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Barkan is Professor ofCivil and EnvironmentalEngineering and Execu-tive Director of the RailTransportation and Engi-neering Center (Rail-TEC), University of Illinois at Urbana–Champaign. Liu is Assis-tant Professor of Civiland Environmental Engi-neering, Rutgers Univer-sity. Saat is Research Assistant Professor inRailway Engineering, Department of Civil andEnvironmental Engineer-ing and RailTEC, University of Illinois at Urbana–Champaign.

The nation’s quest for energy self-sufficiencyhas led to a dramatic increase in the transportof flammable liquids by rail. In the first

decade of the 21st century, the rail transport of alco-hols not otherwise specified (NOS) increased 10-fold from approximately 30,000 tank carloads peryear to more than 300,000 in 2010. As the alcoholtraffic stabilized, an even more dramatic increase inthe transport of petroleum crude oil began with theboom in shale oil production.

Rail transport of petroleum crude oil increasedmore than 50-fold from approximately 9,500 carloadsin 2008 to 500,000 in 2014, with further growthexpected (1). Railroad safety improved in the sameperiod, declining from 4.39 accidents per million trainmiles in 2004 to approximately 2.25 in 2014, a 49 per-cent reduction (Figure 1, below) and the lowest levelsince the Federal Railroad Administration (FRA)began recording these statistics in 1975.

ProblemDespite the reduction in the accident rate, the sub-stantial growth in flammable liquid traffic raised con-cern about the risk of accidents producing largespills. The new traffic was moving differently, oftenin unit trains of 80 to 120 cars from origin to desti-nation. Damage to conventional, nonjacketed DOT-111 tank cars, combined with thermally causedfailures in large, multiple tank car derailments,resulted in several dramatic—and two fatal—trainaccidents.

The accidents galvanized industry, public, and gov-

ernment attention on the topic. The rail industry faceda paradoxical situation: train safety was improving, butthe risk was increasing with the dramatic growth intraffic.

SolutionImproving the safety and reducing the risk involvethree key elements:

u Railroad accident prevention,u Improved tank car safety design, andu Enhanced emergency response capabilities.

The research on tank car safety design—the focusof this article—was a collaborative, multiyear effort byseveral organizations, including the Railway SupplyInstitute (RSI)–Association of American Railroads(AAR) Railroad Tank Car Safety Research and TestProject, the U.S. Department of Transportation (DOT)FRA, the U.S. DOT National University Rail Center,the Rail Transportation and Engineering Center (Rail-TEC) at the University of Illinois at Urbana–Cham-paign (UIUC), and several other individuals andcompanies (2).

Safety-Related QuestionsThe research started by addressing two questions:

u How effectively do different tank car safetydesign features prevent releases?

u What is the optimal combination of design fea-tures?

Enhanced Tank Car Design Improves the Safety ofTransporting Crude Oil and Alcohol by RailC H R I S T O P H E R P. L . B A R K A N , X I A N G L I U , A N D M . R A P I K S A A T

R E S EARCH PAYS O F F

FIGURE 1 Reportable trainaccidents per million trainmiles (green) and growth inrailroad tank car shipments ofalcohol NOS (blue) andpetroleum crude oil (orange)in the United States,2004–2014. [Sources: Foraccident data: FederalRailroad Administration:http://safetydata.fra.dot.gov/officeofsafety/publicsite/summary.aspx (2014 data arepreliminary); for traffic data:Association of AmericanRailroads.]

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02004 2006 2008 2010 2012 2014

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The RSI-AAR Tank Car Safety Project analyzeddata on tank car safety performance (3), quantifyingthe effect of different tank car design features on thelikelihood of a release in accidents (4). Researchers atUIUC then used these statistics and other data todevelop an optimization model for a tank car safetydesign (5). The researchers quantified the safety ben-efit of each design change element, along with its asso-ciated impact on tank car weight, to determine whichcombinations of design enhancements were mosteffective and efficient.

The changing nature of rail traffic, however, withincreased movement by unit trains, raised new safety-related questions:

u Do unit trains derail at a rate different from thatof conventional trains?

u What is the likelihood of large, multiple carreleases?

u What was the effect of fire on tank car failures?

UIUC developed an integrated risk model for haz-ardous materials transportation to evaluate railroadinfrastructure, operating practices, tank car design,and routing and to investigate the most efficient com-bination of measures to reduce risk (6). A preliminaryanalysis suggested that the derailment rate for unit

trains was not significantly different from that of othertypes of freight trains. Research on this topic is con-tinuing, but given the declining accident rate, the mostplausible explanation for the increased number of inci-dents is the dramatic increase in unit train traffic.

Multiple Car AccidentsThe RSI-AAR data enabled a statistical estimate of howeach particular tank car design would perform in acci-dents (Figure 2, left); however, the substantial increasein unit train traffic led to concern about the occurrenceof large, multiple-car release accidents. UIUC thereforeused a new risk model to estimate the probability ofrelease events of various magnitudes for different tankcar designs.

The findings indicated that even relatively smalldifferences in the probability of individual car releasesyielded large differences in the probability of multiplecar releases (7). For example, a design improvementthat resulted in a 20 percent reduction in release prob-ability for a single derailed car offered a 74 percentreduction in the probability that five or more derailedcars would release.

The risk model was used to calculate how the dif-ferent tank car designs affected the relative expectedtime intervals between events of various magnitudes(Figure 3, below left). The most important findingwas that even small differences in an individual car’sprobability of release diverged geometrically when theprobability of larger numbers of cars releasing wascalculated (compare Figure 2 with Figure 3). Thisresult was influential in the industry’s decision to sup-port a more robust tank car design.

Protection from FiresAlthough the improved damage resistance reducedthe incidence of cars failing from the initial, physicalimpacts of a derailment, another aspect of unit trainderailments emerged and gained importance. Even ifonly a few cars release their contents, a fire may ensue.

The fire can engulf other derailed tank cars that hadnot released in the initial derailment. The productinside the cars would heat up, increasing the pressureinside the tank, while the fire impinging on the tankwould thin and weaken the steel on the upper side,reducing its strength. If the rising internal pressureexceeds the strength of the weakening tank, a separa-tion—known as a thermal tear—could occur in thetank steel, and a large quantity of product would sud-denly release, triggering the vertically directed fire-balls sometimes seen in these incidents.

Industry and government had sponsored the devel-opment of a research tool known as Analysis of FireEffects on Tank Cars (AFFTAC) to evaluate increasesin thermally induced pressure and the effectiveness of

FIGURE 2 Percentage oftank cars of variousdesigns expected torelease 100 or moregallons (CPR100) fromphysical impacts in FRA-reportable accidents (4).

FIGURE 3 Illustration ofthe effect of tank cardesign on the geometricdivergence of theexpected intervalbetween occurrences ofmultiple car releaseincidents of varyingmagnitude.

Percent Releasing

20

15

10

5

0ConventionalNonjacketedDOT-111

Time Interval Between

Multiple-Car Releases

Minimum Number of Cars Releasing

1 2 3 4 5 6 7 8 9 10

ConventionalJacketed DOT-111

Jacketed 9/16" (DOT/TC-117)

Jacketed 1/2"

Jacketed 7/16" CPC-1232

Conventional Jacketed DOT-111

Nonjacketed 1/2" CPC 1232Conventional Nonjacketed DOT-111

Nonjacketed1/2"

CPC-1232

Jacketed7/16"

CPC-1232

Jacketed1/2"

Jacketed9/16"

DOT/TC-117

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designs for pressure relief devices (8). The industryused AFFTAC to develop a thermal protection systemto extend the survivability of petroleum crude oil andalcohol NOS tank cars in fires as long as possible, ide-ally preventing the tank cars from failing altogether.

Researchers identified a twofold solution:

u First, place a layer of thermal insulation aroundthe tank and encase the insulation in a steel jacket toreduce the rate of heat flux into the tank and toimprove resistance to damage in derailments—in Fig-ure 2, for example, compare the jacketed with thenonjacketed versions of the conventional DOT-111.

u Second, equip cars with appropriately sizedpressure-relief valves to reduce internal pressure moreeffectively in a controlled manner.

BenefitsThe research described here was used to inform thedevelopment of the enhanced tank car safety designfeatures proposed by the rail industry for transportingpetroleum and alcohol NOS:

u A thicker, more puncture-resistant tank con-structed of stronger steel;

u Full-height head shields;u Robust top-fittings protection; andu A thermal protection system encased in a steel

jacket (Figure 4, above) (9).

This tank car is expected to reduce the averageprobability of a release caused by the impacts of anaccident by an estimated 85 percent compared withthe probability of a release by the current nonjacketedDOT-111 car; moreover, the enhanced design isexpected to reduce considerably the likelihood of sec-ondary failures caused by fire.

U.S. DOT and Transport Canada recently promul-gated regulations to incorporate these features intothe new DOT-TC-117 tank car (10, 11). When fullyimplemented, these cars will improve substantially

the safety of transporting petroleum crude oil andalcohol NOS by rail in the United States and Canada.

References1. Moving Crude Oil by Rail. Association of American Rail-

roads, Washington, D.C., 2014. 2. Barkan, C. P. L., M. R. Saat, F. González III, and T. T. Treichel.

Cooperative Research in Tank Car Safety Design, TR News,No. 286, May–June 2013, pp. 12–19.

3. Daum, P. J. Energy Transportation Safety on the Rails: His-torical View. TR News, No. 298, June–July–August 2015, pp.38–40.

4 . Treichel, T. T. RSI-AAR Tank Car Accident Safety Researchfor Crude Oil and Ethanol Cars. Presented at NationalTransportation Safety Board Forum on Transportation ofCrude Oil and Ethanol, April 22–23, 2014. Washington,D.C. www.ntsb.gov/news/events/Documents/Panel%201_C_Todd%20Treichel.pdf.

5. Saat, M. R., and C. P. L. Barkan. Generalized Railway TankCar Safety Design Optimization for Hazardous MaterialsTransport: Addressing the Trade-Off Between Transporta-tion Efficiency and Safety. Journal of Hazardous MaterialsNo. 189, 2014, pp. 62–68.

6. Liu, X., M. R. Saat, and C. P. L. Barkan. Integrated RiskReduction Framework to Improve Railway HazardousMaterials Transportation Safety. Journal of Hazardous Mate-rials, No. 260, 2013, pp. 131–140.

7. Liu, X., M. R. Saat, and C. P. L. Barkan. Probability Analy-sis of Multiple Tank Car Release Incidents in Railway Haz-ardous Materials Transportation. Journal of HazardousMaterials, No. 276, 2014, pp. 442–451.

8. Runnels, S. AFFTAC Analysis of Fire Effects on Tank Cars.RSI-AAR Railroad Tank Car Safety Research and Test Proj-ect, 2013. www.srconsult.com/AFFTAC_UsersManual_4_00_Beta_06.pdf.

9. Tank Car Standard: Future Tank Car. Railway Supply Insti-tute, Washington, D.C. www.tankcarresourcecenter.com/wp-content/uploads/2014/07/Tank-Car-Handout1.pdf.Accessed April 22, 2015.

10. Regulations Amending the Transportation of DangerousGoods Regulations (TC-117 Tank Cars). Transport Canada,Ottawa, Ontario. www.tc.gc.ca/media/documents/tdg-eng/AmendmentEng.pdf. Accessed May 7, 2015.

11. Final Rule: Hazardous Materials: Enhanced Tank Car Standardsand Operational Controls for High-Hazard Flammable Trains.Pipeline and Hazardous Materials Ad min istration, U.S. De-partment of Transportation, Washington, D.C. www.fra.dot.gov/eLib/Details/L16354. Accessed May 7, 2015.

Suggestions forResearch Pays Off topicsare welcome. ContactG. P. Jayaprakash,Transportation ResearchBoard, Keck 488, 500Fifth Street, NW, Washington, DC 20001(202-334-2956;gjayaprakash@nas.edu).

FIGURE 4 Illustration of thenew safety features on tankcars for transportingpetroleum crude oil andalcohol NOS. (Drawingcourtesy of Railway SupplyInstitute)

EDITOR’S NOTE: Apprecia-tion is expressed to G. P.Jayaprakash and AmirHanna, TransportationResearch Board, for theirefforts in developing thisarticle.