U.S. Department of 

Transportation

Federal Railroad 

Administration

Prototype Design of a Collision Protection 

System for Cab Car Engineers

Office of Research 

and Development

Washington, DC 20590

DOT/FRA/ORD-13/15 Final Report

March 2013
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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE

March 2013

3. REPORT TYPE AND DATES COVERED

Final Report April 2012

4. TITLE AND SUBTITLE

Prototype Design of a Collision Protection System for Cab Car Engineers

5. FUNDING NUMBERS

RR28A2/HL022

6. AUTHOR(S)

Anand Prabhakaran, Som P. Singh, and Anand R. Vithani

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

Sharma &Associates, Inc.

100 W. Plainfield Road

Countryside, IL 60525

8. PERFORMING ORGANIZATION

REPORT NUMBER

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

U.S. Department of Transportation 

Federal Railroad Administration

Office of Railroad Policy and Development

Office of Research and Development

Washington, DC 20590

10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

DOT/FRA/ORD-13/15

11. SUPPLEMENTARY NOTES

U.S. Department of Transportation

Research and Innovative Technology Administration

John A. Volpe National Transportation Systems Center

55 Broadway

Cambridge, MA 02142-1093

12a. DISTRIBUTION/AVAILABILITY STATEMENT

This document is available to the public through the FRA Web site at http://www.fra.dot.gov.

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

The objective of this project was to develop and analyze a passive system to protect a cab car engineer from secondary impact 

injuries that might be experienced due to impact with the cab console. The primary requirement for the system was the ability to 

compartmentalize and limit the injury indices for a 95th percentile Anthropomorphic Test Device (ATD). A baseline cab console 

was modified with an airbag and a crushable knee bolster to meet this objective. A computer model of an ATD impacting the cab 

console was validated using results from component-level tests. The modeling results indicate that the engineer protection system 

is capable of meeting the performance requirements. Subsequent work is planned to build and test the proposed system.

14. SUBJECT TERMS

Crashworthiness, cab console, secondary impact protection, airbags, energy absorption, 

crushable knee bolster, quasi-static testing, crash energy management, injury indices, finite 

element analysis

15. NUMBER OF PAGES

114

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NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. 239-18

298-102
ii

METRIC/ENGLISH CONVERSION FACTORS

ENGLISH TO METRIC METRIC TO ENGLISH

LENGTH (APPROXIMATE) LENGTH (APPROXIMATE)

1 inch (in) = 2.5 centimeters (cm) 1 millimeter (mm) = 0.04 inch (in)

1 foot (ft) = 30 centimeters (cm) 1 centimeter (cm) = 0.4 inch (in)

1 yard (yd) = 0.9 meter (m) 1 meter (m) = 3.3 feet (ft)

1 mile (mi) = 1.6 kilometers (km) 1 meter (m) = 1.1 yards (yd)

1 kilometer (km) = 0.6 mile (mi)

AREA (APPROXIMATE) AREA (APPROXIMATE)

1 square inch (sq in, in2) = 6.5 square centimeters (cm2) 1 square centimeter (cm2) = 0.16 square inch (sq in, in2)

1 square foot (sq ft, ft2) = 0.09 square meter (m2) 1 square meter (m2) = 1.2 square yards (sq yd, yd2)

1 square yard (sq yd, yd2) = 0.8 square meter (m2) 1 square kilometer (km2) = 0.4 square mile (sq mi, mi2)

1 square mile (sq mi, mi2) = 2.6 square kilometers (km2) 10,000 square meters (m2) = 1 hectare (ha) = 2.5 acres

1 acre = 0.4 hectare (he) = 4,000 square meters (m2)

MASS - WEIGHT (APPROXIMATE) MASS - WEIGHT (APPROXIMATE)

1 ounce (oz) = 28 grams (gm) 1 gram (gm) = 0.036 ounce (oz)

1 pound (lb) = 0.45 kilogram (kg) 1 kilogram (kg) = 2.2 pounds (lb)

1 short ton = 2,000 pounds 

(lb)

= 0.9 tonne (t) 1 tonne (t) =

=

1,000 kilograms (kg)

1.1 short tons

VOLUME (APPROXIMATE) VOLUME (APPROXIMATE)

1 teaspoon (tsp) = 5 milliliters (ml) 1 milliliter (ml) = 0.03 fluid ounce (fl oz)

1 tablespoon (tbsp) = 15 milliliters (ml) 1 liter (l) = 2.1 pints (pt)

1 fluid ounce (fl oz) = 30 milliliters (ml) 1 liter (l) = 1.06 quarts (qt)

1 cup (c) = 0.24 liter (l) 1 liter (l) = 0.26 gallon (gal)

1 pint (pt) = 0.47 liter (l)

1 quart (qt) = 0.96 liter (l)

1 gallon (gal) = 3.8 liters (l)

1 cubic foot (cu ft, ft3) = 0.03 cubic meter (m3) 1 cubic meter (m3) = 36 cubic feet (cu ft, ft3)

1 cubic yard (cu yd, yd3) = 0.76 cubic meter (m3) 1 cubic meter (m3) = 1.3 cubic yards (cu yd, yd3)

TEMPERATURE (EXACT) TEMPERATURE (EXACT)

[(x-32)(5/9)] °F = y °C [(9/5) y + 32] °C = x °F

QUICK INCH - CENTIMETER LENGTH CONVERSION

0 1 2 3 4 5

Inches

Centimeters 0 1 2 3 4 5 6 7 8 9 10 11 12 13

QUICK FAHRENHEIT - CELSIUS TEMPERATURE CONVERSIO

 -40° -22° -4° 14° 32° 50° 68° 86° 104° 122° 140° 158° 176° 194° 212°

 

°F

 °C -40° -30° -20° -10° 0° 10° 20° 30° 40° 50° 60° 70° 80° 90° 100°

For more exact and or other conversion factors, see NIST Miscellaneous Publication 286, Units of Weights and 

Measures. Price $2.50 SD Catalog No. C13 10286 Updated 6/17/98
iii

Contents

Executive Summary...........................................................................................1

1. Background.................................................................................................................. 5

2. Objectives and Scope .................................................................................................. 6

2.1 Scope ........................................................................................................................... 6

2.2 Performance Requirements ......................................................................................... 6

2.2.1 Cab Performance ......................................................................................................... 7

2.2.2 Occupant Response ..................................................................................................... 7

2.2.3 Compartmentalization ................................................................................................. 8

3. Development of a Baseline Cab Layout...................................................................... 9

3.1 Cab Studies and Measurements................................................................................... 9

3.2 Key Measurements.................................................................................................... 11

3.3 Baseline Composite Cab Layout ............................................................................... 15

3.4 Summary ................................................................................................................... 17

4. Review of Protection Strategies and Standards......................................................... 18

5. Concept Development ............................................................................................... 21

5.1 Development of Concepts......................................................................................... 21

5.2 Preliminary Evaluation of Concept Viability............................................................ 24

5.2.1 Key Results................................................................................................................ 24

5.3 Summary ................................................................................................................... 25

6. Detailed Design ......................................................................................................... 27

6.1 Airbag System Design............................................................................................... 27

6.2 Knee Bolster Design.................................................................................................. 31

6.3 Design Evaluation ..................................................................................................... 35

6.3.1 Simulation Results..................................................................................................... 37

6.4 Weight and Cost ........................................................................................................ 40

6.5 Summary ................................................................................................................... 40

7. Component Characterization..................................................................................... 41

7.1 Airbag Characterization ............................................................................................ 41

7.1.1 Airbag Static Deployment Tests................................................................................ 41

7.1.2 Airbag Drop Tower Tests.......................................................................................... 43

7.1.3 Airbag Model Characterization................................................................................. 50

7.2 Knee Bolster Testing................................................................................................. 54

7.2.1 Honeycomb Crush Tests ........................................................................................... 54

Knee Bolster Bracket Tests................................................................................................... 59

7.3 Summary ................................................................................................................... 62

8. Post-Characterization System Performance .............................................................. 64
iv

8.1 Results....................................................................................................................... 66

9. Conclusions and Recommendations.......................................................................... 69

10. References ................................................................................................................. 70

A.1 AUTOMOTIVE OCCUPANT PROTECTION STRATEGIES................................. 1

APPENDIX B. BRAINSTORM SESSION TO GENERATE CONCEPTS FOR THE 

PROTECTION SYSTEM............................................................................................................. 14

APPENDIX C. EVALUATION OF POTENTIAL CONCEPTS FOR THE PROTECTION 

SYSTEM 18

APPENDIX D. PRELIMINARY EVALUATION OF CONCEPT VIABILITY....................... 20

SUMMARY.......................................................................................................................... 29

APPENDIX A. Strategy and Standards Review...................................................... A1

APPENDIX B. Brainstorm Session to Generate Concepts for the Protection System......... A14

APPENDIX C. Evaluation of Potential Concepts for the Protection System.....................A18

APPENDIX D. Preliminary Evaluation of Concept Viability.................................... A20

APPENDIX E. Injury Index Plots – Final Run........................................................A30
v

Illustrations

Figure 1. Crash Acceleration Pulse and Secondary Impact Velocity for EPS Test Requirements 7

Figure 2. Engineer Chair, Console, and Control Panel Layout for the LIRR Cab Car................ 10

Figure 3. Metra Car Cab Console Views – Top of and Underneath the Engineer Desk ............. 10

Figure 4. Metrolink Car Cab Console Views............................................................................... 11

Figure 5. CAD Representations of Measured Cab Consoles....................................................... 14

Figure 6. Summary of the Reviewed Cab Geometric Dimensions and the Proposed Cab 

Parameters............................................................................................................................. 16

Figure 7. Composite Cab Layout................................................................................................. 17

Figure 8. Occupant Protection System - Concept 1 – Airbag + Knee Bolster............................. 23

Figure 9. Occupant Protection System - Concept 2 – ITS + Knee Airbag .................................. 23

Figure 10. Airbag Shape .............................................................................................................. 27

Figure 11. Airbag Module Details............................................................................................... 28

Figure 12. Airbag Assembly Components................................................................................... 29

Figure 13. Airbag Housing Dimensions ...................................................................................... 30

Figure 14. PH-5 Inflator............................................................................................................... 30

Figure 15. Output from a 60 Liter Inflation Test – PH5 Inflator................................................. 31

Figure 16. Baseline Cab Structure Finite Element Model ........................................................... 32

Figure 17. Force versus Deflection – Preliminary Knee Bolster Design..................................... 33

Figure 18. Knee Bolster System Assembly (Left)....................................................................... 34

Figure 19. Dimensions of Knee Bolster Bracket ......................................................................... 35

Figure 20. Baseline Sled Test Finite Element Model .................................................................. 36

Figure 21. Designed System (Pre-Characterization) – Simulation Screen Shots........................ 38

Figure 22. Simulation Results – Designed System (Pre-Characterization)................................. 39

Figure 23. Drop Tower Test Setup .............................................................................................. 42

Figure 24. Sequence of Airbag Inflation for Static Deployment Test ......................................... 43

Figure 25. Airbag Drop Tower Test Frame ................................................................................. 45

Figure 26. Airbag Drop Tower Test Frame ................................................................................. 45

Figure 27. Measured and Computed Data – Drop Tower Test #1............................................... 47

Figure 28. Measured and Computed Data – Drop Tower Test #2............................................... 48

Figure 29. Cushion Kinematics – Drop Tower Test Series #2 .................................................... 49

Figure 30. MADYMO Drop Tower Test Model ......................................................................... 51

Figure 31. MADYMO Characterized Data – Unvented Airbag.................................................. 52
vi

Figure 32. Characterization Data – RADIOSS Drop Test Model ............................................... 53

Figure 33. Schematic of the Honeycomb Sample Test Fixture ................................................... 55

Figure 34. Honeycomb Sample in the Test Frame ...................................................................... 56

Figure 35. Crush Honeycomb Sample (Left) and Individual Layers in Crushed State (Right)... 56

Figure 36. Crush Force versus Displacement Characteristics for the Honeycomb Sample ........ 57

Figure 37. Model and Characterization of Honeycomb Block .................................................... 58

Figure 38. Schematic of the Knee Bracket Test Fixture.............................................................. 60

Figure 39. Knee Bracket Sample in the Load Test Frame........................................................... 60

Figure 40. Knee Bolster Bracket Specimen – Permanently Deformed Under Load ................... 61

Figure 41. Knee Bolster Bracket Specimen – Pre- and Post-Test Traces.................................... 61

Figure 42. Knee Bolster Bracket Force Deflection Characteristics for the Two Specimens....... 62

Figure 43. RADIOSS Model of Knee Bracket Test Setup .......................................................... 63

Figure 44. Test and RADIOSS Model Force-Deflection Results for the Knee Brackets............ 63

Figure 45. RADIOSS Model of Engineer Protection System Inclusive of Airbag and Knee 

Bolster Assembly-3-D View and a Sectional Side View...................................................... 65

Figure 46. ATD Kinematics for the Proposed Design................................................................. 67

Figure 47. Predicted Normalized Injury Indices for Final Design of Engineer Protection System

............................................................................................................................................... 68
vii

Tables

Table 1. Performance of the Engineer Protection System (EPS)................................................... 3

Table 2. Test Crash Pulse............................................................................................................... 7

Table 3. Limiting Injury Indices.................................................................................................... 8

Table 4. Summary – Control Desk Architecture of the Surveyed Cabs...................................... 11

Table 5. Spatial Layout Summary of the Surveyed Cabs............................................................ 12

Table 6. Summary – Cab Construction Materials........................................................................ 13

Table 7. Proposed Cab Geometry Dimensions............................................................................ 15

Table 8. Cab Equipment .............................................................................................................. 16

Table 9. Summary of the Railway Vehicle Interior Design and Occupant Protection 

Recommended Practices and Standards................................................................................ 19

Table 10. Summary of Automotive Crashworthiness Standards................................................. 20

Table 11. Evaluation Criteria and Weights for Cab Occupant Protection System Concepts...... 22

Table 12. Selected Concept Elements for Head, Torso, and Femur Protection........................... 22

Table 13. MADYMOTM Simulation Results for the Two Concepts and the Baseline ................ 25

Table 14. Injury Indices – Design System (Pre-Characterization) Sled Test Model................... 37

Table 15. Component Weights .................................................................................................... 40

Table 16. System Material Costs................................................................................................. 40

Table 17. Drop Tower Test Parameters....................................................................................... 44

Table 18. Final Model Parameters............................................................................................... 64

Table 19. Performance of the EPS............................................................................................... 66
1

Executive Summary

Passenger trains are an extremely safe mode of travel in the United States. However, several 

train accidents over the last few years, coupled with the availability of newer technologies that 

could lead to safer rail travel, have prompted significant research into the science of train 

crashworthiness. The Federal Railroad Administration (FRA) has been funding crashworthiness 

research, and the John A. Volpe National Transportation Systems Center (Volpe) has been 

conducting pioneering research work in support of FRA. The research approach has been to 

propose strategies for improved crashworthiness and to apply analytical tools and testing 

techniques for evaluating the effectiveness of those strategies.

In a rail vehicle collision, the cab or locomotive engineer is in a vulnerable position at the 

leading end of the vehicle. In commuter train accidents with a conventional cab car leading, the 

control cab often suffers the most damage because there is little energy-absorbing structure 

between the occupied control cab and the front of the car. As cars with increased 

crashworthiness are introduced to the market, there is the potential to preserve survival space for 

the engineer. When sufficient survival space is preserved, the next objective is to protect the 

engineer from the injurious and potentially fatal forces and accelerations associated with 

secondary impact. 

The objective of this project was to develop, analyze, fabricate, test, and validate a passive 

system to protect a cab car engineer from secondary impact injuries that might be experienced in 

moderate collision conditions. For this effort, the collision condition has been defined as a 

trapezoidal deceleration pulse with a peak of 23g and duration of 130 milliseconds (the 

‘Engineer Protection System (EPS) Test Pulse’). Below are the key functional requirements for 

the system:

• Compartmentalize and limit the injury indices for a 95th percentile Anthropomorphic Test 

Device (ATD) to values that are below those currently specified in Federal Motor 

Vehicle Safety Standards (FMVSS) 208

• Require no input or action by the engineer

• Allow for unencumbered exit of the engineer (current regulations, operating procedures, 

crew preferences, etc. do not allow the use of any seatbelt or like restraints)

• Be capable of being adapted or modified for existing cab cars and locomotives

To better understand the layout in cab cars and to avoid developing concepts and strategies that 

were too specific to any particular cab design, cab layouts from four agencies were studied: 

Metrolink in Los Angeles, CA; Metra in Chicago, IL; Long Island Railroad (LIRR) in New 

York; and Northern Indiana Commuter Transportation District (NICTD) in Chesterton, IN. The 

effort focused on identifying critical functional, operational, and ergonomic parameters such as 

space availability, locations of throttle and braking controls, instruments, seat position, etc., with 

a special emphasis on the location, size, and shape of exposed control levers (i.e. surfaces likely 

to pose an injury threat during a crash). The cab review also made it clear that the operator cab is 

a highly confined space with densely positioned equipment, which makes it hard to find room for 

new safety items or devices.

Based on the cab review, a composite cab layout was developed that was:

• Reasonably representative of existing cabs
2

• Consistent with cab occupant protection strategies, and 

• Capable of meeting functional, safety, and ergonomic requirements.

As part of the preliminary research effort, the current standards, injury criteria, state-of-the-art 

technologies, and strategies of the automotive, heavy vehicle, and railway industry were 

reviewed. This effort provided critical insight into the applicability, strengths, and weaknesses 

of potential strategies and technology solutions. The protection strategies used in the automotive 

industry offered elements that could be adapted for railroad application. For example, while 

most current automotive strategies focus on protecting a belted occupant, the automotive 

industry has a long history of providing a nominal level of protection to unbelted occupants. 

Several concepts that provide protection to the head, chest, torso, and femur areas were 

generated through a brainstorming process. Those concepts were evaluated with the following 

criteria in mind: 

o Feasibility and acceptability

o Development timeframe

o Likelihood of success 

o Contribution to overall success of strategy

o Injury index reduction

o Compartmentalization

o Egress

o Design simplicity

o Maintenance

o Comfort and ergonomics

o Weight increase

o Material and manufacturing costs

Generated concepts were ranked by a panel according to the above characteristics (weighted 

appropriately), and the following two were selected for further evaluation:

• Automotive passenger-style airbag with a crushable knee bolster

• Inflated Tubular Structures (ITS) with a knee airbag or crushable knee bolster

The potential effectiveness of each concept was evaluated using preliminary MADYMOTM sled 

test simulations with the specified EPS test pulse and a 95th percentile ATD in the seat. A 

baseline case with no passive occupant protection features was also evaluated for benchmarking 

purposes.

For the baseline case, the simulations predicted injury indices well in excess of the prescribed 

limits. As expected, both concepts showed significant improvements in injury indices compared 

to the baseline case. Concept 1 (passenger-style airbag with knee bolster) showed better injury 

prevention or mitigation performance compared with Concept 2 (ITS with knee airbag/knee 

bolster), including the potential for injury indices to be within 80 percent of the limits and 

improved ATD kinematics. Therefore, for this project, Concept 1 was selected for further design 

and development efforts.
3

Concept 1 was then developed into a detailed design and subsequently integrated into the 

composite cab layout. After several design iterations, a promising arrangement for the knee 

bolster was determined to be a combination of a honeycomb structure and a pair of deformable 

brackets. The airbag was a custom design similar to those typically used in the passenger side of 

an automobile. It was placed with the inflator and airbag housing in the operator’s desk, which 

allowed for optimum protection for a range of occupant positions. 

This design was then modeled in detail using RADIOSS, an explicit solver, and evaluated under 

the prescribed 23g pulse. These detailed simulations showed that the design would meet the 

safety performance goals with a comfortable margin. Various properties of the airbag and knee 

bolster system had been defined using theoretical design values. In order to gain confidence in 

the simulation results, the airbag, honeycomb, and deformable brackets were tested individually 

and compared with individual FE simulations that replicated the corresponding tests. This 

provided a set of verified properties for individual elements of the protection system.

The final design of the EPS, which incorporated the airbag and knee bolster data from the 

characterization tests, was evaluated with a 95th percentile ATD under the specified 23g crash 

pulse using an updated RADIOSS model. The simulation results (presented in the table below)

show that the proposed cab EPS is expected to meet the targeted safety performance with 

comfortable margins.

Table 1. Performance of the Engineer Protection System (EPS)

Injury Parameter Index 

Limit

Calculated Injury Indices (RADIOSS Model)

Base 

Case

Pre-Component 

Characterization Test

Post-Component 

Characterization Test

HIC_15 700 9,661 104 87

Chest 3ms (g) 60 38 38 35

Femur Left (N) 10,000 20,307 7,611 7,318

Femur Right (N) 10,000 20,236 7,743 6,924

Neck Tension (N) 4,170 5,089 2,177 2,504

Neck Compression (N) 4,000 2,525 934 543

Neck Injury Criterion

(Tension-Extension), Nte

1.0 1.39 0.60 0.77

Neck Injury Criterion 

(Tension-Flexion), Ntf

1.0 1.07 0.25 0.29

Neck Injury Criterion 

(Compression-Extension), Nce

1.0 0.28 0.26 0.18

Neck Injury Criterion 

(Compression-Flexion), Ncf

1.0 0.82 0.26 0.25

The system is expected to add approximately 30 pounds (lb) to the car weight, which is minimal 

considering the safety benefits offered. The cost of these systems is likely to vary significantly 

depending on volume. For small volumes (100 or fewer units per year), initial estimates of 

material cost indicate that the system is likely to add about $3,000 per equipped cab.
4

The results, and the rigorous process followed to arrive at this concept, provide reasonable 

confidence in the value of proceeding to the next phase of the protection system development. 

Also, simulation results from various intermediate configurations indicate that the resulting 

injury indices are not overly sensitive to minor variations in properties of design elements. In 

other words, reasonable design flexibility is available to achieve the specified injury protection 

criteria. Therefore, the protection system can be adjusted to accommodate other considerations, 

such as ATD categories, car designs, etc.

We recommend that the performance of the proposed system be verified through a full-scale sled 

test and subsequent model validation in the next phase of the effort. 
5

1. Background

Although passenger trains are an extremely safe mode of travel in the United States, several train 

accidents over the last few years, as well as the availability of newer technologies that could lead 

to safer rail travel, have prompted significant research and development into train 

crashworthiness. This research program was sponsored by FRA’s Office of Research and 

Development in support of improved safety standards for passenger rail vehicles.

In a rail vehicle collision (i.e., a passenger train accident), the cab or locomotive engineer is in a 

vulnerable position at the leading end of the vehicle. In accidents with a conventional cab car 

leading, the control cab often suffers the most damage given that there is little energy-absorbing 

structure between the occupied control cab and the front of the car. As cars with increased 

crashworthiness are introduced to the market, there is potential for preserving occupant space for 

the engineer. In particular, full-scale impact tests have demonstrated that the engineer’s space 

can be preserved at closing speeds up to 30 mph.

When sufficient survival space is preserved, the next imperative is to protect the engineer from 

the forces and accelerations associated with secondary impact. Secondary impact occurs when 

the rail vehicle decelerates or accelerates suddenly due to collision forces and the occupants of 

the rail vehicle strike some part of the interior. Given the hard surfaces and protruding knobs 

and controls in an operator cab, even a low speed collision can result in large, concentrated 

forces acting upon the engineer. 

Hence, there is a significant need to develop ‘Engineer Protection Systems’ that can protect cab 

car engineers in frontal collisions (a common mode of train collision) from secondary impact 

injuries. Given the particular vulnerability of cab cars under these collision conditions, the initial 

focus is on cab cars. However, the concepts developed through this effort and the process 

followed could be extended in the future to freight and passenger locomotives.

The intent of this effort has been to develop a passive (i.e. without active input from the 

engineer) interior protection strategy for cab car and locomotive engineers, assuming that the rail 

car structure can preserve adequate survival space for the engineer. The occupant protection 

strategy should protect engineers from the secondary impact that occurs when the engineer 

strikes the control console.
6

2. Objectives and Scope

The objective of this project was to develop, analyze, fabricate, test, and validate injury 

prevention and mitigation strategies to protect a cab car engineer under collision conditions 

similar to those of the full-scale multilevel car test. The selected strategy and corresponding 

design will have the following key characteristics:

• Protect engineers from the secondary impact that occurs following a frontal train collision 

when the engineer strikes the control console.

• Require no action from the operator to trigger the system. 

• Allow for unencumbered exit of the engineer. Seatbelts or other systems that must be 

disengaged before the operator can flee the cab will not be incorporated into the design. 

A successful protection strategy must not inhibit the engineer from emergency egress.

• Provide compartmentalization of a 95th percentile anthropomorphic test device (ATD) 

and measured injury criteria for the ATD’s head, chest, neck, and femur that are below 

the limits currently specified in the Federal Motor Vehicle Safety Standards (FMVSS) 

208 [1], when tested under the EPS Test Pulse (see figure 1).

2.1 Scope

The scope of this project is to develop a passive (i.e. not requiring operator input) safety system 

for a train engineer in a cab car, and includes the following objectives:

• Develop a representative and generic control stand geometry, applicable to cab cars, with 

the appropriate material and space representations.

• Develop design concepts to protect the engineer from secondary impacts, following the 

key criteria outlined above.

• Identify the most promising design concept in consultation with Volpe and develop the 

concept into a design suitable for evaluation.

• Evaluate the performance of the selected concept for compliance with FMVSS criteria, 

using the appropriate analytical techniques, and refine the design as needed to meet those 

requirements.

• Develop, build, and characterize by test, the individual components that make up the 

system, and update the analytical models based on the test results. 

• Re-evaluate system performance using the revised component models, and update the 

design, if needed, to meet FMVSS performance requirements.

2.2 Performance Requirements

The occupant protection system shall be designed to limit human injury to a 95th percentile, 

Hybrid III, male ATD, to the injury criteria values outlined in section 2.2.2, when subjected to 

the EPS test pulse defined in section 2.2.1. The system shall also effectively compartmentalize 

the occupant as outlined in 2.2.3. System performance shall be demonstrated under dynamic 

sled test conditions performed in accordance with 49 CFR Part 572, Subparts B and E, with the
7

ATD positioned in accordance with SAE AS8049. An analytical demonstration is intended 

under this (currently reported) phase of the effort, and a physical demonstration is planned under 

the next phase.

2.2.1 Cab Performance

The occupant protection system should be designed to be effective when subjected to the 

acceleration pulse and the corresponding secondary impact velocity (SIV) profile shown in

Figure 1. This test pulse has an SIV similar to the SIV from the multilevel single car test [2].

The crash pulse is hereinafter referred to as the ‘EPS Test Pulse’ and is outlined in Table 2.

Table 2. Test Crash Pulse

Time (s) Acc. (g)

0.00 0.0

0.01 23.0

0.03 23.0

0.13 0.0

2.2.2 Occupant Response

The injury measurements taken by the ATD must meet the following criteria, which are derived 

from CFR 49 Part 571, Standard No. 208; Occupant crash protection.

0

5

10

15

20

25

30

35

40

45

0 0.5 1 1.5 2 2.5 3

Distance (ft)

Velocity (mph)

Multi-level Test

Trapezoid Pulse

Trapezoidal Pulse

0

5

10

15

20

25

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

Time (s)

Acceleration (g)

Figure 1. Crash Acceleration Pulse and Secondary Impact Velocity for EPS Test 

Requirements
8

Table 3. Limiting Injury Indices

Injury Criterion Limiting Value

HIC15 <700

Nij <1.0

Neck Tension <937 lbf (4,170 N)

Neck Compression <899 lbf (4,000 N)

Chest Deceleration <60g over a 3ms clip

Axial Femur Loads <2,250 lbf (10,000 N)

2.2.3 Compartmentalization

Occupant kinematics should demonstrate that the occupant is effectively compartmentalized 

within the cab area by the occupant protection system. For this effort, compartmentalization is a 

design strategy that aims to contain the engineer between his or her seat and the console during a 

collision, preventing the engineer from traveling over consoles and impacting other hostile 

objects. During sled testing, ATD compartmentalization is evaluated up until the point of 

maximum forward progress of the ATD. The ATD must be confined between the console 

(potentially deformed) and the seat until the ATD begins to rebound and move away from the 

impacted console.

The following sections address and describe these tasks along with the underlying approach used

to achieve the associated objective(s) and the results accomplished. 
9

3. Development of a Baseline Cab Layout

As noted, the focus of this study is on developing concepts to improve the survivability of 

engineers in cab cars under a frontal collision scenario. Traditionally, cab cars have a relatively 

cramped operator layout with a high probability for impact with hostile surfaces during an 

accident. While most cab car configurations use a desk style control stand, there are significant 

variations in layout. To avoid developing a concept too specific to one design or layout, we

conducted a comprehensive review of several existing cab car configurations used in commuter 

train operations. The goal of these reviews was to gather information and data on cab layout and 

cab designs that are currently in use, with respect to engineer seating, control layout, spatial 

considerations, etc. These data describe the overall cab layout, including geometry, protrusions, 

materials, seat layout, measurements, and photographs. Subsequently, key and common 

elements of the design were extracted to develop a ‘baseline’ cab, on which subsequent work 

was based.

3.1 Cab Studies and Measurements

Cab information was gathered from four large commuter rail operators:

1. Metrolink in Los Angeles, California

2. Metra in Chicago, Illinois

3. Long Island Railroad (LIRR) in New York

4. Northern Indiana Commuter Transportation District (NICTD) in Chesterton, Indiana 

The Metra cab car and the NICTD EMU car were manufactured by Nippon Sharyo. LIRR cab 

cars were built by Kawasaki Heavy Industries, Ltd. Metrolink cab cars were built by 

Bombardier, Inc. Photographs of the cabs for the LIRR, Metrolink, and Metra cabs are shown in 

Figure 2, Figure 3, and Figure 4, respectively.
10

Figure 2. Engineer Chair, Console, and Control Panel Layout for the LIRR Cab 

Car

Figure 3. Metra Car Cab Console Views – Top of and Underneath the Engineer Desk
11

3.2 Key Measurements

To facilitate a comparative evaluation of the cab from architectural, spatial, and construction 

perspectives, measurements of cab dimensions, location of throttle and brake controls, engineer 

seat height and location relative to the console and cab walls were made. Information was 

collected on the materials used for various cab elements. The architectural, geometry, and 

material data are shown in the following tables.

Table 4. Summary – Control Desk Architecture of the Surveyed Cabs

LIRR Metra Metrolink NICTD

Has overhead 

console?

No Yes Yes Yes

Has left control 

panel?

Yes Just an LCD 

screen

Yes Yes

Has right control 

panel?

Yes No No No

Has footrest? Yes No Yes No

Exposed 

equipment under 

desk?

Sparsely 

populated

Densely 

populated

Sparsely 

populated

Sparsely 

populated

Throttle controller 

location

Control desk –

center

Control desk –

center

Control desk –

right

Control desk –

center right

Brake controller 

location

Control desk –

center

Control desk –

right

Control desk –

left

Control desk –

center right

Has foot operated 

switches?

Yes, both feet Yes, left foot Yes, left foot Yes, left foot

Has armrests on 

seats?

No Yes No Yes

Figure 4. Metrolink Car Cab Console Views
12

It may be noticed from Table 4 that, generally, cabs have extensive equipment under the desk 

protruding into the engineer’s knee area. The throttle controller is generally either in the center 

or right of the engineer’s seat. In some cases, the brake controller is located with the throttle 

controller in the center. The armrest and footrest are not standard features.

The geometric dimensions of the four cabs are shown in Table 5. The most important 

dimensions in the table in terms of injury potential from secondary collision are seat base to desk 

edge clearance, height of desk edge from cab floor, and the clearance from the engineer’s torso 

position to the desk edge. These parameters range from 13.5 to 18.5 inches (in), 26.5 to 30.63 in,

and 5 to 14.7 in, respectively. The wide range of the torso to desk edge clearance is due to the 6

in longitudinal adjustment to the engineer’s seat to accommodate a range of femur lengths.

Table 5. Spatial Layout Summary of the Surveyed Cabs

LIRR Metra Metrolink NICTD

Chair base column to edge of control 

desk 18.5 in 13.5 in 14 in 13.5 in

Longitudinal seat adjustment range 6 in 6 in No Data 6 in

Chair base column to right wall 15.25 in 15.5 in 14 in 15.5 in

Height of desk leading edge from floor 29.5 in 30 in 26.5 and 

30.63 in 30 in

Height of desk edge on the far side 36.5 in 35.5 in 38 in 36 in

Torso – desk longitudinal clearance** 12.5– 18.5 in 5– 11 in 8.7– 14.7 in 5– 11 in

Torso – controller longitudinal 

clearance** 13– 19 in 7.5– 13.5 in 7– 13 in 12– 18 in

Knee – desk longitudinal clearance* -1– 5 in -2– 4 in -2– 4 in -3– 3 in

Chair base column to edge of control 

desk 18.5 in 13.5 in 14 in 13.5 in

* Seat adjustment range assumed to be 6 in

** Clearances are approximate and based on a sitting position with feet on the floor and thighs parallel to the floor.

The materials used in the cabs for the control desk, left and right control panel, seat and footrest 

are listed in Table 6. In all cases, the control desk and engineer seat base are constructed of steel. 

The seat bottom and back are made of foam and the control panels are made of plastic with 

housing constructed of steel.
13

Table 6. Summary – Cab Construction Materials

LIRR Metra Metrolink NICTD

Left control 

panel

Mainly steel, bank of 

plastic coated 

switches

LCD screen in 

steel housing

Mainly steel, bank of 

plastic coated 

switches

LCD screen in 

steel housing, steel 

panel

Right control 

panel

Mainly steel, bank of 

plastic coated 

switches

N/A N/A N/A

Control desk Steel Steel Steel Steel

Footrest Steel N/A Steel NA

Seat Steel base and 

column, foam seat

Steel base and 

column, foam 

seat

Steel base and 

column, foam seat

Steel base and 

column, foam seat

To help develop an overall perspective for these cab layouts, Computer Aided Design (CAD) 

models were developed using the geometric measurements listed in Table 5. The CAD models 

permitted the team to study the layouts from various views—plan, end, side, and cross 

sections—at different positions along the longitudinal direction. These CAD models are 

presented in Figure 5.
14

Metrolink

Metra

LIRR

NICTD

Figure 5. CAD Representations of Measured Cab Consoles
15

3.3 Baseline Composite Cab Layout

Critical functional, operational, and ergonomic parameters, such as throttle and braking controls, 

instruments, seat position, etc., were reviewed to develop the composite baseline cab. Special 

focus was placed on location, size, and shape of exposed control levers, as well as on surfaces 

likely to pose injury potential during a crash. To develop a composite cab layout amenable to a 

cab occupant protection strategy, the following requirements regarding functionality, safety, 

ergonomics, and overall cab space, were applied:

• All existing functionality shall remain unchanged.

• Any new geometry, instrument, lever, or surface feature introduced shall not interfere 

with safe operation of the equipment.

• Any new geometry, instrument, lever, or surface feature introduced shall not create 

potential for injury during crash.

• Frontal and side vision fields shall not be impacted.

• Control levers, handles, buttons, and knobs shall be within operational reach of 5th

percentile adult female to 95th percentile adult male.

• Cab occupant space shall not be adversely affected.

With the criteria listed above, desk architecture (throttle and brake control levers and panels), 

desk geometry (height, width, and depth), and engineer seat position were selected. These are 

presented in Table 7 and compared with existing cab designs in Figure 6.

Table 7. Proposed Cab Geometry Dimensions

Dimension Value Selected Style Basis Remark

Desk Height 30.0 in LIRR, Metra, NICTD Floor to Desk Top Leading Edge

Desk Depth 24.0 in Metra, NICTD Window Wall to Top Leading 

Edge

Desk Width 41.0 in Metra, Metrolink, NICTD

Desk Console Thickness 2.25 in NICTD Leading Edge Side

Desk Leading Edge to 

Chair Base Column 13.5 in Metra, Metrolink, NICTD Leading Edge Side
16

The selection of these values reflects general practice in the industry for desk geometries. 

However, the location of throttle and brake controllers was chosen to accommodate the need for 

an occupant protection system—most likely to be installed on the desk. The presence and 

location of other items such as radio, console, and footrest, and their selection rationale are listed 

in 

Table 8. The throttle and reverser control was placed right of center to keep the top and under 

desk center free for head, chest, torso, and knee protection system(s). The baseline design did 

not incorporate a footrest or pedal in order to eliminate the potential for foot injury.

Table 8. Cab Equipment

Feature/Item Location Selected Style Basis

Throttle and Reverser Right of Center Metrolink

Brake Control Lever Left of Center Metrolink

Telephone/Radio Cradle Left LIRR, Metrolink, Metra

Overhead Console Yes LIRR, Metra, Metrolink, NICTD

Right Console No LIRR, Metra, Metrolink, NICTD

Left Console Yes LIRR, Metrolink, NICTD

Foot Rest None

Foot Operated Switch Left LIRR, Metrolink, NICTD

0

5

10

15

20

25

30

35

40

Chair Base

Column -

Windshield

Wall

Desk Depth Chair Base

Column - Desk

Edge

Floor-Desk

Height

Torso –

Controller

Clearance

Torso – Desk

Clearance

(Inch)

LIRR

Metra

MetroLink

NICTD

Proposed

Figure 6. Summary of the Reviewed Cab Geometric Dimensions and the Proposed Cab 

Parameters
17

3.4 Summary

Based on a detailed review of four cabs from four different transit agencies, the project team 

developed a baseline cab design that represented a fair composite of the reviewed cabs, provided 

functionality, space, and ergonomics that was similar to the reviewed cabs, and provided 

opportunities for accommodating EPS components.

The baseline cab concept was subsequently developed into a detailed design, suitable for 

fabrication, using appropriate CAD software.

Figure 7. Composite Cab Layout
18

4. Review of Protection Strategies and Standards

To guide the process of developing an EPS, the project team conducted a detailed review of 

literature, standards, and state-of-the-art technologies for occupant protection systems used in the 

automobile, heavy vehicle (bus and truck), and railroad industries.

A key goal of this effort was to understand the approach, strategy, and protection system 

elements used in other industries—particularly, the automobile industry, and to consider the

potential applicability to this cab engineer protection effort. 

Another goal was to review the injury criteria and standards used for occupant protection to 

ensure that we were working towards the appropriate injury index targets in this effort. 

This review is presented in detail in Appendix A. This section summarizes the key findings. 

The protection strategies used in the automotive industry offer elements that can be adapted for

railroad application. Large airbags, similar to those used on the passenger side of automobiles, 

offer good protection for the cab engineer’s head and upper torso under frontal impact. 

Furthermore, the knee airbag or knee bolster type arrangement used for the automobile driver 

positions can also be adapted to protect the cab engineer’s knee against impact forces resulting 

from the unbelted engineer moving against the desk and the knees impacting equipment 

protrusions under the desk. 

Table 9 presents the rail industry standards that were reviewed as part of this effort, and Table 10

presents the automotive and heavy vehicle standards that were reviewed. The review indicated 

that although the impact and crash scenarios, the resulting crash pulses, and the sled test 

requirements for the automobile and railway industry are prescribed differently, the limiting 

injury criteria used are quite comparable.

The review also established that the set of limiting injury indices adopted for this effort was 

reasonable and consistent with other efforts, thereby providing additional confidence in the 

requirements laid out. 
19

Table 9. Summary of the Railway Vehicle Interior Design and Occupant Protection Recommended Practices and Standards

Document Type Description Effective Region/ 

Country

Governing Body

49 CFR PART 238 PASSENGER EQUIPMENT SAFETY STANDARDS USA U.S.-DOT-FRA

49 CFR PART 238.233 S Subpart C – Specific Requirements for Tier I Passenger 

Equipment - Interior Fittings and Surfaces

1999 USA U.S.-DOT-FRA

49 CFR PART 238.435 S Subpart E – Specific Requirements for Tier II Passenger 

Equipment Section - Interior Fittings and Surfaces

1999

49 CFR PART 238.447 S Subpart E – Specific Requirements for Tier II Passenger 

Equipment 

1999

AAR-MSRP Section M -

RP-5104

RP Locomotive Cabs 1974 AAR

AAR-MSRP Section M -

RP-5128

RP Diesel Locomotive Control Stand for New Locomotives 1975

AAR-MSRP Section M -

RP-5132

RP Rounding All Possible Exposed Convex Edges and 

Corners

1971

APTA SS-C&S-011-99 

Rev.1 (3-22-04)

S Standard for Cab Crew Seating Design and Performance 1999 APTA

APTA SS-C&S-016-99 

Rev.1 (3-22-04)

S Standard for Row-to-Row Seating in Commuter Rail 

Cars

2004

APTA SS-C&S-016-99 

Rev.2

S Standard for Passenger Seats in Passenger Rail Cars 2010

EN12663, July 2000 S Structural Requirements for Railway Vehicles 2000 Europe European Committee for 

Standardization

EN15227 Final Draft 2007 S Crashworthiness Requirements of Railway Vehicle 

Bodies

2009 Europe European Committee for 

Standardization

AV/ST9001, Issue One, 

February 2002

S Vehicle Interior Crashworthiness – ATOC Vehicle 

Standard

2002 UK Association of Operating 

Companies

GM/RT2100, Issue One, 

July 1994

S Structural Requirements for Railway Vehicles 1994 Safety & Standards Directorate

GM/RT2100, Issue Four S Requirements for Rail Vehicle Structures 2010 Railway Safety and Standards 

Board

SAF/STD/0057/RSK, 

Version 2.1, Dec. 2004

S Rolling Stock Structural Requirements 2009 Australia Queensland Railway Governance 

and Management Framework

S: Standards, RP: Recommended Practices
20

Table 10. Summary of Automotive Crashworthiness Standards

Document Description Effective Region/ 

Country Governing Body

ECE R-80 Seats of Large Passenger Vehicles 1989, 

2009 (Rev 2) Europe

Economic 

Commission for 

Europe (ECE)

ECE R-29 Protection of the Occupants of the 

Cab of Commercial Vehicles

1993, 

2007 (Rev 1) Europe ECE

ECE R-33 Vehicle Structure in Head-On 

Collision

1995,

2008 (Rev 3) Europe ECE

ECE R-66 Strength of the Superstructure of 

Large Passenger Vehicles

1995,

2008 (Rev 1) Europe ECE

FMVSS 201 Occupant Protection in Interior 

Impact

1968,

Rev. 2008 USA U.S.-DOT

FMVSS 222 Passenger Protection in Commercial 

Vehicles (Used for School Buses)

1968,

Rev. 2008 USA U.S.-DOT

FMVSS 208 Occupant Crash Protection 1977,

Rev. 2008 USA U.S.-DOT

ADR 69

Vehicle Standard (Australian Design 

Rule 69/00 – Full Frontal Impact 

Occupant Protection) 2006 

Compilation 1

2007 Australia Australia DOT and

Regional Services

ISO 3471 Rollover Protection in Construction 

Equipment

1986,

Rev. 2008 Worldwide
21

5. Concept Development

Based on the requirements identified earlier, review of cab configurations, and knowledge of 

strategies employed elsewhere, several concepts to provide occupant protection in impact 

situations were developed. The viability of these various concepts was then evaluated using a set 

of objective criteria; subsequently, top ranked concepts were qualitatively analyzed using the 

appropriate simulation tools. The activities are described in the following subsections.

5.1 Development of Concepts

To initiate the concept development effort, the project team conducted a brainstorming session. 

The brainstorming session included staff from Volpe, Sharma & Associates, and Altair (occupant 

protection system design and simulation experts). The team identified several ideas for occupant 

protection focused on providing protection individually to the head, chest, torso and femur areas. 

Ideas to protect the head included passenger-style airbags, deployable nets, local softening of 

contact surfaces, recessed control levers, drop down bolsters, neck braces, etc. Similarly, chest 

protection ideas included shaping of the console, use of honeycomb, airbags, a desk with an 

energy absorbing longitudinal stroke, knee activated torso bolster, ITS, relocation of controls,

etc. Femur protection ideas included deformable bracket, honeycomb, knee airbags, inflated 

tubular structures, hydraulic dampers, etc. A complete list and associated descriptions for these 

ideas are included in Appendix B. 

Each idea was rated with respect to the following four (4) criteria with a rating of high (H), 

medium (M) or low (L) by each team member:

• Feasibility and acceptability

• Development timeframe

• Likelihood of developing successful design

• Contribution to overall goals (success)

The ideas that were ranked near the top were then paired and combined to develop nine possible 

concepts for the head and chest protection and six ideas for femur protection. These fifteen 

elements were rated using the nine weighted criteria listed in Table 11.
22

Table 11. Evaluation Criteria and Weights for Cab Occupant Protection System Concepts

Weight Criteria Comment

5 Injury Index Reduction Can the concept contribute significantly towards limiting injury 

criteria?

5 Compartmentalization Can the concept help to keep the operator in his/her seat?

5 Affect Egress Does the concept allow reasonable egress?

4 Feasibility Is the concept feasible to develop and implement within the 

time constraints of this project?

3 Simplicity of Design Does it have complex mechanisms or are there many variables 

to control?

3 Maintenance Does the concept increase maintenance time or add new 

inspection requirements?

3 Comfort and

Ergonomics

Is operator comfort or control ergonomics likely to be affected 

by the concept?

1 Weight Concerns Will the concept adversely increase the weight of the cab?

1 Material Costs Are material costs comparable to other concepts?

1 Manufacturing Costs How easily can the system (desk, seat, and protection elements) 

be manufactured?

The weighted score was then used to rank the more viable options. The overall scores and 

ratings are shown in Appendix C and the resulting rankings are listed in Table 12. 

Table 12. Selected Concept Elements for Head, Torso, and Femur Protection

Concept Element Score Rank

Head and Chest

Passenger Style Airbag 1

Passenger Style Airbag + Tethers 2

ITS (Inflatable Tube Structures) 3

Shaping the Console 4

Crushable Console (Honeycomb or Foam) 5

Local Softening 6

Cantilevered Bolster 7

Dropdown Bolster + Shaping the Console 8

Rotating Frame + ITS 9

Femur

Honeycomb or Foam 1

Knee Airbag 2

Deformable Beam Bracket + Honeycomb/Foam 3

ITS 4

Tube in Tube 5

Hydraulic Damper 6
23

To develop the overall protection system, the following three concepts were formulated based on 

the elements listed in Table 12:

• Passenger Style Airbag + Knee Bolster 

• ITS + Knee Airbag (or Knee Bolster)

• Crushable Desk + Crushable Knee Bolster

Analysis of the third concept by the Volpe team using a simplified MADYMO model concluded 

that it was not a viable solution. Based on preliminary simulations, it was not possible to protect 

the head and neck adequately without an airbag. Therefore, subsequent effort was focused on 

the first two concepts. CAD representations of the two concepts are shown in Figure 8 and 

Figure 9.

Figure 8. Occupant Protection System - Concept 1 – Airbag + Knee Bolster

Figure 9. Occupant Protection System - Concept 2 – ITS + Knee Airbag
24

5.2 Preliminary Evaluation of Concept Viability

The intent of these preliminary simulations was to identify the strengths and weakness of the 

concepts, thereby helping to select a configuration for further development and detailed design. 

MADYMO [3] models of the two concepts were developed, including an ATD in the cab seat,

and a desk with the deployable elements. For this initial modeling, typical passenger-style airbag 

and knee bolster properties from an automotive application were used. The initial properties 

were intended to serve as starting points for the analysis, not design targets. The EPS test pulse 

shown in Figure 1 and a 95th percentile adult male ATD were used. A baseline run was made 

with no head, torso, or knee protection system. Several variants of the two concepts were 

investigated, and a detailed description of this preliminary modeling effort is presented in 

Appendix D. The following section highlights the key findings.

5.2.1 Key Results

Injury indices for selected cases are presented in Table 12. Results show that the baseline case 

(no occupant protection system) produces injury indices for head, chest, neck, and femur, which

are significantly higher than the prescribed limits. A quick review of the kinematics shows the 

ATD knees making the first contact below the console resulting in high femur loads, followed by 

the torso and then the head striking the console with significant force.

Several variants of Concept 1 (airbag + knee bolster) yielded positive results, and the target 

injury criteria were met in these cases. Improved performance was observed when airbag 

venting was eliminated to provide better resistance to occupant head travel, reducing the injury 

indices to below 80 percent of the limits. Kinematics show an initial knee hit against the 

deformable knee bolster with nominal femur loads, followed by rotation of the upper torso and 

head about the pelvis, with the head and torso striking the airbag and riding down with low 

acceleration (see appendix D); the moderate HIC values were the result of a late head strike 

against the console. As the design was further developed, better airbag design and deployment 

was implemented, eliminating the head strike, and resulting in improved HIC values (under 200). 

The peak neck injury values, while within limits, were also observed during the late head strike. 

Concept 2 also offered significantly better performance than the base case, with significant 

reductions in injury indices. However, depending on the particular design variation, one or the 

other injury criteria was close to the target limit. Table 12 presents one case (with no vents and 

the ITS units moved back) that showed reasonable injury results. The kinematics generally 

consisted of initial knee contact with nominal femur loads followed by near simultaneous contact 

of the head and torso with the ITS systems with relatively high (but below the limit) HIC and 

chest accelerations. Additionally, it was felt that the kinematics of the ATD were less than ideal, 

due to the rebounding seen after impact.
25

Table 13. MADYMOTM Simulation Results for the Two Concepts and the Baseline

Injury

Response

Require

ments 

95th% 

ATD

Baseline Concept 1 (Airbag + 

Knee Bolster)

Concept 2 (ITS + 

Knee Bolster)

No 

Protection

% of 

Target

W/O Front 

Wall Contact 

and No Vents

% of 

Target No Vents % of Target

HIC_15 700 84,318 12,045

% 531 76% 617 88%

Chest 3ms 

(g) 60.0 75.3 126% 43.3 72% 60.0 100%

V*C (m/s) 1.0 0.44 44% 0.45 45% 0.70 70%

Femur Left 

(N) 10,000 15,556 156% 5,825 58% 6,308 63%

Femur Right 

(N) 10,000 15,554 156% 5,826 58% 6,919 69%

Neck 

Tension (N) 4,170 11,262 270% 2,495 60% 1,210 29%

Neck Comp. 

(N) 4,000 4,509 113% 113 3% 473 12%

Nte 1.00 3.44 344% 0.75 75% 0.62 62%

Ntf 1.00 1.95 195% 0.70 70% 0.43 43%

Nce 1.00 0.27 27% 0.13 13% 0.04 4%

Ncf 1.00 2.15 215% 0.03 3% 0.32 32%

xx Exceeds 100% of requirements

x Exceeds 80% of requirements

5.3 Summary

Two concepts for cab engineer protection were developed using a rigorous process and with 

careful consideration of all parameters. The developed concepts, as well as a baseline (no 

protection) version, were further evaluated using MADYMO simulations.

For the baseline case, the simulations predicted injury indices well in excess of the prescribed 

limits. 

As expected, when compared with the baseline case, both protection concepts showed significant 

improvements for all injury indices. Concept 1 (passenger-style airbag and knee bolster) showed

better performance compared with Concept 2 (ITS with knee bolster), offering better ATD 

kinematics and the potential for all injury indices to be within 80 percent of the limits. For 

Concept 2 (ITS), chest injury index values were close to the limits, in addition to having 
26

unfavorable rebounding kinematics of the occupant due to the lack of energy absorption for the 

upper torso in that concept. Therefore, for this project, Concept 1 was selected for further design 

and development efforts.
27

6. Detailed Design

The EPS identified as Concept 1 (Airbag + Knee Bolster) was then developed in detail, with 

subsequent evaluation and refinement. Upon successful evaluation of the system’s effectiveness, 

the design was documented using engineering drawings. 

The selected concept consisted of two main modules: an automotive passenger-style airbag for 

head and torso protection, and an energy absorbing knee bolster for knee protection. The airbag 

model was derived from an existing passenger-style airbag commonly used in the automotive 

industry, which was enlarged for this application. The energy absorbing knee bolster was 

developed after evaluating several different concepts and iterations for each concept. 

6.1 Airbag System Design

The airbag system is composed of an airbag and an inflator, both of which are housed in a 

standard automotive packaging format. The proposed system uses a relatively large, customdesign airbag similar to an automotive ‘passenger-style’ airbag, and an off-the-shelf inflator 

model # PH-5 from Key Safety Systems (KSS). The airbag cushion is 28 in (700 mm) long and 

18 in (450 mm) wide, with a volume of 5.5 cubic feet (155 liters), and two sets of internal tethers 

to control the desired deployed shape. The airbag dimensions and other key details of the system 

are presented in Figure 10 and Figure 11.

 

Figure 10. Airbag Shape
28

Figure 11. Airbag Module Details
29

Figure 12. Airbag Assembly Components

The airbags are generally triggered by an external trigger control module. On an actual 

automobile (or future railcar application), the trigger module receives input from acceleration 

sensors, and based on the appropriate severity of the sensor input, triggers the deployment of the 

airbag. For a sled test application, the trigger module is contained in the sled test apparatus, and 

is triggered based on a preset Time-To-Fire (TTF). 

On a future rail car application, the expected deceleration pulses under a nominal set of actual 

impact conditions would be reviewed to determine car design-specific TTF characteristics. 

Analytical system performance using a validated model under these nominal crash pulses would 

be used to further refine the TTF design. In the final implementation, TTF can be controlled to 

best suit design intent through either a predefined time following pulse detection, or an 

acceleration magnitude trigger with delay.

The airbag housing is generally constructed of steel (stamped and plated) and houses the airbag 

and the inflator (see Figure 12). The housing is commonly fastened to the vehicle control panel 

at various distributed points. Note that this picture shows an example airbag assembly and that 

the deployment door design will need to be different in its final implementation for the current 

application. Figure 13 provides overall dimensions of the airbag housing.
30

 

Figure 13. Airbag Housing Dimensions

The inflator selected (model: PH-5) is a dual stage model with a pressure rating of 700kPa (101.4 

psi), and a diameter of 45 mm (1.77 in). Figure 14 below shows an image of the PH-5 inflator.

Figure 14. PH-5 Inflator

A dual stage inflator can receive two successive trigger signals to initiate full deployment. In 

certain automotive crash conditions, such as a child being seated facing the airbag, only the first 

of two stages may be triggered. Modern airbag inflators are generally two stage inflators as 

required by recent standards and regulations in the automotive industry. The two stages are 

usually phased 10 milliseconds (ms) apart in a deployment.

Inflators are characterized using an automotive industry standard “Constant Volume Inflation 

Test.” In this test, full flow from the inflator is directed towards a constant control volume 

(pressure vessel) with a volume of 60 liters. The pressure rise in this control volume is 

monitored continuously. The time history of pressure rise in this control volume is the test 

output, which is a measure of the flow rate and capacity of the inflator. Most simulation codes 

take the output of this test as direct input into the airbag module. Off-the-shelf inflators are 

pretested and are supplied with this information by the airbag system suppliers. A standard test 

result for the PH-5 inflator is presented in Figure 15.

11.81 in

5.9 in

4.72 in
31

Figure 15. Output from a 60 Liter Inflation Test – PH5 Inflator

6.2 Knee Bolster Design

Unlike the airbag module, the knee bolster module is not a standardized module. The 

automotive industry uses a combination of deformable metal brackets and deformable plastic or 

composite cover panels on the dashboard. 

To develop the knee bolster design, a detailed finite element (FE) model of the baseline cab 

structure was created in RADIOSS [4], incorporating all relevant details about the desk and 

console. Figure 16 below shows the baseline cab structure FE model used in simulations. The 

force-deflection (F-D) response of the knee bolster module was then derived using a quasi-static, 

nonlinear analysis by applying the load through two knee-form surfaces and calculating the 

displacement response. 
32

Figure 16. Baseline Cab Structure Finite Element Model

The initial target curve for the knee bolster F-D response was the assumed curve used in the 

preliminary MADYMO models, which was based on a typical automotive style knee bolster. 

This served as the initial target not because it was ‘ideal’, but because it had shown reasonable 

performance in the preliminary MADYMO simulations.

To derive a detailed design for the knee bolster, several configurations were simulated in 

RADIOSS and the F-D responses were compared with the assumed target curve. In cases where 

the configuration showed an acceptable match with the target F-D curve, the properties of the 

configuration were transferred to the MADYMO model for a quick assessment of the 

configuration’s efficacy in meeting the injury criteria. This iterative process resulted in a 

promising knee bolster configuration, shown in Figure 17, which matched the target curve 

reasonably well.
33

Figure 17. Force versus Deflection – Preliminary Knee Bolster Design

Preliminary configuration consisted of a honeycomb block working in series with a pair of 

deformable stamped brackets. The system consists of a front plate, honeycomb, back plate, and 

energy absorbing brackets, as shown in Figure 18. For ease of manufacturability and 

prototyping, the deformable brackets were revised to use flat bar stock (3⁄8 in) that provided 

equivalent bending strength. Crushing of the honeycomb in combination with controlled failure 

of the knee bolster brackets provided the desired energy absorption, as well as the appropriate 

ATD kinematics. Figure 18 and Figure 19 highlight the key characteristics and dimensions of 

the final configuration.

0

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400

600

800

1000

1200

1400

1600

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Force (lbf)

Deflection (in)

Proposed Knee Bolster

Target
34

The honeycomb material in the proposed knee bolster system is a HexCel Corporation product 

HexWeb CRIII-3⁄8-5052-0015N-2.3. This model is made up of 3⁄8 in hexagonal cells from 5052 

aluminum with a nominal foil thickness of 0.0015 in and published crush strength of 75 psi. The 

knee bolster brackets are made of ASTM A36 steel with a minimum yield strength of 36 ksi, a 

minimum ultimate strength of 50 ksi, and the dimensions noted in Figure 19. 

Figure 18. Knee Bolster System Assembly (Left)

Deformable Brackets: 

3⁄8 in thick

Back Plate: Steel, 

0.12 in thick

Honeycomb:

Hexcel HexWeb CRIII-

3⁄8-5052-.0015

Front Plate:

Steel, 0.12 in thick
35

Figure 19. Dimensions of Knee Bolster Bracket

6.3 Design Evaluation

The detailed airbag and knee bolster information was then applied to the baseline console to 

prepare a sled test FE model, which included an accurate representation of the desk geometry, 

controls, and protection system. This model included a detailed representation of a 95th

percentile Hybrid III ATD. To simulate a crash scenario, a 23 g crash pulse was imparted to the 

sled model. Forces and displacements of the ATD’s knees, as well as all measurable injury 

indices, were tracked throughout the simulations. Figure 20 shows the full FE model used in the 

simulations.
36

 

Figure 20. Baseline Sled Test Finite Element Model

The airbag cushion was defined as a RADIOSS monitored volume. Two control vents were 

defined to account for fabric permeability, stitching leakage, and actual bag vents. The first vent 

represents the fabric permeability and stitching leakage. A second vent in the airbag model that 

represents actual vents on the airbag was also defined; this vent could be turned ‘on’ or ‘off’ 

depending on the airbag design. Inflator characteristics were defined using the tested and 

published flow curves for the PH-5 inflator.

A RADIOSS 95th percentile Hybrid III deformable dummy FE model for frontal impact was 

positioned into the model. This is a calibrated model that is supplied, under license, by the ATD 

manufacturer, and has been certified by the manufacturer under a variety of test conditions 

including head drop, neck flexion, knee impact, knee slider, and chest impact.

Multiple simulations using different airbag widths and alternate inflator characteristics were 

conducted to fine tune the performance of this system. The airbag widths tried were 400 mm and 

450 mm; while the kinematics and injury indices were similar, the 450 mm bag was selected for 

the final design because it offered better coverage for a wider range of conditions. In addition to 

the standard PH-5 inflator, a theoretical inflator with increased flow capacity (in the ratio of 450 

mm to 400 mm) was tried for the 450 mm bag. As the enhanced capacity inflator did not seem 

to offer any performance benefits, the standard inflator, a pretested, off-the-shelf item, was 

retained for the final design. 

Floor, seat, control modules, and airbag 

container are modeled as rigid bodies.

All other parts are modeled as 

deformable metal sheets 

using shell elements.
37

6.3.1 Simulation Results

The predicted injury indices from the selected design are presented in Table 14. The results 

show that the design was effective in providing the required level of safety. 

Table 14. Injury Indices – Design System (Pre-Characterization) Sled Test Model

Injury Index Parameter Allowable Limit Predicted Injury Index

HIC_15 700 104

Chest 3ms (g) 60 38

Femur Loads 

(N)

Left 10,000 7,611

Right 10,000 7,743

Neck Loads 

(N)

Tension 4,170 2,177

Compression 4,000 934

Neck Injury 

Criteria

Nte 1.0 0.60

Ntf 1.0 0.25

Nce 1.0 0.26

Ncf 1.0 0.26

Figure 21 shows two screen shots of the simulation—one at the beginning and the other at the 

end of maximum excursion of the ATD. The ATD kinematics are as follows: initial contact is 

between the femur and the knee bolster; as the femur loads rise, the torso pitches forward 

slightly, followed by contact between the chest and the airbag, followed almost immediately 

after by contact between the head and the airbag (this being coincident with the rise in neck 

loads). The knees then start straightening out and the head and torso ride down with the airbag. 

The relatively high HIC values seen in the preliminary (MADYMO) analyses were reduced by

effective airbag design and timing that prevented the late head strike seen in the preliminary 

effort, resulting in significantly lower HIC values. Figure 22 provides the time histories of head 

acceleration, femur loads, thorax acceleration, and various neck loads.
38

Figure 21. Designed System (Pre-Characterization) – Simulation Screen Shots
39

Figure 22. Simulation Results – Designed System (Pre-Characterization)

0

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50

Head Acceleration (g)

0 40 80 120 160

Time (ms)

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50

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Chest Acceleration (g)

Time (ms)

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Femur Load (lb)

Time (ms)

Left Femur Load (lbs)

Right Femur Load (lbs)

-200

0

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0 40 80 120 160

Neck Fx (lb)

Time (ms)

Neck-Chest Fx

(lbs)

-300

-100

100

300

500

700

0 40 80 120 160

Neck Fz (lb)

Time (ms)

Neck-Chest Fz (lbs)

Neck-Sup Fz (lbs)

-2000

-1000

0

1000

2000

0 50 100 150 200

Neck My (lb-in)

Time (ms)

Neck-Chest My (lb-in) Neck-Chest My (lb-in)
40

6.4 Weight and Cost

The system is expected to weigh about 30 lb, which is quite reasonable given the safety benefits 

offered. Table 15 below provides a brief breakdown of component weights.

Table 15. Component Weights

Component Weight (lb)*

Airbag Module 9

Knee Bolster (KB) – Brackets (2) 8

KB – Honeycomb 1

KB – Front Plate 3

KB – Back Plate 9

Total 30

*Rounded up to the nearest whole lb

System costs can vary significantly based on order quantities. Based on an annual order quantity 

of 100 units or fewer, the cost of the system is estimated to be around $3,000 per equipped cab. 

A material cost breakdown is provided in Table 16.

Table 16. System Material Costs

Component Cost*

Airbag Module $ 2,500

Knee Bolster (KB) – Brackets (2) $ 100

KB – Honeycomb $ 250

Misc. Fabrication, Sheets, etc. $ 150

Total $ 3,000

*Based on an annual quantity of 100 or fewer

6.5 Summary

The previously chosen concept (passenger-style airbag with a deformable knee bolster) was 

developed into a detailed design. Specifically, airbag details and knee bolster details 

(characteristics) were defined.

Subsequently, this detailed design was developed into a full FE model, and the performance of 

the system was evaluated using RADIOSS under the prescribed EPS Test pulse and a 95th

percentile male ATD.

The results showed that the design was effective in providing the safety benefits expected.
41

7. Component Characterization

To gain confidence in the modeling and simulation results, individual elements of the protection 

system were tested and characterized. The prototype protection system uses two deformable 

subsystems, a ‘passenger-style’ airbag (A/B) and an energy absorbing knee-bolster (K/B) to 

provide the desired level of safety. The goal of this effort was to conduct the tests needed to 

characterize both systems through the deployment and deformation range expected in this 

application.

The following sections describe the tests conducted on the airbag and knee bolster components 

and the subsequent characterization based on those test results. The goal of the testing was not to 

verify whether the individual components met a desired target performance; rather, it was to 

quantify how they performed and then to update the full system analytical model to use those 

tested characteristics. This approach was chosen because performance targets for this effort were 

defined at the system level (injury indices, compartmentalization, etc.) and not at the individual 

component level. In other words, specific pass-fail or other target criteria were not defined at the 

subsystem level, but at the full system level.

7.1 Airbag Characterization

The airbag system is composed of the airbag and the inflator, which are both housed in a 

standard automotive packaging format. The proposed system uses a custom version of an

automotive ‘passenger-style’ airbag and an off-the-shelf inflator (model # PH-5) from Key 

Safety Systems (KSS). Airbag performance can be fully characterized by its deployed shape and 

volume and its leakage under load. The intent of the airbag tests was to develop the shape and 

leakage characteristics, either directly or indirectly. The automotive industry has developed 

standardized test sequences that are used to characterize and quantify these elements. These 

standard tests include the following:

1. Static Deployment Test – characterizes deployed shape and verifies integrity

2. Drop Tower Test – characterizes airbag leakage, and deformation (under load)

7.1.1 Airbag Static Deployment Tests

Two airbag static deployment tests were conducted to establish the airbag’s deployed shape, 

deployment height, and overall bag integrity. These preliminary tests also establish the height of 

the fully deployed airbag (which is a parameter that then flows into the drop tower test setup),

and are used to confirm that the internal tethering works as intended.

Test Input Parameters

The only input parameter for the static deployment test is the time gap between the primary and 

secondary triggers, which was set to 10 ms as per the design of the inflator.

Expected Test Output

• Visual confirmation of deployed shape, including deployed height

• Visual confirmation of airbag integrity
42

Test Sequence

Each specimen airbag was deployed with its paired inflator, with the intended inflation sequence.

Timed electrical signals were sent to the airbag inflator to deploy the bag. The control modules 

for these electrical signals are called squibs. There was no external energy or force applied to the 

bag. The process of inflation, time of inflation, etc. were monitored with high-speed video 

cameras to capture the airbag’s final deployed shape, deployment height, and integrity. Inflation 

pressure was also observed for one bag. Post deflation, the bags were examined for any integrity 

issues, such as tears. Two airbags—one unvented and one vented with two 10 mm diameter 

vents—were tested.

Figure 23 shows the airbag test fixture used for these tests. The triggering system consisted of 

two squibs, with the second one being triggered 10 ms after the first one. Two high-speed video 

cameras were used to record the deployment sequence with a front and a side view. 

Figure 24 shows the inflation sequence of the vented airbag. The results are as follows:

- No cushion integrity issues were observed either during or after the test.

- Cushion kinematics seemed favorable, as seen in Figure 24.

- Tethering worked as intended.

- The deployed height of the airbag was 23 in.

- The deployed shape was as expected.

- There were no anomalies in the pressure signal.

Figure 23. Drop Tower Test Setup
43

Figure 24. Sequence of Airbag Inflation for Static Deployment Test

7.1.2 Airbag Drop Tower Tests

Airbag drop tower tests are conducted to derive the leakage parameters needed to develop input 

for the analytical airbag model. These are ‘indirect tests’ (i.e., the key parameters derived from 

this test, such as leakage and airbag stiffness, are not measured directly). The test sequence is 

modeled using an analytical program such as RADIOSS/MADYMOTM with several known 

parameters (mass, drop height, flow rate into airbag, inflator trigger sequence, etc.) and several 

assumed parameters (fabric leakage, seam leakage, etc.). Post-test, the assumed parameters are 

adjusted so that the measured response (acceleration, velocity, and displacement of the dropping 

mass) matches the model response. 

Test Description

During this test sequence, a known mass was dropped from a defined height onto a fully inflated 

airbag that is triggered and deployed during the test. The mass and the drop height were selected 

based on the energy input needed to adequately characterize the airbag system. The energy 

levels chosen were consistent with the expectations of airbag energy input from prior 

simulations.

Test Input Parameters

The key input to the test is the energy input, which is defined as a product of the weight of the 

drop mass and the height of the drop. The target value of 520 J (minimum) was taken from prior 

MADYMO simulations of a 95th percentile ATD under the EPS test pulse. The test input 

parameters are defined in Table 17. The target energy can be achieved with a 57 in drop height 
44

and an 80-pound mass, if there is no friction in the guide rods. Based on experience, a value of 

66 in was chosen to ensure that the target energy minimum was comfortably met and to account 

for guide rod friction.

Expected Test Output

• Acceleration of the drop mass measured by two accelerometers (0–50 g range)—left and

right on the drop mass 

• Trace of the two ignition (squib) signals for confirmation—one on each squib used to 

ensure that the inflator triggers sequence and timing are correct

• High-speed video of the event using two high-speed video cameras—one side view and 

one oblique view

Test Sequence/Details

A defined mass was dropped from a predetermined height onto a fully inflated airbag that is 

triggered and deployed during the test. The drop tower test fixture consists of mechanisms by 

which a vertically guided impactor with a defined mass can be dropped from a defined height 

onto a fully inflated airbag. Timed electrical signals are sent to the airbag inflator to deploy the 

bag, with the dropping of the mass synchronized with the inflation time of the airbag.

Table 17. Drop Tower Test Parameters

Parameter Value Remarks

Target Energy 

(Minimum)

520 joules (J) Derived from prior MADYMO simulations of the proposed 

concept for a 95th percentile male ATD under the EPS Test 

pulse

Weight of Drop Mass 80 lb Effective weight for 95th percentile male ATD impacting an 

airbag, as determined by previous automotive analyses

Drop Height + Airbag 

Deployed Height

66 in + 23 in

= 89 in

Based on the deployed airbag height established in the Static 

Deployment Test , target energy to be absorbed by the airbag, 

and estimated friction at the guide rods

Data Acquisition 

System Trigger Height

40 in Commensurate with the drop mass speed corresponding to 

the target energy, and timed to capture full event

Trigger Time for 

Primary Squib

45 ms Timed to ensure full inflation

Trigger Time for 

Secondary Squib

55 ms Timed to ensure full inflation
45

Figure 25 and Figure 26 present a schematic and a picture of the drop tower test setup. A total of 

four airbags were tested—two unvented airbags and two vented airbags (each bag with two 10

mm diameter vents).

Figure 26. Airbag Drop Tower Test Frame

Figure 25. Airbag Drop Tower Test Frame
46

Drop Tower Test Results

Measured accelerations, computed forces, velocities, and displacements are presented in Figure 

27 and Figure 28 for the two sets of drop tower tests conducted. Airbag resistive force is 

computed from the known drop mass and its recorded acceleration. Airbag kinematics are 

presented in Figure 29.

The following observations were made:

- No cushion integrity issues were observed either during or after the test.

- No unusual cushion kinematics were observed.

- Acceleration data and calculated velocity seemed reasonable.

- The expected energy input (~ 520 J) was imparted to the bags.

The measured data was used for developing a characterized airbag model.
47

Acceleration (g) versus Time (ms) Velocity (m/sec) versus Time (ms)

Displacement (m) versus Time (ms) Impact Force (N) versus Time (ms)

Force (N) versus Deflection (mm) Kinetic Energy (Nm) versus Time (ms)

Figure 27. Measured and Computed Data – Drop Tower Test #1
48

Acceleration (g) versus Time (ms) Velocity (m/sec) versus Time (ms)

Displacement (m) versus Time (ms) Impact Force (N) versus Time (ms)

Force (N) versus Deflection (mm) Kinetic Energy (Nm) versus Time (ms)

Figure 28. Measured and Computed Data – Drop Tower Test #2
49

Figure 29. Cushion Kinematics – Drop Tower Test Series #2
50

7.1.3 Airbag Model Characterization

The intent of the airbag tests was to use the data to characterize the airbag submodel used in the 

RADIOSS sled test model. Prior to characterizing the data in the RADIOSS model, a 

characterized airbag model was prepared using MADYMO as an intermediate step.

For this effort, a MADYMO model of the drop tower test setup was prepared (see Figure 30). 

All appropriate test parameters (drop height, mass, etc.) and the PH-5 inflator characteristics 

were built into the model. Frictional losses at the guide rod were modeled using a simplified 

damping approach that has historically performed satisfactorily for KSS. Subsequently, airbag 

leakage parameters were adjusted to derive a performance (acceleration profile of the drop mass) 

that was comparable to the test data. Tuning of leakage was accomplished by changing the 

overall permeability factor for the airbag, and by defining an additional discharge function 

representing leakage through the airbag as a function of the internal pressure. Comparative 

results from the characterized MADYMO model and the corresponding test data are shown in 

Figure 31 (for the unvented airbag).

Characterized airbag data from the MADYMO model was transferred to RADIOSS where, with 

RADIOSS-specific adjustments (permeability, discharge, and vent size), the model matched test 

data reasonably well (see Figure 32), though some minor oscillations were noted. To some 

extent these oscillations are seen in the test data as well. The oscillatory behavior seen in the 

RADIOSS drop test simulations are not seen in sled test simulations, as evident in the head, 

chest, and neck acceleration and force data from the post-characterization runs. The differences 

between the MADYMO and RADIOSS models are likely due to minor variations in how 

damping of pressure waves within the airbag is implemented in the two programs, combined 

with the fact that the drop tower simulation has a very ‘mild’ crash pulse (essentially 1 g flat 

forcing function), thereby making the resulting oscillations appear more significant than they are.

In a ‘real’ pulse, where the forcing magnitudes are several times higher, these oscillations, even 

if present, are not likely to have any notable effect on ATD kinematics or resultant injury indices.
51

Figure 30. MADYMO Drop Tower Test Model
52

Time (s)

Figure 31. MADYMO Characterized Data – Unvented Airbag

Displacement (m) Velocity (m/s) Acceleration (g)
53

Time (ms)

Figure 32. Characterization Data – RADIOSS Drop Test Model

Displacement (m) Velocity (m/s) Acceleration (g)
54

7.2 Knee Bolster Testing

The proposed knee bolster K/B assembly consists of two deformable elements: a pair of 

brackets and a honeycomb element. The honeycomb element is sandwiched between the front 

plate (the plate facing the engineer) and the back plate, which is attached to deformable brackets. 

From a simulation perspective, the characteristics of the K/B are defined using the following:

- Traditional material properties of the K/B bracket material—such as the yield strength, 

ultimate strength, and the elongation—in addition to the Young’s modulus, Poisson’s 

ratio, and density

- An aggregate stress-strain curve for the honeycomb material that represents the 

‘engineered’ behavior of the material

Properties such as those defined above are traditionally measured through appropriate quasistatic and material characterization tests. The test procedures and the test results for these 

elements are described in the following sections.

7.2.1 Honeycomb Crush Tests

The intent of this effort was to test the honeycomb material used for the knee bolster system in a 

quasi-static manner in order to characterize its force-deflection characteristics. The test provided

the force-deflection characteristics for input to the RADIOSSTM model of the EPS. The test also 

helped confirm the published crush values of the honeycomb material.

Test Input Parameters

A key input parameter set is the geometry and material of the specimen itself. The specimens 

consist of aluminum honeycomb sheets with a cross-section of a 4 x 4 in square with a height of 

2.5 in. The honeycomb material is model # HexWeb CRIII-3⁄8-5052-0015N-2.3 (made by 

HexCel Corp), and the test specimen is composed of four stacked sheets of 5⁄8 in thickness each. 

The material is composed of 3⁄8 in hexagonal cells made of 5052 aluminum with a nominal foil 

thickness of 0.0015 in, and a published crush strength of 75 psi. 

The other key input parameter is the loading condition; essentially, the test intent is to crush the 

honeycomb material along its loading axis with a quasi-statically applied load until the 

honeycomb is fully crushed (approximately 20 percent of its initial height).

Test Output Parameters

The key output parameters are the time histories of the loading and the crush (displacement) 

from which the F-D curve of the honeycomb material can be established, thereby characterizing 

the honeycomb material.

Test Description

Two specimens of the selected honeycomb sample were tested. Each specimen consisted of four 

4 x 4 in honeycomb pieces cut out from a large sheet and stacked. The stack was backed with

relatively rigid 1⁄8 in thick steel plates on both top and bottom. 

The test frame and loading and instrumentation schematics are shown in Figure 33. The test 

setup consists of a frame, a hand-cranked hydraulic piston, a calibrated load cell, a string-
55

potentiometer for vertical displacement measurement, and a data collection system to record the 

applied load and deflection of the honeycomb specimen.

For each test, the specimen was mounted in the test frame with the hydraulic cylinder just 

touching the top cover plate (see Figure 34). The data collection system and the video recording 

were initiated, and a vertical load was slowly applied by hand cranking the hydraulic pump, with 

the load being continuously monitored on the data collection computer screen. Force and 

deflection data were collected continuously and saved for post-test analysis. The test was 

stopped when a sharp increase in the load was observed, indicating a complete crush of the 

honeycomb.

Honeycomb Test Results

In both tests, the honeycomb specimens crushed in a similar and consistent fashion. Images of a 

crushed test specimen and the four individual crushed pieces are shown in Figure 35. The 

individual pieces show that the honeycomb elements deformed as expected (i.e. the cell shape 

remained with walls buckling in place). 

The crush load-deflection characteristics for both tests are shown in Figure 36. The test curves 

show a load peak before beginning to crush, and then the crushing occurred at a nearly constant 

load. The load peak near the deflection limit occurs as the honeycomb crushes to its solid height. 

In these tests, the stack was 2.5 in tall. The load begins to rise as deflection reaches 2.1 in (84

percent) and rises sharply at 2.25 in (88 percent).

Figure 33. Schematic of the Honeycomb Sample Test Fixture
56

For the honeycomb material used in these tests, the published crush strength is 75 psi with a

+/-15 percent variance—i.e. the sample could provide crush stress between 63.75 and 86.25 psi. 

The two tested cases yield ~65 psi crush stress which is within the manufacturer’s published 

range.

Figure 34. Honeycomb Sample in the Test Frame

Figure 35. Crush Honeycomb Sample (Left) and Individual Layers in Crushed State 

(Right)
57

Figure 36. Crush Force versus Displacement Characteristics for the Honeycomb

Sample
58

Characterization of Honeycomb Model

To ensure that the tested characteristics of the honeycomb were transferred to the FE model 

correctly, a RADIOSS model of the honeycomb block was prepared. The model consisted of a 

honeycomb block with dimensions (4 x 4 x 2.5 in) that reflected the test setup in terms of loading 

conditions, support conditions, and the displacement measurement points. In the simulation, the 

honeycomb block was squeezed between two rigid surfaces, and the F-D curve was extracted.

Figure 37 shows that the response from the characterized honeycomb model was comparable to 

that from the tests. Properties in the secondary directions were taken from published

manufacturer data.

After confirming proper characterization, the properties of the honeycomb block were transferred 

to the full FE sled test model.

Figure 37. Model and Characterization of Honeycomb Block

0

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800

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1200

1400

1600

1800

2000

0 10 20 30 40 50 60

Force (lbf)

Time (ms)

Test

Radioss
59

Knee Bolster Bracket Tests

The intent of this test was to characterize the force-deflection characteristics of the knee bolster 

bracket in a quasi-static manner. The test data was used to characterize a bracket submodel in 

order to provide the basis for input to the RADIOSSTM full FE sled test model of the EPS.

Test Input Parameters

A key input parameter set for the knee bolster bracket is the geometry and material of the bracket 

specimen itself. The knee bolster brackets are made of ASTM A36 steel with a minimum yield 

strength of 36 ksi, a minimum ultimate strength of 50 ksi, and the dimensions noted in Figure 19. 

To confirm the material properties of the specimens, three coupon samples of the material were 

tested by an external laboratory in a standard test that measured the yield and ultimate strengths. 

The measured properties were as follows:

- Yield Point: 51 ksi (minimum); 54 ksi (average)

- Ultimate Stress: 75 ksi (minimum); 78 ksi (average)

- Elongation: 27 % (minimum); 28 % (average)

The other key input parameter is the loading condition; essentially, the intent of the test is to load

the bracket along its loading axis with a quasi-statically applied load through ~ 4 in of deflection.

Test Output Parameters

The key output parameters are the time histories of the loading and displacement from which the 

F-D curve of the bracket can be established.

Test Description

Two bracket specimens were prepared and tested as part of this effort. The specimens were 

tested in the same frame as the honeycomb elements, but with the fixturing modified to suit the 

brackets. The fixture schematic is shown in Figure 38, and the complete setup with the bracket 

mounted in the fixture is shown in Figure 39. The load cell was mounted above the hydraulic 

cylinder and allowed appropriate positioning of the loading point on the bracket. A semicircular 

stock piece was attached to the bottom of the loading piston to minimize friction force at the 

loading interface and to maintain the loading position as the bracket went through relatively large 

displacement. Two string-potentiometers were used to measure the vertical and lateral 

displacements of the bracket at the gusset weld point. The load was applied through a handcranked pump. Load and displacements were measured continuously using a data acquisition 

system connected to the load cell and displacement sensors. Since the bracket experiences 

vertical and lateral deformation, the measurements from the vertical and lateral stringpotentiometers were transformed to compute net vertical and lateral movement under the load 

point. 
60

Figure 38. Schematic of the Knee Bracket Test Fixture

Figure 39. Knee Bracket Sample in the Load Test Frame
61

Bracket Test Results

The tests proceeded as expected and the behavior of the brackets was also as expected. The knee 

bracket was loaded to its peak load in a fairly linear fashion. Once the peak load was reached, 

the load level remained fairly constant, which is ideal behavior. The deformed shape was as 

expected.

The behavior of the two specimens was similar.

Figure 40 shows the final deformed shape of the bracket specimen after load removal.

Figure 41 shows the same specimen before and after the load test. The bracket experienced a 

permanent deformation of 3.75 in in the vertical direction under the load point. Figure 42 shows 

the applied vertical load plotted against the computed vertical displacements for each bracket 

specimen.

Figure 40. Knee Bolster Bracket Specimen – Permanently Deformed 

Under Load

Figure 41. Knee Bolster Bracket Specimen – Pre- and Post-Test Traces
62

Knee Bracket Characterization:

A RADIOSS submodel of the knee bracket was prepared for characterization (see Figure 43).

The model reflected the test setup in terms of loading conditions, support conditions, and 

displacement measurement points. Given that RADIOSS is an explicit solver intended for 

dynamic analysis, the quasi-static nature of the test was simulated by using a loading time of 

1000 ms. Subsequently, the material properties of the bracket (yield and ultimate strengths) were 

adjusted to derive an F-D curve that was comparable to the test data. Two sets of characterized 

data are presented in Figure 44. Data set 1 used a yield strength of 51 ksi and an ultimate 

strength of 75 ksi, mimicking the minimum values seen from the material tests. Data set 2 used a

yield strength of 54 ksi and an ultimate strength of 78 ksi, mimicking the average values seen 

from the material tests. Close correlation is seen between the test data and the submodel data. 

Data set 2 (yield of 54 ksi and ultimate of 78 ksi), being the better match, was used as the final 

characterized set in the full sled model.

7.3 Summary

As part of the effort to better characterize the behavior of the deformable elements of the EPS, a 

series of tests were performed. These included static deployment and dynamic drop tower tests 

on the airbag system, and quasi-static tests of both the knee bracket and the honeycomb material. 

The test results were used to characterize the RADIOSS submodels of the airbag and the knee 

bolster. The post-characterization RADIOSS submodels’ behavior matched the tested behavior 

well.

Knee Bracket Tests - Force Vs Displacement

0

100

200

300

400

500

600

700

800

900

0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00 3.25 3.50 3.75

Displacement (in.)

Force (lbs

Test 1

Test 2

Figure 42. Knee Bolster Bracket Force Deflection Characteristics for the Two 

Specimens
63

Figure 43. RADIOSS Model of Knee Bracket Test Setup

Figure 44. Test and RADIOSS Model Force-Deflection Results for the Knee 

Brackets
64

8. Post-Characterization System Performance

The project team updated the full sled test FE model using the post-test characteristics of 

individual components (see Chapter 7) and simulated a sled test. As part of this effort,

characterized submodels of the airbag and knee bolster were integrated back into the RADIOSS 

model of the sled test, which had been used for prior simulations. The updated model is shown 

in Figure 45, and the key parameters are identified in Table 18. The EPS test pulse was applied 

to the system, with a 95th percentile male ATD positioned in the seat. The model was set up to 

reflect a test in which the sled floor, ATD, and cab environment are all initially at rest and then 

the test pulse is applied to the sled floor, rather than the ATD. Initial results showed that the 

system performed well and that all injury criteria were comfortably met. 

It was also clear that the results could be improved, from both an injury index perspective and 

ATD kinematics perspective, by implementing a small design change. The change involved 

modifying the bottom of the front knee plate by using a hinge connection that would allow the 

bottom to rotate rather than slide (see Figure 45).

Table 18. Final Model Parameters

Airbag

• 700 mm length cushion

• 450 mm width cushion

• PH-5 inflator, 700kPa

• 10 ms time delay between the first and 

second stage trigger

• 155 liters cushion volume

• Upper/lower tether (510/400 mm)

• No vents 

• Updated leakage properties based on 

drop tower test data

Knee Bracket

• L-shaped brackets with gussets – ASTM 

A36, 3⁄8 in thick

• Young’s Modulus: 30.45x106 psi

• Yield Stress: 54 ksi

• Ultimate Stress: 78 ksi

• Elongation: 28 %

Honeycomb

• Crush strength of 65 psi
65

Front plate is 

hinged at

this point.

Figure 45. RADIOSS Model of Engineer Protection System Inclusive of Airbag and 

Knee Bolster Assembly-3-D View and a Sectional Side View
66

8.1 Results

Calculated injury indices from the final model are shown in Table 19, and normalized injury 

indices are shown in Figure 47. As shown, the predicted injury indices are lower than allowable 

limits with a comfortable margin, indicating that the proposed design is successful in meeting the 

design criteria. ATD kinematics from the proposed design are presented in Figure 46 and are 

similar to what was seen in the pre-characterization runs: initial contact is between the femur 

and the knee bolster; the hinged plate design reduced the femur loads and displacements—

without notable detriment to ATD kinematics. As the knee bolster loads rise, the torso pitches 

forward slightly, followed by contact between the chest and the airbag, followed almost 

immediately after by contact between the head and the airbag—this being coincident with the 

rise in neck loads. The knees then start straightening out and the head and torso ride down with 

the airbag, avoiding a head strike and keeping the HIC values low.

Time histories of head acceleration, femur loads, thorax acceleration, chest deflection, chest 

viscous criterion, and neck forces and moments are presented in Appendix E.

Table 19. Performance of the EPS

Injury Parameter Index 

Limit

Calculated Injury Indices (RADIOSS Model)

Base Case Pre-Component 

Characterization Tests

Post-Component 

Characterization Tests

HIC_15 700 9,661 104 87

Chest 3 ms (g) 60 38 38 35

Femur Left (N) 10,000 20,307 7,611 7,318

Femur Right (N) 10,000 20,236 7,743 6,924

Neck Tension (N) 4,170 5,089 2,177 2,504

Neck Compression (N) 4,000 2,525 934 543

Nte 1.0 1.39 0.60 0.77

Ntf 1.0 1.07 0.25 0.29

Nce 1.0 0.28 0.26 0.18

Ncf 1.0 0.82 0.26 0.25
67

Figure 46. ATD Kinematics for the Proposed Design

t = 0 ms t = 20 ms

t = 45 ms t = 70 ms

t = 95 ms t = 120 ms
68

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Allowable Limit

Figure 47. Predicted Normalized Injury Indices for Final Design of Engineer Protection 

System
69

9. Conclusions and Recommendations

This effort has resulted in the development of an EPS that effectively protects a cab engineer in

the event of a moderate train collision (represented by the EPS test pulse, which is a 23 g, 130 

ms trapezoidal crash pulse) and keeps all injury criteria within reasonable limits—without 

requiring input from the engineer, without restraining him or her, and without impeding egress.

The system is expected to add approximately 30 lb to the car weight, which is reasonable, 

considering the safety benefits offered. The cost of such a system is likely to vary significantly 

depending upon volume. For small volumes (100 or fewer units per year), initial estimates of 

material cost indicate that the system is likely to add approximately $3,000 per equipped cab. 

The design was evaluated using a high fidelity, finite element simulation of a sled test, modeled 

upon a representative baseline cab geometry derived from widely used commuter cab styles in 

North American railroads. The model uses a detailed representation of a 95th percentile 

HYBRID III ATD and test-derived characteristics for an airbag and a knee bolster system 

designed to provide crash protection to the cab engineer without the use of seatbelts.

Simulations carried out using this model predict the injury indices to be much lower than 

respective allowable limits; these results provide reasonable confidence for proceeding to the 

next phase of the protection system development. Also, simulation results from various 

intermediate configurations indicate that the resulting injury indices are not overly sensitive to 

minor variations in properties of design elements. In other words, reasonable design flexibility is 

available to achieve the specified injury protection criteria; essentially, the protection system can 

be adjusted to accommodate other considerations, such as ATD categories, car designs, etc.

Following completion of the protection system evaluation, the final configuration was designed 

in detail and documented with engineering drawings. 

In the next phase of the effort, we recommend that the performance of the proposed system be 

verified with a full-scale sled test and model validation. 
70

10. References

1. Code of Federal Regulations, Title 49, Part 571, Section 208, Occupant Crash Protection, 

October 1, 2002.

2. Priante, M. “Review of a Single Car Test of Multilevel Passenger Equipment” American 

Society of Mechanical Engineers, Paper No. JRC2008-63053, April 2008.

3. MADYMO, Version 7.0, TNO Automotive, Delft, The Netherlands.

4. Radioss, Version 10, Altair Hyperworks, Troy Michigan, USA.
A1

APPENDIX A. STRATEGY AND STANDARDS REVIEW

As noted in section 4, this Appendix presents the strategy and standards review that was 

conducted as part of this project. A key goal of this effort was to understand the approach, 

strategy, and protection system elements used in other industries—for example, the automobile 

industry—and to consider their potential applicability to this cab engineer protection effort. 

Sections A.1 and A.2 describe occupant protection strategies used in the automobile and heavy 

vehicle (truck/bus) industries, respectively. Section A.3 discusses how these strategies may be 

applied to the railroad context.

Another goal was to review the injury criteria and standards used for occupant protection to 

ensure that the appropriate index targets were used in this effort. Section A.4 discusses key 

findings from the standards review. Some elements from section 4 are repeated herein, so that 

this appendix can be a complete document by itself.

A.1 AUTOMOTIVE OCCUPANT PROTECTION STRATEGIES

Passenger safety regulations, other industry criteria (for example, the ‘star’ rating system), and a 

competitive marketplace have led automobile manufacturers to develop and deploy advanced 

crash protection strategies that protect automobile occupants in a variety of impact scenarios. 

Although crash protection takes several forms, the focus here is on mitigating injuries from 

secondary contact between the occupant and the vehicle.

A.1.1 Anatomy of a Frontal Crash Event

Automobile frontal crash protection strategies are designed for a standard impact of 35 mph 

against a rigid wall, as shown in Figure A-1. The resulting crash pulse (typical) to which a 

passenger is subjected is shown in Figure A-2. The crash pulse duration for such impacts is in 

the range of 60–80 ms, which is much shorter than the design deceleration pulses used in the 

railroad industry (APTA1 or GM/RT21002 pulses), or the 130 ms pulse used for this effort. 

Upon impact, the automobile structure begins to decelerate almost immediately, but the occupant 

continues to move at the initial velocity of impact until he or she interacts with the vehicle safety 

system or vehicle interior. Once the occupant engages with the safety system/interior, his/her 

velocity is quickly reduced to match the vehicle velocity. The time from first contact of the 

structure with the barrier to the time the occupant reacts to the load varies depending on the 

severity of the impact and the size of the vehicle; however, a typical time range is 30–60 ms. 

 

1

 TA SS-C&S-016-99, Standard for Passenger Seats in Passenger Rail Cars, The American Public Transportation Association, 

Washington, DC.

2 Railway Group Standard GM/RT2100, Requirements for Rail Vehicle Structures, Vol. 4, Rail Safety Standards Board, London, 

UK, December 2010.
A2

Figure A-1. Standard 35 mph Rigid Barrier Impact Test Used by the Automobile Industry

From first contact, the sequence is as follows:

• A crash sensor mounted on the front vehicle rails senses the impact around 2–4 ms. 

• To determine the severity of the impact, that initial pulse is compared to the pulse from a 

secondary crash sensor located in the immediate vicinity of the occupant. This 

measurement and comparison takes approximately 5 to 8 ms. 

• For an impact meeting the severity threshold, the airbags are triggered to deploy around

7–10 ms, and the airbags take 8–15 ms to fully inflate, depending on the inflator volume, 

airbag size, and design pressure. The airbags are fully inflated around 20–25 ms. 

In a frontal crash, the passenger safety protection system applies key loads directly to the 

passenger’s body. Optimization and adjustment of these forces through various restraint systems 

leads to minimization of passenger injury. In general,

• Seatbelts limit the translational motion of the occupant and transfer load to the hips and 

shoulders.

• Head, neck, and chest are decelerated by the primary airbag. 

• Seat ramps (angularity of the seat base from the horizontal) can help transfer loading to 

the pelvis. 

• Contact of the occupant’s knees with the instrument panel or steering column transfers

load onto the occupant’s femurs through the knee bolsters or knee airbags which are 

housed behind the instrument panel or steering column.
A3

Figure A-2. Typical Automobile Crash Pulse Sequencing and Vehicle Response
A4

A.1.2 Relevant Key Elements of an Automotive Protection System

Frontal Airbags

Frontal automotive airbags are designed to provide coverage for frontal as well as oblique frontal 

impacts and are sized to accommodate belted as well as unbelted (i.e., out of position) occupants. 

The driver airbag, which deploys from the steering wheel, is typically round since the actual position 

of the steering wheel during an accident would be unknown and a shaped airbag could not be 

controlled. The passenger airbag is typically rectangular or pillow shaped and may have additional 

protrusions to accommodate different occupant orientations. Both driver and passenger airbags may 

have specific chambers and differential internal pressures to account for multiple impact scenarios.

For unrestrained occupants, airbags significantly reduce injury to the head and chest—compared to 

safety belts alone. Airbags provide a well-proven means of controlling energy absorption for an 

unbelted occupant, which is a critical protective element for survival in a frontal impact. Most 

vehicles have had driver airbags since 1995 and passenger airbags since 1997. Airbag systems are 

constantly being improved, and some of these improvements include the following:

• Sensors and sensor grids that better detect the location, size, and weight of occupants

• Multiple stage airbags that deploy with just enough force for a particular impact and 

occupant 

Knee Airbags

The main function of a knee airbag is to position the body to be more safely accepted by the main 

airbag. The knee airbag also helps to offload some of the impact force from the lap portion of the 

seatbelt which reduces abdomen forces. Knee airbags are designed to protect the occupant’s knee 

and leg area, especially if the occupant is not using a seatbelt. Knee airbags typically inflate like 

normal airbags outside the instrument panel trim, but in some cases the knee airbags inflate beneath 

the trim.

Figure A3. Airbag Protection for an Unbelted Automotive Driver Position 

Occupant
A5

When the driver is unbelted in a vehicle without a knee airbag installed, there is nothing to restrain 

the driver at the initial stage of the collision. The driver’s knees hit the instrument panel and the 

driver moves forward until the knee impacts structure substantial enough to stop the forward 

movement.

A knee airbag can restrain the occupant’s knees at the initial stage of a collision, and this in turn

increases the efficiency of the ride-down effect (ride-down effect describes the coupling of occupant 

velocity with vehicle velocity to maximize secondary impact protection). This coupling essentially

rotates the driver’s upper extremities to face the steering wheel, similar to when the driver is belted,

and this makes possible reductions in both chest deflection and chest acceleration.

Knee Energy Absorbers (Knee Bolsters)

Knee energy absorbers are designed to provide controlled loading of the femur in frontal impact 

scenarios and to limit maximum femur load. These absorbers can consist of specially designed 

brackets with a tailored force versus deflection response and/or special energy absorbing materials. 

Knee bolster performance can affect the kinematics of the occupant—particularly an unbelted one—

and can have a significant effect on the other injury parameters (e.g. head injury criterion).

Knee bolster impact forces may be controlled by adjusting the stiffness of the energy absorbing 

brackets behind the knee bolster and/or modifying the stiffness of the lower trim panel. If the knee 

bolster stiffness is too low, the occupant’s knees will not be restrained and this can contribute to the

submarining of the occupant beneath the instrument panel; in addition, the knees might pass through 

the trim panel and make contact with the instrument panel support beam, which is a very stiff 

member inside most instrument panels, resulting in a very high femur load. If the knee bolster 

stiffness is too high, the femur loads will be too high and this could result in a broken femur or 

pelvis.

Figure A-4. Knee Air Bag Deployment for Knee Injury Protection
A6

Impact Countermeasures

Impact countermeasures are the last line of defense after all other safety system components have 

been exhausted, though they are sometimes employed in combination with existing safety system 

components to soften the interior contact surfaces and reduce the potential for injury. In essence, 

impact countermeasures are soft padding or similar elements used to blunt the force of secondary 

impact. 

A.2 HEAVY VEHICLE OCCUPANT PROTECTION STRATEGIES

Heavy vehicles require different safety strategies due to their mass and high center of gravity. 

Generally, heavy trucks and buses structurally fare better than passenger cars in a crash unless 

impacting a fixed rigid object or another heavy vehicle.

There are no federal requirements for airbags or other advanced safety systems for heavy vehicles. 

Unlike the competitive rating system of the automotive safety standards, heavy vehicles typically 

follow a minimum compliance approach—keeping cost to a minimum—to comply with government 

regulations that do exist. There are, however, a growing number of studies that promote the 

implementation of advanced seatbelt and airbag protection systems in trucks.

Several recent studies3,4,5 have pointed to ejection from the cab and/or crushing of the cab structure 

as the primary reason for serious/fatal injuries observed in truck crashes; ejection was most 

frequently observed in frontal impacts (even at low speeds) and rollovers. Accordingly, a priority 

became retaining the occupant in the cab (prevent ejection). Seatbelts have been shown to be the 

single most important crash protection device for preventing ejection of truck occupants, but airbags 

also help to contain the occupant and prevent ejection.

A.3 APPLICABILITY OF AUTOMOTIVE STRATEGIES TO THE RAILROAD 

ENVIRONMENT

Protection strategies used in the automotive industry offer a number of possibilities for railroad 

application. Unlike the automobile occupant, the railroad cab occupant is unrestrained—current 

regulations, operating procedures, and crew preferences do not allow the use of any seatbelt or like 

restraints for the cab occupant. Furthermore, railroad cab design and construction methods lead to a 

highly confined space with densely populated equipment and limited space for new items. The desk 

layout includes protrusions, i.e., throttle and brake levers/handles that pose a special challenge in 

terms of being kept out of the kinematic path of the cab engineer/occupant. However, the above 

challenges can be addressed with existing protection technology measures, materials, and adaptable 

(software) strategies that are currently being implemented by the automotive industry.

The focus of this program is on frontal impact and injuries. Automotive frontal protection 

techniques provide potential application possibilities. 

 

3 “2006 Large Truck Crash Overview,” Analysis Division of the Federal Motor Carrier Safety Administration, U.S. 

Department of Transportation, Publication No. FMCSA-RI-07-033, December 2007.

4 Craft, R., Blower, D., “The US Large Truck Crash Causation Study,” International Truck and Bus Safety Research and 

Policy Symposium, Knoxville, Tennessee, April 2002.

5 Boyle, L., Meltzer, N., Hitz, J., Knipling, R., “Case-Control Study of Large Truck Crash Risk Factors,” International 

Truck and Bus Safety Research and Policy Symposium, Knoxville, Tennessee, April 2002.
A7

Large airbags—similar to those used on the passenger side of automobiles—offer excellent

protection to a cab engineer’s head and upper torso under frontal impact conditions. Furthermore, 

the knee airbag or knee bolster type arrangement used for automobile driver positions can also be 

adapted to protect the cab engineer’s knee against impact forces resulting from the unbelted engineer 

moving against the desk and the knees impacting equipment protrusions under the desk. 
A8

A.4 REVIEW OF STANDARDS AND INJURY CRITERIA

A detailed review of crashworthiness standards and recommended practices in the automotive, heavy 

vehicle, and railway industries, worldwide, was conducted to better inform the project team, and to 

help define specific goals for the effort. This section presents a list of the documents reviewed and 

the key takeaway points from the review.

A.4.1 Railway Industry Standards

Key standards that referred to operator/occupant protection issues such as injury indices, sled test 

pulses, etc. were the American Public Transportation Association (APTA) standards in the United 

States, the Association of Train Operating Companies (ATOC) standards in the United Kingdom, 

and GM/RT standards in the United Kingdom/Europe. In the United Kingdom, safety of vehicle 

interiors has been controlled by the ATOC standards AV/ST9001, though this standard has been 

superseded by the newly approved GM/RT 2100. Table TA-1 presents the rail industry standards 

that were reviewed.

The sled test crash pulses specified under these standards have taken several forms. Figure A-5 

below presents the crash pulses, or acceleration time histories. Figure A-6 below presents, for 

comparison, the SIV curves that would result from these different pulse definitions.

Figure A-5. Comparison of Crash Pulses
A9

Figure A-6. Comparison of SIV Curves
A10

Table TA-1. Summary of the Railway Vehicle Interior Design and Occupant Protection Recommended Practices and 

Standards

Document Type Description Effective Region/ 

Country

Governing Body

49 CFR PART 238 PASSENGER EQUIPMENT SAFETY STANDARDS USA U.S.-DOT-FRA

49 CFR PART 238.233 S Subpart C – Specific Requirements for Tier I Passenger 

Equipment - Interior fittings and surfaces

1999 USA U.S.-DOT-FRA

49 CFR PART 238.435 S Subpart E – Specific Requirements for Tier II Passenger 

Equipment Section - Interior fittings and surfaces

1999

49 CFR PART 238.447 S Subpart E – Specific Requirements for Tier II Passenger 

Equipment 

1999

AAR-MSRP Section M -

RP-5104

RP Locomotive Cabs 1974 AAR

AAR-MSRP Section M -

RP-5128

RP Diesel Locomotive Control Stand for New Locomotives 1975

AAR-MSRP Section M -

RP-5132

RP Rounding All Possible Exposed Convex Edges and 

Corners

1971

APTA SS-C&S-011-99 

Rev.1 (3-22-04)

S Standard for Cab Crew Seating Design and Performance 1999 APTA

APTA SS-C&S-016-99 

Rev.1 (3-22-04)

S Standard for Row-to-Row Seating in Commuter Rail 

Cars

2004

APTA SS-C&S-016-99 

Rev.2

S Standard for Passenger Seats in Passenger Rail Cars 2010

EN12663, July 2000 S Structural Requirements for Railway Vehicles 2000 Europe European Committee for 

Standardization

EN15227 Final Draft 

2007

S Crashworthiness Requirements of Railway Vehicle 

Bodies

2009 Europe European Committee for 

Standardization

AV/ST9001, Issue One, 

February 2002

S Vehicle Interior Crashworthiness – ATOC Vehicle 

Standard

2002 UK Association of Operating 

Companies

GM/RT2100, Issue One, 

July 1994

S Structural Requirements for Railway Vehicles 1994 Safety & Standards Directorate

GM/RT2100, Issue Four S Requirements for Rail Vehicle Structures 2010 Railway Safety & Standards Board

SAF/STD/0057/RSK,

Version 2.1, Dec. 2004

S Rolling Stock Structural Requirements 2009 Australia Queensland Railway Governance 

& Management Framework

S: Standards, RP: Recommended Practices
A11

The injury indices specified in these documents, while not identical, are reasonably consistent 

and reflect ongoing biomedical research on what the human body can tolerate/survive, as well as

mechanisms for best quantifying/measuring the key parameters. Table TA-2 below presents, for 

comparison, key injury indices from these standards. It should also be noted that injury criteria 

should be selected considering the input crash pulse; for example, some of the tighter injury 

criteria listed in the GM/RT21002 standard are also linked to a softer crash pulse than the APTA 

pulse (note crash pulses plotted in Figure A-5). 

Table TA-2. Comparison of Injury Indices for APTA and GM/RT2100

Body Part Criteria APTA GM/RT 2100

Head HIC15 <700 < 500

3 ms Acceleration < 80g

Neck

Bending in Flexion < 310 Nm

Bending in Extension < 135 Nm

Tension (+Fz) <4,170 N <4,170 N

Compression (-Fz) <4,000 N <4,000 N

Nij <1.0 < 1.0

Femur Axial load <10,000 N < 4,300 N

Knee Displacement < 16 mm

Tibia Index < 0.75

Chest

3 ms Acceleration <60 g <60 g

Deflection < 63 mm

Viscous < 1m/sec

Thoracic Index <1.0

Abdomen Compression < 40 mm

Viscous Criterion <1.0

A.4.2 Automotive and Heavy Vehicle Standards

The project team also reviewed several automotive and heavy vehicle standards as part of this 

effort. A summary of the reviewed standards is included in Table TA-3.

United States injury indices for unbelted automobile drivers and passengers are based on a 50th

percentile adult male for 25 mph (40 km/h) crash into a rigid barrier. The associated test 

procedures and the injury criteria are documented in the Federal Motor Vehicle Safety Standards 

(FMVSS) 208 – Occupant Crash Protection. Criteria for passengers in nonautomobile vehicles,

such as vans and buses, are contained in FMVSS 201 and 222, respectively. Out of these three 

standards, FMVSS 208 has the greatest relevance to rail cab car crash protection since an 

automobile driver, like the cab engineer, is closest to impacting objects.
A12

Table TA-3. Summary of Automotive Crashworthiness Standards

Document Description Effective Region/ 

Country Governing Body

ECE R-80 Seats of Large Passenger Vehicles 1989, 

2009 (Rev 2) Europe

Economic 

Commission for 

Europe (ECE)

ECE R-29 Protection of the Occupants of the 

Cab of Commercial Vehicles

1993, 

2007 (Rev 1) Europe ECE

ECE R-33 Vehicle Structure in Head-On 

Collision

1995,

2008 (Rev 3) Europe ECE

ECE R-66 Strength of the Superstructure of 

Large Passenger Vehicles

1995,

2008 (Rev 1) Europe ECE

FMVSS 201 Occupant Protection in Interior 

Impact

1968,

Rev. 2008 USA U.S.-DOT

FMVSS 222 Passenger Protection in Commercial 

Vehicles (Used for School Buses)

1968,

Rev. 2008 USA U.S.-DOT

FMVSS 208 Occupant Crash Protection 1977,

Rev. 2008 USA U.S.-DOT

ADR 69

Vehicle Standard (Australian Design 

Rule 69/00 – Full Frontal Impact 

Occupant Protection) 2006 

Compilation 1

2007 Australia Australia DOT & 

Regional Services

ISO 3471 Rollover Protection in Construction 

Equipment

1986,

Rev. 2008 Worldwide

European standards ECE R29, R33, R66, and R80 pertain to crashworthiness and passenger 

protection. ECE R-80 includes the sled testing procedures and associated injury criteria. ECE 

R80 does not specify a shape to the sled test pulse, but aims for peak speed of 18.75–20 mph 

(30–32 km/h) with an average acceleration of 6.5–8.5 g. The ECE R80 injury criteria include 

only head, chest, and femur injury indices. The Australian standard ADR 69/00 specifies a 48 

km/h rigid barrier impact test for motorized vehicles and defines required injury indices for head, 

neck, chest, and femur.

For comparative purposes, a summary of the automotive industry injury criteria from FMVSS 

208, ECE R80, and ADR 69/00 is included in Table TA-4.

The HIC, chest, and femur injury criteria used in the automobile industry across the world are 

similar, perhaps underscoring the globalization of the automotive market. The European 

standards ECE R80 do not include any neck injury criterion. 
A13

Table TA-4. Summary of Automotive Injury Criteria

Body Part Criteria FMVSS 208 ECE R80 ADR69/00

Head

No Head 

Contact

HIC15 <700 <500 <700

HIC36 <1000

3 ms 

Acceleration

<75 g

Neck

Tension <937 lbf

(4,170 N)

<3,300 N

Compression <899 lbf

(4,000 N)

Nij <1.0

Femur

Axial load <2,250 lbf 

(10,000 N)

<10,000 N

<8,000 N (20

ms)

<10,000 N <10,000 N

Chest

3 ms 

Acceleration

<60 g <60 g <60 g

Deflection <63 mm <76.2 mm <76.2 mm

A.4.3 Injury Index Summary

Although the impact and crash scenarios, resulting crash pulses, and sled test requirements 

between the automobile and railway environments—as well as within the railway industry—

differ significantly, the injury criteria used are quite similar. This fact confirms that regulatory 

identities around the world are adopting reasonably consistent standards; it also establishes that 

the set of limiting injury indices adopted for this effort was reasonable and consistent with other 

efforts, thereby providing additional confidence in the requirements laid out.
A14

APPENDIX B. BRAINSTORM SESSION TO GENERATE CONCEPTS FOR THE PROTECTION SYSTEM

Table TB-1. Concepts for Head Area

No. Component/ 

Technique Description

Acc

Feasibility + 

eptability

Development 

Timeframe

Likelihood of 

Success

Comment

1 Passenger Style Airbag Large airbag using desk top surface 

and console surface for reaction loads High Short High

Will also be helpful in torso 

protection (may have 

multiple chambers to control 

shape)

2 Deployable Net Deploy from top, sides or bottom Medium Long Medium

Based on pyrotechnic (pyro) 

deployment (a controlled 

explosion/inflation used for 

positioning a device)

3 Local Softening

HIC Cartridge concept; localized 

application of energy absorbing 

material(s)

High Short High

May not be effective if 

ATD/Engineer does not 

impact the surface

4 Friendly Controls

Breakaway or compliant controls that 

move away from the operation during 

impact

Medium Long High

May not be effective if 

ATD/Engineer does not 

impact the surface

5 Recessed Controls Low Short High

6 Dropdown Bolster Swung down from ceiling to arrest 

upper body High Medium MediumHigh

Hinged and deployed using 

pyro; from the ceiling

7 Cantilevered Bolster Swung from either side High Medium MediumHigh

8 Neck Brace Low Short High
A15

Table TB-2. Concepts for Torso Area

No. Component/ 

Technique Description

Acceptability

Feasibility + 

Development 

Timeframe

Likelihood of 

Success

Comment

1 Shaping the Console Contoured shape + variable crush 

behavior High Short High

2 Honeycomb or 

Foam Applied at the desk edge High Short Small

3 Airbag for Torso Designed to engage torso + pelvis only High Short Small

4 Extended Desk

Extend desk edge to be permanently 

closer to the operator’s torso when the 

operator is in the normal operating 

position; will most likely require the 

operator to push back/rotate the chair to 

get out of the chair

Medium Short Small Highly feasible if it does not 

impede operator egress

5 Stroking Desk

Energy absorption elements behind the 

desk; entire desk moves forward and 

away from the operator during impact

Medium Medium Small

6 Inclined Seat Seat pan and back tilted back slightly Medium Short Small

Needs Human Factors input, 

AAR MSRP S-5104 requires 

3–6 degree tilt back of the 

seat pan and 95–115 degree 

tilt back of the seat back

7 Rotating Seat Base

Mechanism in the seat base to allow the 

seat pan and back to rotate up (pitch 

backward) during impact

Medium Long Medium

8 Seat Base Plastic 

Deformation

Rear side of seat base collapses to 

allow the seat to pitch backwards during 

impact

Medium Medium MediumHigh
A16

No. Component/ 

Technique Description

Acceptability

Feasibility + 

Development 

Timeframe

Likelihood of 

Success

Comment

9 Knee Activated 

Torso Bolster

Knee pushes the knee bolster plate 

which is hinged to the torso bolster and 

in turn pushes the torso bolster up to 

engage operator torso

Medium Long Medium

Torso bolster will be part of 

the desktop surface in normal 

usage.

10

Movable Controls 

and Under-Desk 

Devices

Controls and under-desk devices are 

mounted in rails; they move forward 

and away from the operator during 

impact

Medium Medium High

11 Deployable 

Seatbelts Low Long Low

12

Concept No. 1 + 

Inflatable Tube 

Structure (ITS, 

Braided Tube)

High Medium High

13 ITS + Sidewall 

Tethers High Medium High

14 Rotating Frame + 

Net High Medium High

Frame hinged at the floor;

needs pyro; how would the 

net deploy?

15 Rotating Frame + 

ITS High Medium High

Frame hinged at the floor;

needs pyro; ITS will be part 

of the desk edge

16 Dynamically 

Extending Desk

Move desk edge closer to engineer 

using pyro High Medium High

Desk edge could be shaped 

dynamically to provide larger 

reaction area

17 Deploying ITS from 

Desk Mounted Arms

High Medium High

Arms swing up from the 

desk; hinged at the front desk 

edge?

18 Relocating Controls Medium Short High Need Human Factors input
A17

Table TB-3. Concepts for Femur Area

No. Component/ 

Technique Description

Acceptability

Feasibility + 

Development 

Timeframe

Likelihood of 

Success

Comment

1 Beam/Bracket + 

Honeycomb

Knee bolster backed by a deformable 

beam/bracket and crushable honeycomb High Short High

2 Hydraulic Damper Knee bolster backed by rotary or linear 

damper High ShortMedium High

3 Honeycomb Only High Short High

4 Knee Airbag Deployed in front of or behind the knee 

panel High Medium High

5 Inflatable 

Tube/Braided Tube

Generally known as Inflatable Tube 

Structures (ITS) High Medium High

6 Buckling/Deforming 

Structures

Structures designed to take plastic 

deformation during impact High Short High

7 Tube in 

Tube/Cutting Head

Concentric, telescoping tubes in which 

the inner tube has a cutting edge that 

tears the outer tube during the stroke to 

absorb energy

High Medium Medium

8 Structural Foam High Short High
A18

APPENDIX C. EVALUATION OF POTENTIAL CONCEPTS FOR THE PROTECTION SYSTEM

Table TC-1. Evaluation of Concepts for Head and Torso Protection

No. Concept Description

Injury Index ReductionCompartmentalizationAffect EgressDevelopment TimeframeSimplicity of DesignMaintenanceComfort & ErgonomicsWeight ConcernsMaterial CostsManufacturing Costs

Weighting Factor 5.0 5.0 5.0 4.0 3.0 3.0 3.0 1.0 1.0 1.0 SUM

1 Passenger Style Airbag 4.75 4.50 4.50 3.88 3.63 4.25 4.50 4.25 3.50 3.50 133

2 Shaping the Console 2.75 3.50 4.25 4.25 4.25 4.75 4.25 4.63 4.38 4.25 123

3 Local Softening 2.63 1.50 4.88 4.13 4.50 4.50 4.75 4.75 3.88 3.88 115

4 ITS 3.88 4.00 3.88 3.38 3.25 4.00 4.63 4.13 3.13 3.25 118

5 Passenger Style Airbag + Tethers 4.88 4.88 3.75 3.50 3.00 3.88 4.50 4.25 3.25 3.25 126

6 Crushable Console (Honeycomb or Foam) 3.38 3.38 4.25 4.00 4.25 4.25 4.50 4.50 3.38 3.50 121

7 Dropdown Bolster + Shaping the Console 3.88 4.25 3.50 3.13 2.75 3.25 4.38 3.25 3.38 3.13 112

8 Cantilevered Bolster 3.50 3.75 3.88 3.13 3.25 3.50 4.38 3.50 3.38 3.50 112

9 Rotating Frame + ITS 4.00 4.25 3.13 2.75 2.75 3.13 4.25 3.00 2.88 2.88 107
A19

Table TC-2. Evaluation of Concepts for Femur Protection

No. Concept Description

Injury Index ReductionCompartmentalizationAffect EgressDevelopment TimeframeSimplicity of DesignMaintenanceComfort & ErgonomicsWeight ConcernsMaterial CostsManufacturing Costs

Weighting Factor 5.0 5.0 5.0 4.0 3.0 3.0 3.0 1.0 1.0 1.0 SUM

1 Honeycomb or Foam 3.88 3.88 4.88 4.50 4.63 4.50 4.38 4.50 4.13 4.25 135

2 ITS 4.25 3.75 4.63 3.50 3.50 4.00 4.75 4.00 3.38 3.38 125

3 Knee Airbag 4.75 4.63 4.63 3.63 3.88 4.00 4.75 4.13 3.25 3.38 133

4 Hydraulic Damper 3.50 3.75 4.50 3.50 3.88 3.50 4.13 3.75 3.38 3.50 118

5 Tube in Tube 3.63 4.00 4.50 3.38 3.75 4.00 4.25 3.88 3.88 3.75 122

6 Deformable Beam Bracket + Honeycomb/Foam 4.38 4.38 4.50 4.00 4.13 4.38 4.25 4.25 4.00 4.00 133
A20

APPENDIX D. PRELIMINARY EVALUATION OF CONCEPT VIABILITY

Prior project effort generated the following two promising concepts for an Engineer Protection 

System (EPS):

1. Automotive passenger-style airbag with a crushable knee bolster

2. ITS with a knee airbag or crushable knee bolster

The intent of the preliminary simulations described herein was to identify the strengths and 

weakness of the two concepts, thereby helping to select a configuration for further development 

and detailed design. MADYMOTM models of the two concepts were developed, including the 

ATD in cab seat and a desk with the deployable elements. For this initial modeling, typical 

passenger style airbag and knee bolster properties from an automotive application were used. 

The initial properties were intended to serve as starting points for the analysis, not design targets. 

The EPS test pulse shown in Figure 1 (main body) and a 95th percentile adult male ATD were 

used. A baseline run was made with no head, torso, or knee protection system.

Several variants of the two concepts were investigated, including airbags and ITS with different 

venting characteristics, multiple cab front wall configurations, etc. Concept 2 was evaluated 

with both knee airbag and knee bolster configurations. The airbag, knee bolster, ITS, and knee 

airbag characteristics used in the two concepts are shown in Figures D-1 through D-4. The 

investigated scenarios are summarized in Table TD-1.

For both concepts, injury indices for head, chest, neck, and femur were computed and are shown 

in Table TD-2 and Table TD-3. Also shown in those tables are injury indices for the baseline 

case (i.e., no protection system).

Figure D-1. Airbag Model Characteristics for Concept 1
A21

0

200

400

600

800

1000

1200

1400

0 1 2 3 4 5

Force (lbf)

Displacement (in)

Figure D-2. Knee Bolster Force-Deflection Characteristics Assumed for Concept 1 

Figure D-3. Inflatable Tubular Structure (ITS) characteristics for Concept 2

Figure D-4. Knee Airbag Characteristics for Concept 2
A22

Table TD-1. Investigation Scenarios for Concepts 1 and 2

Item 

# Model Airbag Front Wall

Airbag 

Vent

Knee 

Bolster ITS Knee Airbag ITS Vent ITS Location Restraint Spec

1 Baseline

No Protection N/A

2

Concept 1

Y Y 2x20mm Y

N/A

Airbag:

630D fabric

400mm width

Upper/lower tethers

(510/400mm)

140 liters volume

PH5 inflator

TTF: 15 ms

3 Y N 2x20mm Y

4 Y N 2x10mm Y

5 Y N No vents Y

6

Concept 2 N/A

N Y Y No vents

Base Location

ITS Configuration:

7” diameter

700 mm length

15 liters volume

CGI-200 inflator

No vents

TTF: 15 ms

KAB Configuration:

20 liters volume

CGI-260 inflator

No vents

TTF: 15 ms

7 Y Y N No vents

8 Y Y N 2x10mm

9 Y Y N 2x20mm

10 Y Y N No vents Moved 4” back

11 Y Y N 2x10mm

12 Y Y N 2x20mm
A23

Table TD-2. MADYMOTM Simulation Results for Concept 1 and Baseline

Injury

Response

Require

ments 

95th% 

ATD

Baseline Concept 1 System (Airbag + Knee Bolster)

No 

Protection %

W/ Front 

Wall 

Contact & 

2x20 mm 

Vents

%

W/O Front 

Wall Contact 

& 2x20 mm 

Vents

%

W/O Front 

Wall Contact 

& 2x10 mm 

Vents

%

W/O Front 

Wall Contact 

& No Vents

%

HIC_15 700 84,318 12,045% 433 62% 1,215 174% 625 89% 531 76%

Chest 3 ms 

(g) 60.0 75.3 126% 41.2 69% 41.2 69% 38.4 74% 43.3 72%

V*C (m/s) 1.0 0.44 44% 0.39 39% 0.39 39% 0.47 47% 0.45 45%

Femur Left 

(N) 10,000 15,556 156% 5,825 58% 5,825 58% 5,825 58% 5,825 58%

Femur Right 

(N) 10,000 15,554 156% 5,826 58% 5,826 58% 5,826 58% 5,826 58%

Neck 

Tension (N) 4,170 11,262 270% 2,495 60% 4,434 106% 2,953 71% 2,495 60%

Neck Comp. 

(N) 4,000 4,509 113% 113 3% 113 3% 113 3% 113 3%

Nte 1.00 3.44 344% 0.72 72% 0.72 72% 0.52 52% 0.75 75%

Ntf 1.00 1.95 195% 0.65 65% 1.16 116% 0.56 56% 0.70 70%

Nce 1.00 0.27 27% 0.11 11% 0.00 0% 0.10 10% 0.13 13%

Ncf 1.00 2.15 215% 0.03 3% 0.03 3% 0.03 3% 0.03 3%

xx Exceeds design requirements

x Exceeds target (80 % of design requirements)
A24

Table TD-3. MADYMOTM Simulation Results for Concept 2 and Baseline

Injury

Response

Requir

ements 

95th% 

ATD

Baseline Concept 2 System

ITS + Knee

Airbag

ITS + Knee Bolster ITS (Moved Back 4 Inch) + Knee Bolster

No 

Prot. % No Vents % No Vents %

2 x 10

mm

Vents

%

2 x 20

mm

Vents

% No 

Vents %

2 x 10

mm

Vents

%

2 x 20

mm

Vents

%

HIC_15 700 84,318 12,045% 275 39% 302 43% 305 44% 298 43% 617 88% 654 93% 917 131%

Chest 3 ms 

(g) 60.0 75.3 126% 62.6 104% 56.0 93% 55.7 93% 55.8 93% 60.0 100% 60.4 101% 58.7 98%

V*C (m/s) 1.0 0.44 44% 0.74 74% 0.62 62% 0.63 63% 0.65 65% 0.70 70% 0.69 69% 0.67 67%

Femur Left 

(N) 10,000 15,556 156% 18,015 180% 8,504 85% 8,334 83% 7,902 79% 6,308 63% 6,157 62% 5,858 59%

Femur Right 

(N) 10,000 15,554 156% 17,939 179% 9,055 91% 8,808 88% 8,318 83% 6,919 69% 6,751 68% 5,854 59%

Neck 

Tension (N) 4,170 11,262 270% 2,426 58% 2193 53% 1,911 46% 4,341 104% 1,210 29% 1,206 29% 1,693 41%

Neck Comp. 

(N) 4,000 4,509 113% 118 3% 115 3% 114 3% 239 6% 473 12% 465 12% 278 7%

Nte 1.00 3.44 344% 0.53 53% 0.74 74% 0.54 54% 1.26 126% 0.62 62% 0.85 85% 0.53 53%

Ntf 1.00 1.95 195% 0.78 78% 0.62 62% 0.56 56% 0.73 73% 0.43 43% 0.33 33% 0.41 41%

Nce 1.00 0.27 27% 0.01 1% 0.00 0% 0.00 0% 0.00 0% 0.04 4% 0.00 0% 0.14 14%

Ncf 1.00 2.15 215% 0.05 5% 0.03 3% 0.03 3% 0.39 39% 0.32 32% 0.27 27% 0.32 32%

xx Exceeds design requirements

x Exceeds target (80 % of design requirements)
A25

The results showed that the baseline case (no occupant protection system) produces injury 

indices for head, chest, neck, and femur, which are significantly greater than the requirements. 

Concept 1 (airbag +knee bolster) generally met the specified criteria, except for the case where 2

x 20 mm vents were used and there was no front wall ahead of the airbag. Such a condition 

allows the inflated bag to move away from the occupant, thus reducing the overall resistance the 

airbag would offer against forward/downward acceleration of occupant’s upper body (i.e. the 

head and chest). Normalized injury index plots for Concept 1 simulations are shown in Figure D5.

When the front wall was introduced to constrain airbag expansion longitudinally, or if airbag 

venting was eliminated, the airbag provided improved resistance to occupant head travel. The 

kinematics show an initial knee hit against the deformable knee bolster with nominal femur 

loads, followed by pitching of the upper torso and head about the pelvis, with the head and torso 

striking the airbag and riding down with it with low acceleration; the moderate HIC values were 

the result of a late head strike against the console (see figure D-6). As the design was further 

developed, improved airbag design and deployment was implemented, eliminating the head 

strike, and resulting in improved HIC values (under 200). The peak neck injury values, while 

within limits, were also observed during the late head strike. 

Normalized Injury Values for 95th Occupant Simulation - Concept 1

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

HIC_36 HIC_15 Chest

3ms (g)

V*C

(m/s)

Femur

Left (N)

Femur

Right (N)

Neck

Tension

(N)

Neck

Comp.

(N)

Nte Ntf Nce

No Protection

W/Front Wall Contact_V 2X20mm

W/O Wall Contact_V 2X20mm

W/O Wall ContactV 2X10mm

W/O Wall Conatct_ No Vent Design Requirement

Design Target

Normalized Injury Values for 95th Occupant Simulation - Concept 1

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

HIC_36 HIC_15 Chest

3ms (g)

V*C

(m/s)

Femur

Left (N)

Femur

Right (N)

Neck

Tension

(N)

Neck

Comp.

(N)

Nte Ntf Nce

No Protection

W/Front Wall Contact_V 2X20mm

W/O Wall Contact_V 2X20mm

W/O Wall ContactV 2X10mm

W/O Wall Conatct_ No Vent Design Requirement

Design Target

Figure D-5. Normalized Required and Design Target Injury Indices for Concept 1 

Configurations
A26

@150ms

@70ms

@30ms

Figure D-6. ATD Kinematics for Baseline, Concept 1 with Front Wall and 20 mm 

Vents, and Concept 1 without Front Wall and without Vents Configurations @ 30

ms, 70 ms, and 150 ms of Crash Initiation
A27

Results for Concept 2 for the various configurations are shown in Table TD-3 and the 

normalized injury indices plots are shown in Figure D-7. From an injury index perspective, 

Concept 2 performed reasonably well, with the following observations:

• When knee airbags were used, chest acceleration and femur load criteria were exceeded. 

• With the knee bolster and the ITS positioned close to the occupant, neck injury criteria

were somewhat elevated.

• With the ITS moved back, and with the knee bolster, the HIC values approached or 

exceeded the limit, and the chest injury criteria were also high.

The kinematics generally consisted of initial knee contact with nominal femur loads followed by 

near simultaneous contact of the head and torso with the ITS systems with relatively high (but 

below the limit) HIC and chest accelerations (see figure D-8). It was felt that the kinematics of 

the ATD were less than ideal due to the post-impact rebounding observed. 

Normalized Injury Values for 95th Occupant Simulation - Concept 2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

HIC_36HIC_15

Chest 3ms (g)

V*C (m/s)

Femur Left (N)

Femur Right (N)

Neck Tension (N)

Neck Comp. (N)

Nte

Ntf

Nce

ITS+KAB_No Vent

ITS+K/B_No Vent

ITS+K/B_V2X10mm

ITS+K/B_V2X20mm

Mod ITS+K/B_No Vent

Mod ITS+K/B_V2X10mm

Mod ITS+K/B_V2X20mm

Design Requirement

Design Target

Normalized Injury Values for 95th Occupant Simulation - Concept 2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

HIC_36HIC_15

Chest 3ms (g)

V*C (m/s)

Femur Left (N)

Femur Right (N)

Neck Tension (N)

Neck Comp. (N)

Nte

Ntf

Nce

ITS+KAB_No Vent

ITS+K/B_No Vent

ITS+K/B_V2X10mm

ITS+K/B_V2X20mm

Mod ITS+K/B_No Vent

Mod ITS+K/B_V2X10mm

Mod ITS+K/B_V2X20mm

Design Requirement

Design Target

Figure D-7. Normalized Required and Design Target Injury Indices for Concept 2 

Configurations
A28

@30ms

@70ms

@130ms

Figure D-8. ATD Kinematics for Concept 2 Configurations: Knee Airbag without 

Vents; Knee Airbag without Vents with ITS Moved Back by 4 in at 30 ms, 70 ms, 

and 130 ms After Crash Initiation
A29

SUMMARY

Two concepts for cab engineer protection were developed using a rigorous process and with 

careful consideration of all design envelope and injury parameters. The developed concepts, as 

well as a baseline (no protection) version, were further evaluated using MADYMOTM

simulations.

For the baseline case, the simulations predicted injury indices well in excess of the prescribed 

limits. 

As expected, both protection concepts considered showed significant improvements for all injury 

indices compared with the baseline case. Concept 1 (passenger side airbag and knee bolster) 

showed better performance compared with Concept 2 (ITS with knee bolster), offering better 

ATD kinematics and the potential for all injury indices to be within 80 percent of the limits. For 

Concept 2 (ITS), chest injury index values were close to the limits, in addition to exhibiting

unfavorable rebounding kinematics for the occupant due to the lack of upper torso energy 

absorption. Therefore, for this project, Concept 1 was selected for further design and 

development efforts.
A30

APPENDIX E. Injury Index Plots – Final Run

Figure E-1. Head Acceleration Time History

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

50.00

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 160.00

Head Acceleration (g)

Time (ms)
A31

Figure E-2. Femur Loads Time History

Figure E-3. Thorax Acceleration Time History

0

500

1000

1500

2000

2500

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 160.00

Femur Loads (lbf)

Time (ms)

Left Femur (lbf)

Right Femur (lbf)

Femur Load Limit (lbf)

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

0.00 50.00 100.00 150.00 200.00 250.00 300.00 350.00

Thorax Acceleration (g)

Time (ms)
A32

Figure E-4. Knee Bracket - Load versus Displacement

Figure E-5. Neck Fx Loads Time History

0

500

1000

1500

2000

2500

0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00

Femur Loads (lbf)

Knee Bolster Displacement (in)

Left Femur Load (lbf)

Right Femur Load (lbf)

-100

-50

0

50

100

150

200

250

300

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 160.00

Neck Fx Loads (lbf)

Time (ms)

Neck-Sup Fx (lbf)
A33

Figure E-6. Neck Fz Loads Time History

Figure E-7. Neck Moments Time History

-200

-100

0

100

200

300

400

500

600

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 160.00

Neck Fz Loads (lbf)

Time (ms)

Neck-Sup Fz (lbf)

Neck-Chest Fz (lbf)

-150

-100

-50

0

50

100

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 160.00

Neck Moments (lbf-ft)

Time (ms)

Neck-Sup My (lbf-ft)

Neck-Chest My (lbf-ft)
A34

Figure E-8. Thorax Acceleration Time History

Figure E-9. Chest Viscous Criterion Time History

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

0.00 50.00 100.00 150.00 200.00 250.00 300.00 350.00

Thorax Acceleration (g)

Time (ms)

-0.30

-0.20

-0.10

0.00

0.10

0.20

0.30

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 160.00

Chest Viscous Criterion (m/s)

Time (ms)
A35

Figure E-10. Neck Injury Criteria (Nij) Summary

-200

-100

0

100

200

300

400

500

600

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 160.00

Neck Loads (lbf) and Neck Moment 

(lbf-ft)

Time (ms)

Neck-Sup Fx (lbf)

Neck-Sup Fz (lbf)

Nte = 0.769583 Neck-Sup My (lbf-ft)

Ntf = 0.290492

Nce = 0.177359

Ncf = 0.253288