckle—and sometimes both.

Lateral Track SupportLateral track strength is the resistance of track to lat-eral movement. Passing traffic or built-up stress inthe rail generates lateral loads, which tend to deformthe track. Lateral track strength measurement

Transition from slab trackto ballasted track atdemonstration test,TransportationTechnology Center, Inc.

High-speed rail inFrance—a system thatshares features withhigh-speed rail in theUnited States—uses high-performance ballastedtrack.

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TABLE 1 Track Structural Parameters andFailure Mechanisms

Parameter Failure Mechanism

Lateral track strength Track buckle

Rail neutral temperature Rail pull-apart, track buckle

Gage restraint Wide gage, wheel drop, rail rollover

Ballast condition Track instability, geometry fault

Track deflection Track load capacity, settlement

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addresses tie displacement under a lateral forceapplied by a constant vertical load, as illustrated inFigure 2 (above). Lateral resistance can be evaluatedwith stationary tests or with moving loads, such asthe Association of American Railroads’ track loadingvehicle (TLV) (2, 3).

Lateral track strength decreases substantially aftertamping—a maintenance activity that raises the bal-last layer to correct the track profile; tamping pre-sents a particular risk to lateral track deformationuntil the track is stabilized, as illustrated in Figure 3(below) (2).

Longitudinal StabilityLongitudinal rail movement changes both the railstress condition and the temperature, increasing therisk that the track will buckle (3) or pull apart. Thetrack lateral resistance must be high enough to avoidbuckling; again, tamping may present a risk of buck-ling until the track is stabilized.

New rail stress measures are in development toaddress the effect of rail movement through the fas-tener, as well as to evaluate the track position, bothof which are challenging tasks. Various rail com-pression or tension measurements have emerged andhave been used in assessing rail stress, including theVortok Verse and a noncontact, ultrasonic devicepioneered by the University of California, San Diego,under the sponsorship of FRA.

Gage WideningTrack gage strength is measured by applying a lateralload to both rails under a constant vertical load andthen measuring the deflection. The strength isassessed based on the difference in track gage beforeand at the load application; the difference is known

FIGURE 2 Lateral track strength measurement.

20,000 lb vertical

Panel shift

0–40,000 lblateral

20,000 lb vertical

Lateral tiedisplace -mentmeasured

High strengthresponse has littleor no residualdisplacement

Low strength haslarge residualdisplacement

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Residualdisplacement

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Pre-TampPost-Tamp

FIGURE 3 Lateral track strength data recorded by atrack-loading vehicle before and after tracktamping.

Association of AmericanRailroads’ track-loadingvehicle.

Testing of University ofCalifornia–San Diego’srail neutral temperaturemeasurement device oncontinuous welded railwith concrete ties atTransportationTechnology Center, Inc.Note the strain gauge oneach side for validationand comparison.

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as delta gage. Rail-bound vehicles that operate onlyon track and high-rail vehicles that can operate onroad and track have been developed to measure gagestrength (4); examples include the TLV, the FRADOTX-218 gage restraint measurement system, andthe Holland Track Star.

Ballast ConditionBallast is the track’s foundation, and the ballast con-dition affects long-term performance of the track;any settlement-related degradation of performancewill cause stress on track components and rollingstock. As track degrades, ballast wear under load orfrom contamination with material blown in or spilledfrom passing trains can cause ballast fouling, whichcan increase the rate of deterioration (5).

Track inspections can detect ballast fouling withground-penetrating radar (GPR), a nondestructivetechnology that pulses electromagnetic energy intothe ground to develop an image of the subsurface (6,7), as shown in Figure 4 (below, left). Although themeasurement of fouling has been a challenge withGPR, methods have developed to analyze the differ-ence in signal response between clean ballast andhighly fouled ballast and to correlate the result withaccepted measures of fouling condition (8, 9). GPRalso may assist in measuring the layer thickness, pro-file, moisture content, and drainage of track sub-structure and may detect buried objects.

Track DeflectionTrack support is critical to track performance. Thebest measure of track support is the vertical trackstiffness, analyzed with the track vertical load-deflec-tion curve slope (9), as illustrated in Figure 5 (right).Most important are the slope associated with theseating deflection, which indicates gaps of slackbetween track components, and the slope associatedwith the contact deflection, which indicates the load-deflection response of the track when all elements areengaged. The contact deflection is associated withvariations in subgrade stiffness, track superstructure,and the shallow substructure.

Challenges to measuring the full load-deflectioncurve have led to the development of a system by theUniversity of Nebraska–Lincoln to survey the trackfor locations of excessive track deflection (10). A

beam mounted to the side frame of a truck measuresthe relative position of the wheel–rail contact and areference point on the rail 4 feet away. A high read-ing indicates a large deflection, which implies tracksupport problems.

Measuring deflection will become increasinglyimportant for maintenance planning, because exces-sive deflection increases stress in the rail, decreasingservice life (11, 12). Comprehensive testing of thecurve slope and of the measuring system developedby the University of Nebraska–Lincoln has shownthat deflection measurements complement othertrack measurements.

High ExpectationsThe rail industry anticipates growth in intermodaltraffic, both domestic and international, as publicentities and trucking companies turn to the railroadsto help solve problems of highway congestion, esca-lating fuel prices, and driver shortages. Challengesinclude issues associated with an aging infrastructureand an aging workforce, along with a constant pres-sure to maintain leadership in terms of safety andefficiency. The pressure to do more with fewerresources and less staff has never been greater.

Track structural assessment and inspection toolspresent unique opportunities to respond to thesechallenges. By providing timely and accurate safetyinspections, by guiding maintenance, and by ensur-ing efficient use of resources, these technologies canadvance the efficiency and safety goals of the indus-try. In addition, these technologies can assist in eval-uating compliance with construction specifications,so that new rail infrastructure can offer higher levelsof quality and uniformity.

The vibrant history of railway track research anddevelopment has introduced many technologies thathave spurred further understanding of track behav-ior and quality. Industry has applied these advancesto the training of inspectors and workmen in thefiner points of track behavior and inspection.

These efforts have produced high expectations

FRA DOTX-218 gagerestraint measurementsystem with University ofNebraska–Lincoln’s trackdeflection system.

Radar

FIGURE 4 Ground-pen etrating radar signalgeneration in responseto track substructureboundaries.

Coarseaggregate

ballast layerWell-graded gravel

subballast layer

Fine grain subgrade soil

Air

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Vertical Rail Deflection (in.)

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Maximum deflection

Seating deflection

Contact deflection

FIGURE 5 Track vertical load-deflection curve slope.

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for industry safety and efficiency. Continuing thistrend will require research targeted at persistent andunrelenting safety risks. Building higher-qualityinfrastructure and using structural inspection toolsto monitor deterioration will ensure that the indus-try can meet the ever-increasing safety and cost effi-ciency expectations of modern railway track.

References1. Li, D., Bilow, D., and T. R. Sussmann. Slab Track for Shared

Freight and High-Speed Passenger Service. Proceedings ofthe 2010 Joint Rail Conference on High-Speed and IntercityRail, Urbana, Illinois, April 2010.

2. Esveld, C. Recent Developments in High-Speed Track. Pro-ceedings of the First International Conference on Road and RailInfrastructure, Opatija, Croatia. May 17–18, 2010.

3. Sussmann, T. R., A. Kish, and M. J. Trosino. Investigation ofthe Influence of Track Maintenance on the Lateral Resistanceof Concrete Tie Track. In Transportation Research Record:Journal of the Transportation Research Board, No. 1825, Trans-portation Research Board of the National Academies, Wash-ington, D.C., 2003, pp. 56–63.

4. Li, D., R. Thompson, P. Marquez, and S. Kalay. Developmentand Implementation of a Continuous Track-Support TestingTechnique. In Transportation Research Record: Journal of theTransportation Research Board, No. 1863, TransportationResearch Board of the National Academies, Washington,D.C., 2004, pp. 68–73.

5. Sussmann, T. R., M. Ruel, and S. Chrismer. Source of BallastFouling and Influence Considerations for Condition Assess-ment Criteria. In Transportation Research Record: Journal ofthe Transportation Research Board, No. 2289, TransportationResearch Board of the National Academies, Washington,D.C., 2012, pp. 87–94.

6. Choros, J., T. R. Sussmann, M. Fateh, and E. Curtis. GageRestraint Measurement System Comparison Tests: Railboundand Hi-Rail Vehicles. Report No. DOT/FRA/ORD/03/29. Fed-eral Railroad Administration, 2003.

7. Roberts, R., I. Al-Qadi, E. Tutumluer, J. Boyle, and T. Suss-mann. Advances in Railroad Ballast Evaluation Using 2 GHzHorn Antennas. Presented at 11th International Conferenceon Ground-Penetrating Radar, Columbus, Ohio, 2006.

8. Roberts, R., I. Al-Qadi, E. Tutumluer, and J. Boyle. Subsur-face Evaluation of Railway Track Using Ground-PenetratingRadar. Report No. FRA/ORD-09/08. Federal RailroadAdministration, 2008.

9. Silvast, M., M. Levomaki, A. Nurmikolu, and J. Noukka.NDT Techniques in Railway Structure Analysis. Presented at7th World Congress on Railway Research, Montreal, Canada,June 2006.

10. Sussmann, T. R., W. E. Ebersohn, and E. T. Selig. Funda-mental Nonlinear Track Load-Deflection Behavior for Con-

dition Evaluation, In Transportation Research Record: Journalof the Transportation Research Board, No. 1742, TRB, NationalResearch Council, Washington, D.C., 2001, pp. 61–67.

11. Farritor, S. Real-Time Measurement of Track Modulus from aMoving Car. Report No. FRA/ORD-05/05. Federal RailroadAdminstration, December 2005.

12. Greisen, C., S. Lu, H. Duan, S. Farritor, R. Arnold, T. Suss-mann, W. GeMeiner, D. Clark, T. Toth, K. Hicks, M. Fateh,and G. Carr. Estimation of Rail Stress from Real-Time Verti-cal Track Deflection Measurement. Presented at AmericanSociety of Mechanical Engineers Joint Rail Conference,Pueblo, Colorado, March 2009.

State-of-the-art trackassessment vehicles nearCheyenne, Wyoming:Union Pacific EC-4evaluation car and FRADOTX-218 gage restraintmeasurement system inconsist with University ofNebraska–Lincoln trackdeflection system.

IDEA Programs Seek Proposals for Railroad Safety

T he Transportation Research Board (TRB) is accepting proposals for proj-ects to develop and test innovative methods to improve railroad safe-

ty or performance through the Safety Innovations Deserving ExploratoryAnalysis (IDEA) Program. Proposals should seek to develop or test promis-ing but unproved innovations to advance railroad practice and can be ap-plicable to any type of railroad, including high-speed rail, intercity passen-ger rail, or freight railroads.

Proposals are due September 16, 2013. The Federal Railroad Adminis-tration (FRA) funds the Safety IDEA program, which is managed by TRB.

For instructions on preparing and submitting IDEA proposals, see theIDEA Program Announcement on the IDEA website, www.TRB.org/IDEA.Proposals are eligible for up to $100,000 in IDEA funds. Address questionsto Jon Williams, jwilliams@nas.edu, 202-334-3245.

Installation of an IDEA projectat the Trans -portationTechnologyCenter, Inc., todetect railroadcar truckhunting, orswaying.

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