Advanced Tank Car Collaborative Research Program 

(ATCCRP) 

Executive Summary and Conclusions 

December 2016

Report Submitted to: 

American Chemistry Council 

Association of American Railroads 

The Chlorine Institute 

The Fertilizer Institute 

Railway Supply Institute 

Transport Canada 

U.S. Department of Transportation - Federal Railroad Administration 

U.S. Department of Homeland Security - Transportation Security Administration 

 

 

 

Advanced Tank Car Collaborative Research 

Program Executive Committee 
 1 

Executive Summary and Conclusions 

Over the last decade, there has been significant ongoing research to develop strategies for 

improving railroad tank cars so they can maintain tank integrity for more severe accident 

conditions. Beginning in 2006 and continuing through 2009, Dow Chemical Company, Union 

Pacific Railroad, and Union Tank Car Company assembled a joint project team to drive forward 

a holistic process for the development of a next generation rail tank car. This work was 

performed under the Next Generation Railroad Tank Car (NGRTC) Program and completed in 

cooperation with U.S. Department of Transportation, Federal Railroad Administration (DOT – 

FRA), Transport Canada (TC), and U.S. Department of Homeland Security Transportation 

Security Administration (DHS - TSA) and addressed safety, security, emergency response and 

operational challenges. The NGRTC program developed a database of both full-scale impact 

testing on tank cars and tank heads as well as a significant database on characterization of tank 

car materials and laboratory scale component tests (e.g. panel punch tests). An additional effort 

in the NGRTC Program was the development and validation of detailed finite element tank 

impact models and tank car steel constitutive and failure models which can be used to accurately 

predict the puncture resistance under different impact conditions [1]. 

Subsequent to the NGRTC Program, the Advanced Tank Car Collaborative Research Program 

(ATCCRP) was initiated to coordinate research efforts to enhance the safety and security of rail 

tank car shipments of toxic inhalation hazard (TIH) materials. The ATCCRP builds on the prior 

and ongoing research conducted by the NGRTC Project, the Chlorine Institute (CI) tank car 

safety research [2-4], and the RSI-AAR Tank Car Safety Research and Test Project [5, 6]. The 

ATCCRP is a joint effort comprised of the following groups: shippers of tank cars carrying toxic 

inhalation hazard (TIH) materials [represented by the American Chemistry Council (ACC), CI, 

and the Fertilizer Institute (TFI)]; railroads that transport hazardous materials [represented by the 

Association of American Railroads (AAR)]; and rail tank car builders and lessors [represented 

by the Railway Supply Institute (RSI)]. In addition, Memoranda of Cooperation (MOC) were 

developed to formalize cooperation agreements between ATCCRP participants and the DOT - 

FRA, TC, DHS - TSA and the DHS Science and Technology Directorate (DHS - S&T). 

Some of the significant conclusions resulting from the ATCCRP and supporting tank car safety 

research efforts are: 

1. We have vastly improved our understanding of tank impact and puncture behaviors and 

developed a wealth of new experimental data and analytical results to support ongoing 

and future tank car safety efforts. 

2. No new high technology design or material that produced significant new protection 

levels (e.g. composites, crushable foams, advanced engineered energy absorbing 
Advanced Tank Car Collaborative Research Program Executive Summary and Conclusions December 2016 

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sandwich panels) has been identified. Traditional tank car designs with monolithic 

layers of good quality steel are relatively efficient structures for resisting the impact 

threats in the railroad safety environment. 

3. The HM-246 interim specification cars provide a significant level of improvement over 

the legacy designs. The HM-246 interim specification car puncture energy 

improvements were on average 90%, 100%, and 45% for the anhydrous ammonia (AA), 

ethylene oxide (EO), and chlorine (Cl) cars respectively. Empirically-derived 

probabilities of lading release for interim specification cars were 51% to 61% lower than 

those of legacy cars. 

4. The only option identified for possible improvements in puncture protection over the 

HM-246 interim specification car designs are potential optimized sandwich designs, 

requiring alternative steels in the jacket (outer tank) for enhanced puncture 

protection. This conclusion is based on puncture analyses performed for various tank 

design configurations. Functional tank car designs for these sandwich cars were not 

developed in the research and the protection levels have not been proven by testing. 

1.1 Background 

An objective at the beginning of the Next Generation Rail Tank Car (NGRTC) program (2006-

2009) was to develop, if possible, an advanced tank car design that could withstand 5-10 times 

higher impact energies than the baseline designs. To achieve this, the NGRTC program 

investigated both the puncture behavior of existing tank car designs and advanced tank car 

protection concepts. These advanced concepts included crushable structures and energy 

absorbing concepts developed for various applications (e.g. automotive, ship structures, 

aerospace). Example concepts included multi-layer sandwich structures with crushable foams or 

engineered metal cores. Although these advanced systems were shown to have potential for 

large area blunt impact loads, they performed poorly for smaller impactors (e.g. a broken rail) 

that could sequentially puncture the layers and prevent the system from resisting significant 

impact force or dissipate significant energy. As a result, an outcome of the NGRTC program 

was that systems that primarily relied on one or two larger monolithic layers that can 

independently (or collaboratively) resist significant forces for small impactors were considered 

to be the most promising designs. Traditional tank car designs were found to be relatively 

efficient for resisting impacts and punctures for a given structural weight. The NGRTC program 

also concluded that the goal of a 5-10 times increase impact energy was probably not achievable 

with any realistic tank design. 
Advanced Tank Car Collaborative Research Program Executive Summary and Conclusions December 2016 

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The Advanced Tank Car Collaborative Research Program has a similar purpose and scope: to 

further improve the safety and security of rail tank cars carrying TIH materials. The ATCCRP 

was organized by first collecting a wide range of technical white papers (TWP) on potential 

technologies that could improve the safety and security of tank cars. These topics included the 

following (note: some numbers are missing because similar topics were combined): 

TWP-1: Effect of Pressure on Puncture Resistance – Chlorine and Anhydrous Ammonia 

TWP-3: Reducing Dispersion Effects by Lading Temperature Reduction 

TWP-4: Sandwich Tank Car Design 

TWP-5: Composite Materials for Protection Systems 

TWP-6: Structural Foams and Adhesives 

TWP-9: Coupler Modifications 

TWP-10: Correlating Material Properties to Puncture Resistance 

TWP-11: Relating Conditional-Probability-of-Release to Modeling and Tests 

TWP-13: Other TIH Materials 

TWP-14: Analysis of Different Impactor Threats and Impact Conditions 

TWP-15: Development of Performance-Based Testing Requirements for Railroad Tank Cars 

TWP-16: Application Study for Perforated Armor Plating 

TWP-17: Revising and Updating Conditional Release Probability Estimates 

TWP-18: Forensic Analyses and Elimination of Real-World Failures 

TWP-19: Improvements in Tank Car Weld Safety 

TWP-20: Investigation of Impactors in Past Accidents 

TWP-21: Demonstrate Approval Protocols on Candidate Technologies 

TWP-22: Development of Advanced Head Protection Concepts 

Note that the initial topics through TWP-14 were developed at the start of the ATCCRP efforts 

and additional TWPs were added at later times as they were identified and proposed. 

The ATCCRP participant organizations reviewed and ranked the merits of the TWPs including 

anticipated commercial feasibility; estimated costs; and proposed schedules. Each organization 

identified the five TWP projects they believed were most important and likely to provide 

meaningful results. A system was worked out and used to identify inter-dependencies between 

projects and rate the proposed TWP research against the following ATCCRP objectives: 
Advanced Tank Car Collaborative Research Program Executive Summary and Conclusions December 2016 

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 Improved puncture resistance; 

 Reduce releases at top fittings; 

 Mitigate potential security threats; 

 Provide a basis for possible use in establishing regulatory standards and protocols for 

performance tests; 

 Enhance security, situational awareness, and tools for emergency responders. 

The ATCCRP Committee decided to perform the following projects:

 TWP-14 (Analysis of Different Impactor Threats and Impact Conditions) 

 TWP-11 (Relating Conditional Probability of Release to Modeling and Tests) was 

initiated as a smaller Phase I proof of concept effort. 

 TWP-17 (Update and Expansion of Report RA-05-02 on Lading Loss Probabilities) 

as a predecessor to the TWP-11 effort. 

 TWP-10 (Correlating Material Properties to Puncture Resistance)

 TWP-5 (Composite Materials for Protection Systems) Phase I modeling effort was 

initiated as a proof of concept. 

 TWP-4 (Sandwich Car Design) 

 TWP-15 (Development of Performance-Based Testing Requirements for Railroad 

Tank Cars) was performed as an initial effort where impact tests were performed 

under FRA sponsorship to establish the baseline side impact response of DOT-111 

and DOT-112 tank cars. 

 TWP-22 (Development of Advanced Head Protection Concepts) 

1.2 Summaries of the ATCCRP Projects 

More detailed summaries of the findings leading to the conclusions given above are provided 

below. 

TWP-14 - Analysis of Different Impactor Threats and Impact Conditions 

The TWP-14 project was important since the NGRTC program had used a primary impactor 

threat of a 6x6 inch square punch with a 1⁄2 inch radius around the edges of the impact face. This 

impactor was chosen at the time to balance the design between concepts that work for energy 

dissipation in blunt object impacts and protection systems that resist penetration of sharp or small 

puncture threats. However, the distribution of the effective sizes of impactors and the size of the 

most critical impactor leading to punctures in real world derailments and accidents is not known. 
Advanced Tank Car Collaborative Research Program Executive Summary and Conclusions December 2016 

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Analyses of different impactor sizes and impact conditions were needed to improve the 

understanding of how the idealized conditions previously analyzed relate to the chaotic impact 

conditions and wide range of potential impactors that exist in derailments. 

The approach used in the research and development program was to apply a tank impact and 

puncture prediction capability using detailed finite element analyses (FEA). The FEA capability 

was developed and validated previously in the NGRTC program. In this study, the analyses 

were applied to investigate the tank puncture behaviors for a wide range of impact conditions. In 

the initial phase of this program, different sizes and shapes of impactors were investigated. The 

impactors used included square, rectangular, and round impact face geometries. A new 

parameter was developed to characterize the effective size of the impactor. This impactor 

characteristic size is the square root of the area of the impactor face. The impactor characteristic 

size parameter provided a good correlation for the different impactor sizes and shapes analyzed 

with a strong linear correlation of the puncture force with the characteristic size of the impactor. 

To investigate the effects of the impactor orientation, a series of analyses was performed with a 

12x12 inch square impactor with a 0.1-inch edge radius. The analyses were performed with 

various levels of pitch, yaw, and combined rotations to produce increasingly concentrated 

loadings along the impactor edges or corner. The analyses showed that the rotated orientations 

reduced the puncture forces from that of the 12-inch characteristic size to that of approximately a 

4.5-to5 inch effective characteristic impactor size when rotated to a 45-degree edge impact and 

as small as a 3-inch impactor for the corner impact. Corresponding analyses where the tank was 

rotated to produce oblique impacts produced similar reductions in puncture forces and puncture 

energies. As a result, we see that a large blunt impactor can have the puncture potential of a 

much smaller impactor when impacting under non-ideal (offset, oblique, or rotated) impact 

conditions. 

An additional result of the TWP-14 project was to characterize the puncture resistance of various 

tank designs for a wide range of impact conditions. In addition to the analyses performed on the 

baseline 105J500W chlorine (Cl) tank car, a series of other tank car types were analyzed. The 

evaluations were performed for the 105J600I Cl tank car (HM-246 interim specification car), the 

112J340W and 112J500I anhydrous ammonia (AA) tank cars, and 105J300W, 105J400W, and 

105J500I ethylene oxide (EO) tank cars. A full set of normal and 45-degree oblique side impacts 

were performed with a range of different size and shape impactors for each of the Cl, EO, and 

AA tank car designs considered. For comparison of the various designs, the calculated puncture 

energies all of the various designs were normalized to those of the 105J500W Cl tank car. The 

comparison for these normalized results is provided in Figure 1. 
Advanced Tank Car Collaborative Research Program Executive Summary and Conclusions December 2016 

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Figure 1. Comparison of relative puncture performance of various tank designs. 

In this comparison, the puncture energies for the 105J500W EO tank car design are considerably 

higher than for any of the other tank car design. The EO tanks have relatively high puncture 

energies as a result of the lower tank pressures and larger diameter tanks. The 105J500W, 

105J400W, and 105J300W EO tank cars have puncture energies on average 82% higher, 17% 

higher, and 12% lower, respectively, than the 105J500W Cl tank car. The puncture energies for 

the 105J600W Cl tank car were on average 37% higher than the 105J500W Cl tank car. The 

112J500W and 112J340W AA tank cars are on average 10% above and 39% below the 

105J500W Cl tank car, respectively. 

TWP-10 - Correlating Material Properties to Puncture Resistance 

The TWP-10 project was performed to assess a range of alternate tank car materials that could 

possibly improve puncture resistance. It built on the past material characterization efforts of the 

NGRTC Project (e.g. A1011, A516-70), and the Chlorine Institute sponsored program to 

characterize other high strength low alloy (HSLA) candidate steel materials (A710, HPS-70, and 

HPS-100). In the TWP-10 project, this past data is combined with additional testing and analysis 

to evaluate the impact and puncture resistance performance of candidate materials that could be 

used in tank car structure (both shell and jacket). The objective is that, by understanding the 

appropriate form of models for material damage and failure, analysts can predict structural 

performance and link the failure behavior to basic material properties. Such well-founded 
Advanced Tank Car Collaborative Research Program Executive Summary and Conclusions December 2016 

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modeling will allow design optimization and selection of the most appropriate material for the 

tank structures. 

The research program included detailed characterizations of various steel material samples 

(including a number of different TC128B variants). These detailed material characterizations 

included assessing tensile stress-strain properties as well as mechanical behavior of notched 

samples. As part of the research, detailed constitutive and damage models were developed for 

each material and the models were used to simulate the corresponding tests. 

In addition to the direct material characterization, a series of puncture analyses were performed 

for various candidate materials to identify the material characteristics that most strongly control 

puncture resistance. Candidate materials with a wide range of mechanical properties were used 

in a suite of puncture analyses under various side impact conditions using a Cl tank car geometry 

(following the TWP-14 methodology). This effort used a set of candidate steels with 

significantly different properties from TC128B as shown in Figure 2. Note that these candidate 

steels were selected based on their mechanical properties and availability of test data and not 

necessarily for their suitability for use in railroad tank car service (e.g. weldability, fatigue 

resistance, cost). The idea is that once the desirable mechanical properties were identified, the 

selection of a tank car material that optimizes the desirable properties could be identified. 

Figure 2. Candidate tank car steels with a range of mechanical properties. 
Advanced Tank Car Collaborative Research Program Executive Summary and Conclusions December 2016 

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The summaries of the normalized puncture energies for the impact analyses performed on the 

candidate steels are summarized in Figure 3. The 304L stainless produces the highest average 

normalized puncture energy (55% improvement over TC128B) but only a 17% improvement in 

average normalized puncture force which is less than three other materials (HY-100, A709 

HPS100, and HY-130). 

Figure 3. Relative puncture energy performance for candidate tank car steels. 

The material properties were investigated in different combinations in an attempt to understand 

the material characteristics that contribute most significantly to the puncture resistance. The goal 

was to relate puncture behavior (as determined from the full-scale numerical simulations) to the 

stress-strain properties of the materials (strength and ductility). Three models are proposed in 

this work that included linear combinations of ultimate strength, yield strength and ductility. All 

three models provide excellent predictions of the observed puncture behavior (within 10% of the 

TC128B-normalized puncture energy). The proposed models were determined empirically by 

least square fitting of the puncture data when combined with the different input variables. The 

resulting models provide a basis to predict the effect of differing strength properties of other 

candidate materials on the puncture behavior of a rail tank car. However, material selection is 

not simply based upon stress-strain curve properties. There are other issues involved (such as 

weldability, corrosion and fatigue resistance, toughness, material cost etc.) that clearly are not 

captured by these models. 
Advanced Tank Car Collaborative Research Program Executive Summary and Conclusions December 2016 

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Although these models are purely empirical, an examination of the numerical puncture force 

response clearly indicates the compelling role of the ultimate strength of the material in 

predicting puncture force levels. In addition, the force-deflection characteristics of the 

simulations exhibit reasonable correlation to the yield strength of the material. The trends 

observed indicate that an increase in ultimate strength leads to higher puncture energy; 

conversely, an increase in yield strength leads to a lower puncture energy. Thus a material that 

has a relatively low yield and high ultimate strength is most efficient at resisting punctures (e.g. 

304L stainless steel). Note that these results for the stainless steel were based on simpler 

constitutive models developed from tensile test data only. A more detailed material 

characterization of the stainless steel is ongoing. 

These material puncture models provide a viable method to compare and contrast different 

candidate materials for tank car structure. Without this tool, expensive and time-consuming 

laboratory tests and full-scale simulations would be required to evaluate different candidate 

materials. Moreover these models can be used to help the industry determine the possible impact 

of different material modifications that impact mechanical properties. Given these tools, 

puncture enhancement of different candidate materials can be predicted to aid in material 

selection decisions and cost-benefit analyses. Applying these models to various proposed 

candidate tank car steels indicate that most new materials will net at best a modest improvement 

in puncture performance. 

TWP-5 - Composite Materials for Protection Systems 

The TWP-5 project was performed as a Phase I modeling effort as a proof of concept. In the 

project, the *MAT_COMPOSITE_MSC_DMG model [7] was calibrated for an S-2 Glass fiber 

composite and puncture analyses were performed on a few tank car concepts to assess the 

potential performance of composite systems. The S-2 glass system was selected both based on 

the availability of the test data and having a good balance of properties (cost, availability, 

puncture resistance) for tank car application. The composite damage model was selected as the 

only available model that has all of the damage mechanics necessary for the dynamic puncture 

analysis of thick composite systems (delamination, punch shear mechanisms through thickness, 

etc.). 

The validation of the damage model was performed using punch data on S-2 glass/epoxy 

available in the open literature [e.g., 10-13] as shown in Figure 4. These are laboratory-scale 

tests of different panel thicknesses. The resulting model was applied to tank impact simulations. 

An example simulation is shown in Figure 5 where equivalent weight composite and steel jackets 

were evaluated. In this case, a 0.386-inch-thick TC128B steel jacket is compared to a 1.44-inchthick S-2 glass composite jacket. Although the composite is much thicker and has high strength, 
Advanced Tank Car Collaborative Research Program Executive Summary and Conclusions December 2016 

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the relative stiff elastic response results in the jacket reaching the failure point early in the 

deformation process (shown in Figure 5a). As a result, it did not appear that the composite 

systems could provide significant puncture protection performance improvements for the types 

of impact threats commonly experienced in tank car impacts and derailments. 

(a) Model of the panel punch test configuration 

(b) Model and test correlation 

Figure 4. Composite damage model validation for the panel punch tests. 
Advanced Tank Car Collaborative Research Program Executive Summary and Conclusions December 2016 

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(a) Calculated deflections at composite jacket failure 

(b) Comparison of the composite and steel jacket behaviors 

Figure 5. Calculated performance of equivalent weight steel and composite jackets. 
Advanced Tank Car Collaborative Research Program Executive Summary and Conclusions December 2016 

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TWP-4 - Sandwich Car Design 

The TWP-4 project (Sandwich Car Design) was identified as the best option for the advanced 

“car design platform” for the ATCCRP work. The sandwich car in this application was primarily 

considered to be a double tank or “tank-within-a-tank” concept here since the NGRTC program 

had found difficulties in getting improved puncture resistance in sandwich panels with crushable 

foam or engineered metal cores between the outer sandwich plates. For example, if the 

composite materials had been identified as providing enhanced puncture resistance, they could 

easily be incorporated in the outer tank structures of a sandwich design. 

A primary effort of the TWP-4 project was to evaluate the puncture performance of candidate 

tank car configurations in a suite of puncture analyses under various impact conditions 

(following the TWP-14 methodology). The designs featured baseline, retrofit, and sandwich 

tank design concepts for AA, EO, and Cl tank cars. Note that the effort was only to perform 

impact and puncture analyses on the tank systems and did not develop workable sandwich tank 

designs including inner tank supports, standoffs, bolsters and sills, or manway and top fittings. 

An example of the approach for side impacts on AA tank car designs are shown in Figure 6. 

Note that the puncture energies in this example are normalized by the functional fit to the 

baseline 112J340W tank analyses rather than to the individual 112J340W results for each impact 

scenario to reduce scatter. The 112J500I tank design (HM-246 interim specification car) has on 

average 90% greater puncture energy than the baseline 112J340W AA tank. Alternatively, the 

340 psi sandwich design with a 0.412-inch-thick TC128B jacket has similar puncture energy to 

the baseline 112J500I tank for square impactors. This is despite having approximately 6% less 

combined jacket thickness (1.03” compared to 1.10”). The sandwich 340 psi design shows 

increased puncture energy for large round impactors, and no improvement for the small round or 

the square impactors. 

A comparison of baseline and retrofit EO side impacts is shown in Figure 7. The baseline 

105J500I tank design (HM-246 interim specification car) has on average double the puncture 

energy of the baseline 105J300W EO tank. The baseline 105J500I and sandwich 300 psi designs 

have the same combined tank/jacket thickness (1.037”). Moving material from the tank to the 

jacket (baseline 105J500I to retrofit or sandwich 300 psi design) improved performance, 

especially for large impactors. The sandwich 300 psi design has on average 15% higher 

puncture energy than the 105J500I EO tank. 

A comparison of baseline, retrofit, and sandwich Cl tank side impacts is shown in Figure 8. The 

105J600I tank (HM-246 interim specification car) has on average 45% greater puncture energy 

than the baseline 105J500W Cl tank. The sandwich 300 psi design performed on average 10% 

better than the baseline 105J600I design. The greatest improvement is for small impactors. The 
Advanced Tank Car Collaborative Research Program Executive Summary and Conclusions December 2016 

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retrofit 500 psi design performed on average 5% better than the baseline 105J600I design. This 

is consistent with the approximately 5% greater total thickness (1.152” compared to 1.10”). 

Moving material from the tank to the jacket improved performance, but the benefit was not large. 

Figure 6. Relative side-impact puncture energies for AA tank designs 

Figure 7. Relative side-impact puncture energies for EO tank designs 
Advanced Tank Car Collaborative Research Program Executive Summary and Conclusions December 2016 

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Figure 8. Relative side impact puncture energies for Cl tank designs 

The primary conclusion of these comparisons of the various baseline, retrofit, and sandwich 

design concepts was that there were significant puncture improvements realized from the 

baseline legacy design to the improved HM-246 interim designs. These improvements were on 

average 90%, 100%, and 45% for the AA, EO, and Cl respectively. Comparison of the puncture 

performance of double tank sandwich concept to the HM-246 interim designs (using equivalent 

total thickness of the tank and jacket) resulted in much smaller incremental improvements than 

achieved by the interim specification cars over the baseline legacy tank designs. 

The one significant advantage of a double tank sandwich construction was that it could be more 

easily adapted to use the alternate candidate materials identified in TWP 10. A change in the 

steel for the commodity tank beyond the list of currently approved steels would require a 

significant effort to ensure reliability, durability, corrosion resistance, and safety at levels equal 

to or greater than existing steels. However, replacing the steel in the outer jacket would be much 

simpler under current approved design guidelines and could easily gain approval by the AAR 

Tank Car Committee. 

A secondary effort of the TWP-4 project was to evaluate the puncture performance of candidate 

sandwich tank car configurations using the steels identified under TWP-10 as having the highest 

puncture protection potential for the outer jacket material. The two materials evaluated are the 
Advanced Tank Car Collaborative Research Program Executive Summary and Conclusions December 2016 

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highest strength material that resulted in the largest tank puncture forces (HY-130) and the 

material with the highest puncture energy resistance (304L stainless steel). 

A comparison of sandwich AA tank side impacts with different jacket materials is shown in 

Figure 9. In this case, the puncture performance (energy) is normalized by the fit to the 

112J500I tank design (HM-246 interim specification car). The double tank 340 psi sandwich 

designs with either the TC128B or high strength steel (HY-130) jackets provide little benefit for 

this tank design. The 304L SS variation works well with on average approximately a 50% 

increase in puncture energy. Although there is improvement for all but the smallest (3-inch) 

impactor sizes, the greatest improvements are seen with large impactors. 

Figure 9. Relative side-impact puncture energies for AA jacket materials 

A comparison of sandwich EO tank side impacts with different jacket materials is shown in 

Figure 10 using the 105J500I design (HM-246 interim specification car) as the baseline to 

normalize the puncture energy. The jacket material was varied for the sandwich 300 psi EO tank. 

The standard sandwich design had a TC128B jacket. HY-130 and 304L stainless steel variations 

were tested. Both variations provide approximately 40-50% improvement in puncture energy for 

small impactors. However, the high strength HY-130 performance is not maintained for large 

impactors. The sandwich design with the 304L SS variation works well for all impactor sizes for 

the EO Sandwich tank. 
Advanced Tank Car Collaborative Research Program Executive Summary and Conclusions December 2016 

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Figure 10. Relative side-impact puncture energies for EO jacket materials 

Comparisons of sandwich Cl tank side impacts with different jacket materials are shown in 

Figure 11. In this case we are comparing double tank sandwich designs based on a 300 psi 

commodity tank (resulting in a thicker jacket) and the results are normalized to the 105J600I 

tank design (HM-246 interim specification car). The TC128B sandwich design provides on 

average approximately a 10% benefit with the largest benefit for small impactors. The HY-130 

and 304L stainless steel sandwich tank designs provide on average 40% and 80% improvements, 

respectively. (Note that these levels of improvement depend on idealized sandwich designs and 

puncture behavior that has not been validated against a full-scale impact test on these designs 

yet, and on failure models for these materials that were not characterized to the detailed level of 

other tank car materials, and therefore may not be reachable under real conditions.) The Cl tank 

results show similar performance trends to EO, where HY-130 strength improvement is greatest 

for small impactors and reduced for large impactors. 
Advanced Tank Car Collaborative Research Program Executive Summary and Conclusions December 2016 

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Figure 11. Relative side-impact puncture energies for Cl jacket materials 

TWP-22 - Development of Advanced Head Protection Concepts 

The TWP-22 project (Development of Advanced Head Protection Concepts) was initiated with a 

phase I effort to evaluate four double head protection concepts, as shown in Figure 13. The first 

two are for a double head system, with a large and small standoff distance between the heads. 

The third concept is a double thickness head. The fourth concept included an inverted internal 

head allowing a large standoff between the inner and outer heads. 

Puncture analyses were performed for these concepts with the baseline 6x6-inch square impactor 

in the baseline offset impact configuration. In all four cases the inner head was pressurized to 

100 psi. For comparison to a known baseline, it was assumed that each concept design is for a 

100-inch inside diameter tank intended for chlorine service. Each concept design was modeled 

to determine its ability to withstand puncture. 

The calculated force-deflection behaviors and calculated puncture energies for the offset impact 

with the 6-inch square impactor for the four systems are shown in Figure 12. The designs have 

significant variations in the peak puncture forces but all of the puncture energies were within 

approximately a 20 percent variation. For comparison, a pressurized 500 psi chlorine tank head 

with a flanged and dished 1⁄2-inch head shield was calculated in the NGRTC program to have a 

puncture force of 952,000 lbs and puncture energy of 1.1 million ft-lbs [1]. The concepts were 
Advanced Tank Car Collaborative Research Program Executive Summary and Conclusions December 2016 

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not found to provide significant benefits compared to more traditional head and head shield 

designs. 

Figure 12. Calculated force-deflection histories for the baseline head protection concepts. 

A secondary effort of the TWP-22 project was performed to investigate the effects of the tank 

constraint boundary conditions on the impact and puncture behavior. All of the head impact 

testing and the majority of the analyses in the NGRTC and ATCCRP efforts used a fully 

constrained tank head for the impact scenarios. The concern is that by not allowing the tank to 

move freely away from the impact, we may introduce a bias that benefits a particular type of 

design over another (e.g. a stiff design with a high puncture force vs. a compliant design with a 

lower puncture force. 

A secondary series of analyses were performed with the designs to evaluate the head impact 

performance on an unconstrained tank. The relaxed constraint had a large effect on the puncture 

energy as the impactor has to travel a larger distance to account for the motion of the tank. This 

impact energy is primarily converted to kinetic energy of the impacted tank. All of the head 

systems evaluated experienced between 92 and 100% increase in the puncture energy with the 

unconstrained impact scenario. However, the increases were approximately proportional and the 

relative ranking of the performance for the various systems was unchanged. As a result, the 

highly constrained impact scenario remains a valid approach for evaluating the performance of 

head protection designs. Note that a unconstrained side impact test configuration would also 

result in higher puncture energies. However, the relative increases in the side impact puncture 
Advanced Tank Car Collaborative Research Program Executive Summary and Conclusions December 2016 

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energies would be smaller since some movement of the tank center of gravity occurs as the tank 

is pushed against the wall (e.g. a partially constrained side impact configuration). 

 

 (a) Double Head – Large Standoff (b) Double Head – Small Standoff 

 (c) Double Thickness Head (d) Inverted Internal Head 

Figure 13. Models of the four baseline head protection concepts. 

 
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TWP-17 - Revising and Updating Conditional Probability of Release Estimates 

The TWP-17 project generated updated formulas for estimating FRA-reportable conditional 

probability of release (CPR) and quantity lost for each of the four car components (head, shell, 

top and bottom fittings), and for the whole car, for all “conventional” designs [14]. These 

formulas indicate which variables have a significant effect on each component CPR. 

The most recent previous report that provided CPR estimates had been RSI-AAR Safety Project 

report RA-05-02 [15]. The TWP-17 analyses updated that previous work, including all accident 

data from 1980-2011, and employed more robust approaches to the statistical analysis of the 

data. They also added several new variables not addressed in the previous RA-05-02 report 

including car features, train speed, derailment severity, etc. The ATCCRP-related objective of 

this effort was to support TWP-11 with the most powerful and up-to-date data available. 

“CPR” as defined in TWP-17 is the fraction of tank cars of a given description (i.e., the 

probability that one such tank car of that description) that will lose some quantity of lading from 

impact damage, given that they are derailed in an accident that requires a report from the railroad 

to the FRA. Damage and losses caused by exposure to heat are not part of the CPR calculation. 

TWP-17 produced CPR estimates for TIH cars as shown in Table 1. The table also compares the 

accident performance of interim specification cars to legacy cars that are used for the same 

commodity. 

 
Advanced Tank Car Collaborative Research Program Executive Summary and Conclusions December 2016 

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Table 1 

CPRs for Selected TIH Tank Cars 

Under Average Mainline Derailment Conditions* 

Chlorine 

Car Spec. Head 

Thickness 

(in.) 

Shell 

Thickness 

(in.) 

Jacket Head 

Shield

Shell 

Inside 

Diameter 

(in.) 

CPR Percent 

Improvement 

Over PreHM-246 

Baseline 

105A500W 0.812 0.775 Yes No 100.45 0.042 n/a 

105J600I 0.954 0.954 Yes Full 100.45 0.019 54.8 % 

Anhydrous Ammonia 

Car Spec. Head 

Thickness 

(in.) 

Shell 

Thickness 

(in.) 

Jacket Head 

Shield

Shell 

Inside 

Diameter 

(in.) 

CPR Percent 

Improvement 

Over PreHM-246 

Baseline 

112J340W 0.625 0.625 Yes Full 119 0.033 n/a 

112J500I 0.900 0.900 Yes Full 116.75 0.016 51.5 % 

Ethylene Oxide 

Car Spec. Head 

Thickness 

(in.) 

Shell 

Thickness 

(in.) 

Jacket Head 

Shield

Shell 

Inside 

Diameter 

(in.) 

CPR Percent 

Improvement 

Over PreHM-246 

Baseline 

105J300W 0.603 0.562 Yes Full 117.87 0.041 n/a 
Advanced Tank Car Collaborative Research Program Executive Summary and Conclusions December 2016 

22 

105J500I 0.900 0.900 Yes Full 116.75 0.016 61.0% 

* Train speed at time of derailment = 26 mph, 11 cars derailed, tank car is the 6th car derailed 

The car dimensions shown in Table 1 are meant to be illustrative. They are based on the most 

commonly built designs as of the publication of this report. 

TWP-11 - Relating Conditional Probability of Release to Modeling and Tests 

The TWP-11 project was needed to develop an analytical method to estimate CPR for tank cars 

or tank car design elements for which satisfactory empirical data on accident performance do not 

exist. It is necessary to bridge the gap between the statistical and the analytical/testing 

approaches in the NGTRC efforts and other ATCCRP projects in order to understand how new 

designs will perform in response to the distribution of forces tank cars experience in accidents 

and thus quantitatively estimate the effect on safety and risk. Quantitative improvements in tank 

puncture force/energy do not readily translate into estimates of improvements in risk via CPR 

estimates. Without this relationship, it is difficult to quantify the benefits of new designs. 

The TWP-11 project to date has been performed as a proof-of-concept Phase I effort. The 

approach was to perform a set of detailed derailment simulations for a range of derailment 

conditions and scenarios determined using a design of experiments approach. For the Phase I 

effort the scenarios were limited to a more specific set of derailments rather than trying to 

capture the entire range of possible events. These included derailments of trains within a defined 

range of speeds and train lengths on tangent track. The simulations determined the number and 

severity of impacts experienced by each tank car in all of the simulations. For any given 

distribution of impactor sizes, a corresponding number of tank punctures could also be obtained 

from the simulations. 

The calculated tank puncture probabilities in the derailment simulations were then compared to 

the expected probability each of the tanks would be punctured using the TWP-17 CPRs. 

Impactor size distributions were generated that minimize the differences between the simulated 

CPRs and TWP-17 CPRs. The results of the TWP-11 Phase I simulations resulted in a family of 

impactor size distributions that each provide equivalent correlations of the CPR. There is still 

significant work needed in an expanded Phase II effort to ensure that the simulations consider all 

the necessary parameters to be representative of the real world derailment environment. 
Advanced Tank Car Collaborative Research Program Executive Summary and Conclusions December 2016 

23 

1.3 Conclusions 

1.3.1 We have vastly improved our understanding of tank impact and puncture behaviors and 

developed a wealth of new experimental data and analytical results to support ongoing 

and future tank car safety efforts. 

The above summary provides a series of key findings and results from the ATCCRP and 

associated tank car safety research. The projects have created a large resource of new 

information that can be used to inform decision-making or rulemaking efforts. These 

include the relative performance of different tank designs for various commodities (Cl, 

AA, and EO). 

1.3.2 No new high technology design or material that produced significant new protection levels 

(e.g. composites, crushable foams, advanced engineered energy absorbing sandwich 

panels) has been identified. Traditional tank car designs with monolithic layers of good 

quality steel are relatively efficient structures for resisting the impact threats in the 

railroad safety environment. 

All of the work to date suggests that the standard tank and jacket construction (or double 

tank sandwich cars) is relatively efficient at resisting impacts and punctures and that 

advanced protection concepts (e.g. composites, crushable foams, and engineered metal 

sandwich panels) have not been found to produce increased protection levels. 

In an effort to improve on the interim specification car protection levels, various 

sandwich design concepts were also analyzed. Some improvements were possible with 

on average between 10%-20% increase in puncture energy in the double tank designs 

over the HM-246 interim specification tank designs. To achieve significant 

improvements over the interim specification cars required both the double tank sandwich 

car design and the use of exotic materials in the outer jacket such as 304L stainless steel 

or a 130 ksi high strength steel (HY130). For these designs, as much as an additional 

50% improvement over the HM-246 interim specification design was observed. 

However, it should be noted that these results were based on material models that were 

not characterized to the detailed level of other tank car materials and have not yet been 

proven in any full-scale impact testing. An improved characterization of 304L stainless 

steel is ongoing in the ATCCRP to partially address this shortcoming. 

1.3.3 The HM-246 interim specification cars provide a significant level of improvement over the 

legacy designs. The HM-246 interim specification car puncture energy improvements were 

on average 90%, 100%, and 45% for the anhydrous ammonia (AA), ethylene oxide (EO), 
Advanced Tank Car Collaborative Research Program Executive Summary and Conclusions December 2016 

24 

and chlorine (Cl) cars respectively. Empirically-derived probabilities of lading release for 

interim specification cars were 51% to 61% lower than those of legacy cars. 

Another finding is that the HM-246 interim specification cars provide a significant 

advancement in puncture protection over the legacy designs. The HM-246 interim 

specification car puncture energy improvements were on average 90%, 100%, and 45% 

for the AA, EO, and Cl respectively. Empirically-derived CPR estimates support this 

finding: CPRs for interim specification cars were 51% to 61% lower than those of legacy 

cars. In addition, retrofit designs where the legacy design tank was retrofit with a 

correspondingly thicker jacket to achieve an equivalent combined thickness of tank and 

jacket as the HM-246 interim specification car achieved comparable puncture protection 

levels. 

1.3.4 The only option identified for possible improvements in puncture protection over the HM246 interim specification car designs are potential optimized sandwich designs, requiring 

alternative steels in the jacket (outer tank) for enhanced puncture protection. This 

conclusion is based on puncture analyses performed for various tank design 

configurations. Functional tank car designs for these sandwich cars were not developed 

in the research and the protection levels have not been proven by testing. 

References 

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Technical Report, Prepared for the Next Generation Railroad Tank Car (NGRTC) Project, 

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Enhancing Puncture Resistance in Railroad Tank Cars Carrying Hazardous Materials: Phase 

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