analyzing roadside safety implications of future vehicle

1 Copyright © 2014 by ASME

ANALYZING ROADSIDE SAFETY IMPLICATIONS OF FUTURE VEHICLE DESIGNS

Tejas Ruparel National Crash Analysis Center George Washington University

Washington, DC, USA [email protected]

Karma Yonten National Crash Analysis Center George Washington University


Azim Eskandarian National Crash Analysis Center George Washington University


ABSTRACT To meet new Corporate Average Fuel Economy (CAFE)

standards, future vehicles are expected to be more

environmentally friendly and fuel efficient. In addition to

introducing innovative manufacturing methods and structural

modifications, automobile manufacturers are primarily adopting

lightweighting technologies to meet the demands for more fuel

efficient vehicles. It is seen from prior research that by focusing

on lightweight (LW) designs alone, the average new vehicle

could weigh 28% less in 2016 than it does today. Using LW

designs is not without its challenges though. These designs

represent significantly different dynamic characteristics and

crashworthiness response when compared against original

designs. Accordingly, it is necessary to evaluate the safety

implications of these LW vehicles under impact scenarios with

various roadside infrastructures. It is also necessary to ensure

that the existing infrastructure can satisfy required safety

standards in protecting the occupants under different crash

conditions.

In this paper, we adopt Finite Element Method (FEM) for

modeling and simulating different crash scenarios in order to

evaluate the safety implications of future LW vehicle designs.

Baseline (BL) models for three vehicles – Toyota Yaris, Ford

Taurus and Chevy Silverado are appropriately LW modeled

with 15% (LW15) and 25% (LW25) reduction in weight, whilst

maintaining structural stiffness and Center of Gravity.

Numerical simulations are then performed for a 25° impact

angle against three common roadside infrastructures – Concrete

median barrier, Strong post W-beam guardrail and W-beam

transition barrier at three different speeds – 50, 70 and 100

km/hr. The goal is to conduct a matrix of simulations in order to

provide comprehensive and relative safety assessment. Barrier

performance is then gauged in accordance to the MASH

(Manual for Assessing Safety Hardware) [1] criteria wherein the

metrics take into account evaluation factors such as structural

adequacy and occupant risk.

INTRODUCTION For several years, government agencies, automotive

industries and researchers have collectively undertaken a

variety of efforts to increase roadside safety. One of such tasks

is the crash testing of roadside hardware and infrastructure in

order to assess its safety performance when impacted by errant

vehicles. In the early 20th

century, state highway agencies

designed and tested their hardware under the procedures and

criteria’s they developed. Although this approach helped

identify effective roadside hardware, the methods and criteria’s

used distinctly varied from state to state and hence lacked

information sharing for consistent performance assessment. The

first de facto national standard for crash testing was published

in the Highway Research Correlation Service Circular 482 in

the year 1962. It accounted for and classified most common

cars and accordingly set standards for impact speeds, angle of

approach and evaluation criteria’s. Ever since, the protocols on

how to perform crash tests have evolved from National

Cooperative Highway Research Program (NCHRP) Report 153

in 1974 to NCHRP Report 230 in 1980 and eventually to

NCHRP Report 350 in 1993 [2], which was formally adopted

by Federal Highway Administration (FHWA) and established in

1998 for new hardware installation on the National Highway

System (NHS). An updated version of evaluation procedures

and implementation plans was published by the American

Association of State Highway and Transportation Officials

(AASHTO) in the year 2009, called MASH [1]. Primary focus

of modifications in this manual included:

Updated test vehicles and impact condition

Elimination of ambiguities and inconsistencies

Consolidation of test matrices and

Rigorous reporting procedures.

Over the past couple of decades, FHWA has acknowledged

and motivated the use of Finite Element (FE) based crash

simulations for safety assessment and innovative design

Proceedings of the ASME 2014 International Mechanical Engineering Congress and Exposition IMECE2014

November 14-20, 2014, Montreal, Quebec, Canada

IMECE2014-38167


developments. This provides a means for developers of safety

features to assess impact performance without actual crash

testing. The National Crash Analysis Center (NCAC) at George

Washington University in Washington DC has been a pioneer

institute in development and validation of such FE models

(vehicles, roadside hardware and infrastructure) that are widely

used for computer simulations and crash data analysis by

researchers across the globe. The FHWA and National Highway

Traffic Safety Administration (NHTSA), through NCAC, have

put together a comprehensive archive of FE models that have

great potential to significantly improve the criteria’s and tools

used to design highways and various roadside elements

associated with them. References [3], [4], [5] and [6] are among

several other relevant research reports that successfully use

FEM in conjugation with LS-DYNA to simulate roadside crash

scenarios and hence assess roadside safety implications.

With recent developments in CAFE standards dictating the

need for environment friendly and fuel efficient cars,

automobile manufactures have focused their technologies on

lightweighting their vehicle designs. LW designs are definitely

among the most eligible candidates for future vehicles;

accordingly the significance of their interaction, under impact

conditions, with existing roadside hardware needs to be

evaluated for safety performance. References [7] and [8],

explored and analyzed various modeling techniques used to

evaluate impact response of composite materials in automotive

structures and investigated the opportunities in vehicle weight

reduction in order to evaluate their impact on crashworthiness.

Complimentary to this research, we present a comprehensive

evaluation of safety performance of LW vehicle models under

interaction with existing roadside hardware, in accordance with

the MASH criteria.

MODEL DESCRIPTIONS Primary objectives under this research included the

development of detailed FE models for test vehicles, baseline as

well as lightweight models (BL and LW), and the most common

roadside safety hardware – longitudinal barriers (test articles) in

order to perform computer based crash simulations and

subsequently evaluate their impact performance, hence

providing a detailed analysis of roadside safety assessment for

future vehicle designs under MASH guidelines.

Vehicle Models Three vehicle models with AASHTO designation 1100C,

1500A and 2270P, Table 1, were selected as representative test

vehicles under this research. From the available archive of FE

models at NCAC – 2010 Toyota Yaris (small car), 2001 Ford

Taurus (midsize sedan) and 2007 Chevy Silverado (pickup

truck), were identified as belonging to the selected classification

of AASHTO designations and accordingly utilized in this study.

A comprehensive description on development and validation of

these FE models can be found under references – [9], [10], [11],

[12], [13] and [14].

Table 1. Vehicle designation and gross static mass

Test Vehicle Designation and Type

Target vehicle weight, lb (kg)

Acceptable variation, lb (kg)

1100C (Passenger Car) 2420 (1100) ± 55 (25)

1500A (Passenger Car) 3300 (1500) ± 220 (110)

2270P (Pickup Truck) 5000 (2270) ± 110 (50)

Table 2. Selected test vehicle and their corresponding LW variants

(a) 2010 Toyota Yaris AASHTO Designation – 1100C

BL LW15 LW25

1100 kg (2420 lbs.)

935 kg (2061 lbs.)

825 kg (1819 lbs.)

(b) 2001 Ford Taurus AASHTO Designation – 1500A

BL LW15 LW25

1500 kg (3307 lbs.)

1275 kg (2811 lbs.)

1125 kg (2480 lbs.)

(c) 2007 Chevy Silverado AASHTO Designation – 2270P

BL LW15 LW25

2270 kg (5000 lbs.)

1930 kg (4255 lbs.)

1703 kg (3755 lbs.)

Selected FE models (BL version) were developed using

reverse engineering and were thoroughly verified using New

Car Assessment Program (NCAP) frontal impact tests. These

models were also successfully validated against side impact

tests; IIHS (Insurance Institute for Highway Safety) offset

deformable barrier tests and centerline pole tests, assuring their

robustness across various impact scenarios. Since the primary

focus of this research is to evaluate barrier performance under

interaction with LW design vehicles, selected BL models were

appropriately scaled in density to generate two LW variants

with 15% (LW15) and 25% (LW25) reduction in weight, Table

2. Relevant FE model info and density scaling parameters for

the LW variants are listed in Table 3.

Table 3. Test vehicle FE model info and LW parameters

Toyota Yaris

1100C Ford Taurus

1500A Chevy Silverado

2270P

Nodes 393,255 921,945 262,061

Elements 378,422 973,370 251,425

Parts 921 803 603

LW parts 729 609 491

Density Scaling LW15 0.75 % 0.79 % 0.75 %

LW25 0.567 % 0.65 % 0.567 %


Rigorous LW modeling techniques such as plastic and

composite intensive material modeling were not exercised under

this research since the goal was to assess barrier performance

and not vehicle crashworthiness. Also, new material modeling

would implicitly require extended validation and verification of

modified FE models. Accordingly, BL models were only scaled

in density whilst maintaining structural stiffness and Center of

Gravity (CG) location. This enabled generating theoretical LW

variants for existing BL models; which in turn would represent

future vehicle designs. Another reason for maintaining BL

material models, structural stiffness and CG locations, was to

have minimum distinct variables within analyzed cases so that

LW models can be relatively compared against BL models, with

gross static mass being the only distinct variable.

Barrier Models Among most commonly used longitudinal barriers on US

highways, the following three kinds were selected from the

available archive at NCAC, Table 4.

Table 4. Test articles – Longitudinal Barriers

(a) New Jersey Barrier – NJB

(b) Strong-Post W-Beam Guardrail – G4(1S)

(c) PennDOT W-Beam Transition – Wtrans

Table 5. Test article FE model info

NJB G4(1S) Wtrans Nodes 12,836 133,910 118,227

Elements 12,435 137,781 121,676

Parts 2 23 43

These barriers were representative of three major

categories (classified according to stiffness) under the MASH

roadside safety features. NJB represented rigid barriers

spanning 32” above pavement, G4(1S) represented flexible/

semi-rigid barriers with a top rail height of 27.75” and Wtrans

represented transition barriers (combination of previous two)

with rail height of 31” adjacent to a 42” bridge rail. These

models were developed based upon explicit geometry of all

constituent components such as posts, blockouts, nested rails,

anchor plates, and suitable connectors. Characteristic material

models and sectional properties were assigned in order to

ensure correct mass, inertia and stiffness for the model. Soil was

modeled using solid elements, and incorporating the shape/size

of the posts, in order to simulate post-soil interactions. For a

comprehensive description on FE development and verification

of these models kindly refer to [15], [16] and [17].

TEST MATRICES AND IMPACT CONDITIONS The principle objective of MASH crash testing guidelines

is to provide an established minimum level of performance for

roadside safety hardware whilst providing a basis for comparing

different designs within a class. In order to accomplish this,

MASH procedures take into consideration worst, or the most

critical conditions when defining test parameters such as test

vehicle mass, impact speed, angle of approach, point of impact

etc. Combined together, these parameters are expected to

represent extreme impact conditions one would expect in real-

world crashes [1]. In the following descriptions, we will discuss

these parameters while appropriately choosing those that

compatible with our set of test vehicles and test articles. This

will help us generate required test matrices in order to simulate

MASH recommended test procedures.

Test Levels According to MASH, a Test Level (TL) is defined by the

combination of impact conditions, such as speed and angle of

approach, and the type of test vehicle under consideration.

Reconstruction analysis of run off-the-road passenger vehicle

crashes on high-speed roadways, [18], indicated that impact

speeds of 62 mph (100 km/hr) and angles of ~25° approximated

the 85th

percentile of the respective real world conditions.

Accordingly these values were selected to represent the limiting

conditions. For low-speed, low-volume roadways, impact

speeds were reduced to 44 and 31 mph. Therefore, for the

selected set of test vehicles under this research, MASH

recommended Test Levels were selected as TL1, TL2 and TL3;

as listed in Table 6.

Table 6. Selected Test Levels

Test Level

Test Vehicle Designation and Type

Test Conditions Speed

mph (km/h) Angle in degrees

TL 1 1100C (Passenger Car) 1500A (Passenger Car) 2270P (Pickup Truck)

31 (50.0) 25

TL 2 44 (70.0) 25

TL 3 62 (100.0) 25

Further classification of Test No. was identified and

obtained from MASH based upon the selected combinations of

test vehicles and test articles. A brief description of these tests,

as obtained from MASH, is as follows.


Table 7. Test Matrices

Test Level

Test Article Test No. *

Test Vehicle

Test Vehicle Variants

Impact Speed mph (km/h)

Impact Angle θ, degrees

Impact Point, c

Evaluation Criteria, b

TL 1 NJB / G4(1S) /

Wtrans

1-10 1-11 1-20

d

1-21

1100C 1500A 2270P

BL LW15 LW25

31 (50.0) 25 CIP A,D,F,H,I

TL 2 NJB / G4(1S) /

Wtrans

2-10 2-11 2-20

d

2-21

1100C 1500A 2270P

BL LW15 LW25

44 (70.0) 25 CIP A,D,F,H,I

TL 3 NJB / G4(1S) /

Wtrans

3-10 3-11 3-20

d

3-21

1100C 1500A 2270P

BL LW15 LW25

62 (100.0) 25 CIP A,D,F,H,I

b – See Table 8, c - See Figure 1, d - Test is Optional

* Test No. -10, -20 refer to passenger cars whereas -11 and -21 refer to pickup trucks

Test 10 is designed to investigate a barrier’s ability to

successfully contain and redirect small passenger vehicles

impacting within the length-of-need. For small cars, the primary

concerns are the potential for vehicle under-ride, wheel snag,

rollover, and head-slap. In order to evaluate full range of barrier

impact performance, testing should be conducted with the

barrier at the maximum allowable height for small car tests.

This is especially true for post-and-beam barrier systems to

maximize the risk of under-ride and wheel snag.

Tests 11 and 21 provide maximum strength tests for Test

Levels 1 through 3 and verify a barriers performance for

impacts involving light trucks and SUVs. Due to the high

rollover frequencies observed in crash data historical full-scale

crash testing with light truck vehicles, Tests 11 and 12 are

required for all barrier systems. These tests are also required to

meet all occupant risk measures, including both lateral and

longitudinal occupant impact velocity (OIV) and occupant

ridedown acceleration (ORA) values.

Test 20 for a transition section is an optional test to

evaluate the occupant risk and post-impact trajectory for all Test

Levels. It should be conducted if there is reasonable uncertainty

regarding the impact performance of the system for impacts

with small passenger vehicles.

Accordingly, Test Levels from Table 6 were augmented

with recommended Test No. and are reflected in final test

matrices along with corresponding evaluation criteria’s for

longitudinal barriers, Table 7.

Impact Point Impact point for roadside safety hardware (re-directive

devices) is the point at which the test vehicle first contacts the

test article. Under MASH guidelines, impact locations were

selected to represent critical scenarios that would maximize the

failure of test article under consideration. For longitudinal

barriers, Critical Impact Points (CIPs) were selected to

maximize loading at rail splices and hence maximize the

potential for wheel snag and vehicle pocketing, Figure 1.

(a)

(b)

Figure 1. Schematic representation of impact conditions for

longitudinal barriers. Distance X represents the location of CIP (a) Standard guardrail systems (b) Transition guardrail systems [1]

The computer program Barrier VII has been widely used as

the primary tool for identifying CIP locations for longitudinal

barriers [19] and more recently, LS-DYNA has been utilized for

this same purpose. NJB does not require a definite CIP location

since the cross-section remains constant across the longitudinal

length of the barrier, however for G4(1S) and Wtrans guardrail


systems, CIP was identified by ensuring that the selected

location resulted in maximum loading of the rail splice.

CRASH SIMULATIONS A total of 81 numerical simulations encompassing the

entire spectrum of test vehicles (3), vehicle variants (×3), test

articles (×3) and test levels (×3) were designed according to test

matrices defined under Table 7. Simulation time of 0.5 sec was

selected all cases in order to allow sufficient time for the test

vehicle to traverse post-impact so that relevant dynamics

performance factors can be computed. Discussing the entire set

of results from 81 simulations, their analysis, and their

corresponding MASH assessments is beyond the scope of this

paper, accordingly we shall focus on the following pairs of test

vehicles and test articles where entire pool of results cannot be

presented:

1) Yaris v/s G4(1S)

2) Taurus v/s NJB and

3) Silverado v/s Wtrans

In order to identify specific cases, from within the entire

matrix of simulations, we shall use the following case ID

nomenclature – VAM_S.

Where:

V ≡ first initial of test vehicle name

A ≡ first initial of test article name

M ≡ test vehicle model identifier

S ≡ Test level speed.

For example:

Yaris – NJB – Baseline – 50 km/hr ≡ YNBL_50

Taurus – G4(1S) – LW15 – 70 km/hr ≡ TG15_70

Silverado – Wtrans – LW25 – 100 km/hr ≡ SW25_100

First and foremost, every case was assessed for stability by

assessing the distribution of energy associated with the crash

event. Figure 2 provides the global energy summaries for

YGBL_100, TNBL_100 and SWBL_100. These plots indicate

a relatively constant total energy, suggesting that there is no

unusual characterization in the simulation that would result in

unrealistic sink (trough) or spike (peak) of energy. The kinetic

energy associated with the motion of the vehicle gradually

decreases post-impact and consequently internal energy

increases as vehicle components absorb energy via deformation.

Interface energy, which is associated with the friction between

internal components and vehicle-to-barrier interaction, also

gradually increases during the simulation. Hourglass energy

also remains negligible, compared to other energies, throughout

the simulations, ensuring efficient and consistent element

formulation.

(a)

(b)

(c)

Figure 2. Energy Balance (a) YGBL_100 (b) TNBL_100 (c) SWBL_100. Note: X axis represents time in sec and Y axis

represents global energies in Joules


Table 8. MASH recommended Safety Evaluation Guidelines

Evaluation Factors Evaluation Criteria Applicable

Tests *

Structural Adequacy

A. Test article should contain and redirect the vehicle or bring the vehicle to a controlled stop; the vehicle should not penetrate, underride, or override the installation although controlled lateral deflection of the test article is acceptable.

10, 11, 20, 21, …

B. The test article should readily activate in a predictable manner by breaking away, fracturing or yielding.

…

C. Acceptable test article performance may be by redirection, controlled penetration or controlled stopping of the vehicle.

…

Occupant Risk

D. Detached elements, fragments, or other debris from the test article should not penetrate or show potential for penetrating the occupant compartment, or present undue hazard to other traffic, pedestrians, or personnel in a work zone. Deformations of, or intrusions into, the occupant compartment should not exceed limits set forth in Section 5.3 and Appendix E [1]

All

E. Detached elements, fragments, or other debris from the test article, or vehicular damage should not block the driver’s vision or otherwise cause the driver to lose control of the vehicle.

…

F. The vehicle should remain upright during and after collision. The maximum roll, pitch, and yaw angles are not to exceed 75 degrees.

All except those listed in Criteria G

G. It is preferable, although not essential, that the vehicle remain upright during and after collision. …

H. Occupant Impact Velocities (OIV) should satisfy the following limits:

Component Preferred Maximum

Longitudinal and Lateral 30 ft/sec (9.1 m/sec) 40 ft/sec (12.2 m/sec) 10, 11, 20, 21, …

Longitudinal 10 ft/sec (3.0 m/sec) 16 ft/sec (4.9 m/sec) …

I. Occupant Ridedown Acceleration (ORA) should satisfy the following limits:

Component Preferred Maximum

Longitudinal and Lateral 15.0 G 20.49 G 10, 11, 20, 21, …

Post-impact Vehicular Response

J. Through M. reserved

N. Vehicle trajectory behind the test article is acceptable …

* Only tests conducted under this research have been listed under Applicable Tests, the rest are indicated in (…)

EVALUATION CRITERIA We will now focus on the evaluation of MASH

recommended dynamic performance factors: (1) Structural

Adequacy, (2) Occupant Risk and (3) Post-impact Vehicular

Response and their corresponding evaluation criteria’s, Table 8,

for the test matrices selected under this research. Based on

simulation results and corresponding evaluations, we will

discuss the safety implication of future vehicle designs. We will

address each relevant criterion and present a comprehensive and

relative assessment between BL and LW models.

1) Structural Adequacy Structural adequacy represents the preliminary set of safety

evaluation criteria’s that must be satisfied by all test articles

under assessment. Every roadside safety feature, depending on

its intended function, must be able to redirect the vehicle, by

stopping the vehicle in a controlled manner, or by permitting the

vehicle to break through the device [1].

Criteria A: As described in Test Matrices, Table 7,

selected test articles must satisfy Criteria A, Table 8. This

criterion assesses the feature from a structural and a mechanical

point of view. For longitudinal barriers, structural strength is

examined by requiring vehicle containment and redirection – in

a controlled manner. The condition of controlled stopping while

the vehicle remains in contact with the rail is also considered

satisfactory [1]. Geometrical features of a barrier, such as

guardrails, are assessed by examining the engagement zone

between the vehicle and the barrier, hence ensuring that the test

vehicle does not underride or override the installation.

In Annex A, Figure 5, we plot the trace of CG for the test

vehicle as it approaches and departs from the barrier post-

impact. By visual inspection and by noticing the change in slope

of the trace, we can see that the barrier is capable of containing

and redirecting the vehicle. We also notice that the barrier

maintains its structural integrity; that is the vehicle does not

penetrate or rupture the barrier. We also analyze the crash

scenario in different perspectives and at different time instants,

making sure the vehicle does not underride, override or snag

across the barrier. Similar evaluations were made for all


simulations and it was observed that the barriers satisfied

Criteria A under all Test Levels and for all LW variants.

2) Occupant Risk Risk of occupant injury during impact with a highway

safety feature largely depends on the crashworthiness of the

impacting vehicle. It also depends on several other factors such

as the design of occupant compartment, its structural integrity,

equipped restraint systems, seating positions, airbags, occupant

physiology etc. Consequently, relationship between occupant

risk and vehicle dynamics during interaction with a roadside

hardware is extremely difficult to quantify since it involves such

important but widely varying factors. As a de facto standard,

MASH recommends measuring occupant risk based on gross

vehicular accelerations; that is parameters should be measured

with respect to accelerations measured near the vehicle Center

of Gravity [1]. This circumvents any vehicle/occupant

dependent variables, which would normally differ from case to

case. As described in Table 7, selected test articles must satisfy

Criteria D, Criteria F, Criteria H, and Criteria I, Table 8.

Criteria D evaluates occupant risk by taking into account

the deformations and intrusions within the occupant

compartment. MASH recommends limiting values for these

evaluations, that are defined to ensure that deformation and

intrusions do not cause serious injuries. These recommended

values were made whilst considering the limitations of

suggested test procedures and methodologies used to estimate

occupant risk [1]. Since the LW variants were developed solely

by density scaling (as opposed to rigorous material modeling),

occupant compartment deformations and intrusions were

assumed to be “not accurate” representations of the actual

future vehicle designs. Accordingly, Criteria D was not

evaluated under this study.

Criteria F: According to MASH, a key requirement for

occupant risk evaluation is for the impacting vehicle to remain

upright during and after the collision. As an indication of

vehicle stability, the maximum roll or pitch angles, Figure 3, of

the vehicle during and after impact sequence should not exceed

75°, Table 8.

Figure 3. Vehicle Stability Parameters

MASH recommended format for documentation and

reporting of findings under this evaluation includes the

measurements of vehicle angular displacements (roll, pitch and

yaw) in the form of plots, Figure 4, and maximum values,

Annex B Table 9. We can see from Table 9 that test vehicles

remain upright during the course of impact and do not roll,

pitch or yaw over 75°, ensuring successful barrier performance.

Criteria H: MASH also recommends evaluating occupant

risk by measuring the response of a hypothetical, unrestrained

front seat occupant whose motion relative to the occupant

compartment is solely dependent on vehicular accelerations [1].

According to MASH, the “point-mass” occupant is assumed to

move through space until it impacts a hypothetical instrument

panel, windshield, or side structure and consequently is

assumed to experience vehicular accelerations perpendicular to

the contact surface while remaining in contact with the interior

surface. Occupant Impact Velocity (OIV) is one such

performance criteria that takes into account longitudinal and

lateral component of occupant velocity at the instant of impact

[1]. OIV is calculated using the following equation [1]:

*

, ,

0

x y

t

I x yV a dt (1)

Subscripts x and y represent impact velocity in the x or y

direction, a represents vehicular acceleration and t* is the time

when the hypothetical occupant has travelled either 2 ft (0.6 m)

forward or 1 ft (0.3 m) laterally, whichever is smaller [1]. t* is

determined by incremental integration using:

* *

2

,

0 0

,

t t

x yX Y a dt (2)

Where X = 2 ft (0.6 m) and Y = 1 ft (0.3 m). Acceleration is

integrated twice with respect to time to find the value of t* (t

*x

or t*y) at which the RHS equals X or Y. t

* in Eq. (1) is then

taken as the smallest of t*x or t

*y. MASH recommended limits

for OIV under applicable tests are listed in Table 8 and the

results obtained from simulation crash data analysis are listed in

Annex C Table 10. We can see that all crash scenarios, except

for a few, evaluate to preferred OIV values (less than 9.1

m/sec), ensuring successful barrier performance.

Criteria I: Occupant Ridedown Acceleration (ORA) is

another safety performance criteria that takes into account the

highest lateral and longitudinal component of resultant

vehicular accelerations, averaged over the 10 ms (millisecond)

interval of the collision pulse subsequent to the occupant impact

with the associated interior surface [1]. That is, an average of

instantaneous vehicular accelerations subsequent to time t*. In

general however, the averaging duration used to produce


(a) (b) (c)

Figure 4. Vehicle Roll, Pitch and Yaw angles (a) Yaris v/s G4(1S) (b) Taurus v/s NJB (c) Silverado v/s Wtrans.

Note: x-axis represents time in sec and y-axis represents angular displacements in degrees

occupant injury measurements can range from 0.007 to 0.04 sec

depending on the body component [20]. MASH recommended

limits for ORA assessed under applicable tests are listed in

Table 8 and the results obtained from simulation crash data

analysis are listed in Annex C Table 11. We can see that most

crash scenarios evaluate to preferred ORA values (less than 15

G). However two cases, SN15_100 and SN25_100, surpass the

maximum allowable ORA of 20.49G. These are representative

extreme cases since; 1) Silverado is the heaviest test vehicle

under consideration, 2) Both LW15 and LW25 fail the

evaluation at 100 km/hr, the highest Test Level and 3) NJB is

rigid barrier, meaning it undergoes no deformation; accordingly

it does not absorb impact energy and hence results in higher

ORAs.

3) Post-impact Vehicular Response Post-impact vehicular trajectory is a measure of the

potential of the vehicle to result in a secondary collision with

other vehicles and/or fixed objects, thereby increasing the risk

of injury to the occupants of the impacting vehicle and/or other

vehicles [1]. Recommended matrices for selected set of test

vehicles and test articles do not require the evaluation of this

dynamics performance factor and accordingly the barriers were

not assessed under this criterion.

CONCLUSIONS In this paper, we utilize FEM for modeling and simulating

different crash scenarios in order to evaluate the safety

implications of future lightweight (LW) vehicle designs. Three

representative vehicle models, conforming to MASH weight

classification, were selected from the FE library available at

NCAC. These baseline (BL) models were appropriately LW

modeled whilst maintaining structural stiffness and CG

locations. Two variants per test vehicle, one with 15% and

another with 25% reduction in weight were modeled to simulate

hypothetical versions of future LW vehicles. Entire set of test

vehicles was then analyzed under crash conditions with 3

different longitudinal barriers in order to evaluate their safety


performance. Based on MASH guidelines, appropriate test

matrices and impact conditions were selected and the test

articles were evaluated under 3 Test Levels. Subsequently, each

crash scenario was successfully assessed for structural adequacy

and occupant risk following MASH evaluation criteria.

Preliminary stability analysis was performed on each case

by gauging global energy distribution during the course of

simulation and ensuring that the physical law of energy balance

is satisfied. Under MASH guidelines for safety assessment,

each scenario was then evaluated for Criteria A, F, H and I.

When compared against reference BL models, LW variants

show very good conformance in overall impact dynamics and

vehicle stability. Selected barriers successfully performed under

Criteria A (vehicle containment and redirection) with no wheel

snag, underride or override. They also successfully performed

under Criteria F (vehicle stability), with roll, pitch and yaw

angles within MASH critical limits. Barriers also performed

well under Criteria H and I (OIV and ORA), ensuring occupant

safety. Results under this study show that existing roadside

infrastructure designs are efficient in protecting occupants of up

to 25% LW vehicles at up to 100 km/hr impact velocities.

However, a rigorous approach with future LW design material

models is recommended for detailed analysis, including the

evaluation of occupant compartment intrusions.

ACKNOWLEDGMENTS We would like to thank Eduardo Arispe from DOT for his

continual support. This research task is sponsored under DOT

IDIQ No. DTFH61-09-D-00001.

REFERENCES [1] “Manual for Assessing Safety Hardware (MASH)”, 2009,

published by the American Associations of State Highway

& Transportation Officials (AASHTO), Washington, DC.

[2] Ross, H. E., Sicking, D. L., Zimmer, R. A., Michie, J. D.,

1993, “Recommended Procedures for the Safety

Performance Evaluation of Highway Features,” National

Cooperative Highway Research Program (NCHRP) Report

350. Transportation Research Board, National Research

Council, Washington, DC.

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ANNEX A: STRUCTURAL ADEQUACY

0 .0 sec 0 .2 sec 0 .35 sec 0 .5 sec

(a) Yaris – G4(1S) – BL – 50 km/hr

0 .0 sec 0 .2 sec 0 .35 sec 0 .5 sec

(b) Taurus – NJB – LW15 – 70 km/hr

0 .0 sec 0 .2 sec 0 .35 sec 0 .5 sec

(c) Silverado – Wtrans – LW25 – 100 km/hr

Figure 5. Vehicle containment and redirection (a) YGBL_50 (b) TN15_70 (c) SW25_100


ANNEX B: OCCUPANT RISK– VEHICLE STABILITY (ROLL, PITCH AND YAW)

Preferred Critical

Angular Displacement < 75° > 75°

Table 9. Maximum values for vehicle roll, pitch and yaw in degrees

Criteria F 2010 Toyota Yaris

2001 Ford Taurus

2010 Chevy Silverado NJB G4(1S) Wtrans NJB G4(1S) Wtrans NJB G4(1S) Wtrans

BL

TL1 Roll 6.48 3.87 2.40 9.79 1.98 2.73 5.24 0.97 3.75

Pitch 8.21 1.67 1.92 2.96 1.57 2.37 7.42 2.19 1.69

Yaw 37.36 31.99 35.08 31.13 29.24 28.70 37.53 22.79 32.59

TL2 Roll 3.62 7.44 3.91 17.11 2.15 3.18 13.34 11.76 12.16

Pitch 12.97 1.52 3.79 4.88 2.72 3.08 14.37 12.87 7.33

Yaw 39.95 32.25 37.89 38.16 39.06 33.29 29.38 30.41 36.79

TL3 Roll 6.79 8.18 11.84 20.09 6.10 6.56 8.19 17.36 33.18

Pitch 8.96 4.00 11.75 5.10 8.35 6.49 8.08 17.33 26.57

Yaw 36.21 37.08 43.32 41.81 29.83 48.12 30.37 32.47 43.25

LW15

TL1 Roll 7.41 2.75 2.31 9.56 2.25 2.73 5.81 1.05 2.90

Pitch 8.69 1.17 1.24 2.99 1.31 2.25 7.54 1.92 1.50

Yaw 38.34 36.05 35.17 31.30 33.59 28.55 36.96 20.65 31.94

TL2 Roll 3.87 7.21 4.04 12.98 3.23 2.52 21.72 2.27 10.77

Pitch 13.87 1.31 3.16 3.96 3.59 3.39 19.05 5.07 7.01

Yaw 40.45 35.54 36.78 38.27 33.88 35.27 31.05 36.73 35.91

TL3 Roll 5.12 16.66 5.09 18.72 6.12 7.47 9.88 13.14 37.02

Pitch 11.99 4.64 6.36 4.62 7.54 4.42 9.44 17.03 26.51

Yaw 38.25 36.14 42.30 43.98 35.77 49.71 29.94 34.99 37.74

LW25

TL1 Roll 4.48 2.11 2.25 9.79 1.85 2.35 5.94 2.28 2.41

Pitch 11.26 1.01 1.11 3.36 1.22 1.90 7.72 1.81 2.08

Yaw 39.33 37.21 35.27 36.89 32.32 27.78 36.22 23.42 31.11

TL2 Roll 4.31 6.60 2.74 10.99 1.62 3.17 21.15 16.03 10.55

Pitch 17.62 1.99 3.31 3.61 1.16 3.49 17.38 16.84 6.36

Yaw 39.67 37.69 36.73 36.98 39.44 34.74 34.04 28.01 35.59

TL3 Roll 4.25 8.15 4.74 16.61 2.64 7.51 11.04 11.47 37.37

Pitch 13.95 5.92 7.33 4.42 2.90 4.18 11.69 17.45 26.07

Yaw 37.08 48.03 38.03 45.00 46.14 48.65 29.33 36.29 37.36


ANNEX C: OCCUPANT RISK – OIV AND ORA

Preferred Safe Critical

OIV OIV < 9.1 9.1 < OIV < 12.2 12.2 < OIV

ORA ORA < 15 15 < ORA < 20.49 20.49 < ORA

Table 10. Occupant Impact Velocity (OIV) in m/sec

Criteria H – OIV 2010 Toyota Yaris

2001 Ford Taurus


BL

TL1 Longitudinal 3.37 4.31 3.83 2.81 3.85 3.21 2.63 4.13 3.24

Lateral 4.63 4.63 4.52 4.51 3.95 4.78 4.42 3.22 4.08

TL2 Longitudinal 4.71 5.88 6.43 4.37 5.34 4.89 3.01 5.27 4.92

Lateral 6.30 5.23 6.40 5.80 4.83 6.97 5.23 4.13 5.68

TL3 Longitudinal 5.96 8.17 8.93 6.18 7.86 7.21 4.98 6.70 7.14

Lateral 8.41 5.58 8.86 7.98 4.90 9.73 7.92 4.68 7.70

LW15

TL1 Longitudinal 3.37 3.93 3.74 2.65 3.65 3.31 2.67 4.39 3.00

Lateral 4.56 4.73 4.51 4.15 4.10 4.50 4.26 3.35 4.03

TL2 Longitudinal 4.62 5.43 5.92 4.32 5.02 4.79 3.04 5.52 4.53

Lateral 6.26 5.68 6.53 5.77 4.67 6.85 5.39 4.07 5.66

TL3 Longitudinal 6.03 8.14 8.40 6.21 7.92 7.12 4.64 6.51 6.54

Lateral 8.68 5.81 9.27 8.19 5.20 9.68 7.76 5.25 7.95

LW25

TL1 Longitudinal 3.18 4.00 3.61 2.89 3.33 3.09 2.50 4.33 3.08

Lateral 4.36 4.81 4.43 4.44 4.42 4.19 4.09 3.66 3.95

TL2 Longitudinal 4.52 5.51 6.10 4.08 5.12 4.68 3.18 5.45 4.93

Lateral 6.28 5.61 6.42 6.08 4.95 6.75 5.79 4.09 5.50

TL3 Longitudinal 6.03 7.60 8.30 6.04 7.76 6.91 4.85 6.78 6.72

Lateral 8.67 6.05 9.35 8.29 5.90 10.01 7.31 5.21 7.82

Table 11. Occupant Ridedown Acceleration (ORA) in G’s

Criteria I – ORA 2010 Toyota Yaris

2001 Ford Taurus


BL

TL1 Longitudinal 1.25 4.23 1.20 2.33 8.14 1.76 4.50 7.87 4.69

Lateral 2.80 3.13 3.25 4.51 9.45 5.25 5.21 5.37 6.86

TL2 Longitudinal 1.94 10.1 3.32 3.07 6.92 3.13 8.47 7.77 5.59

Lateral 2.97 5.94 3.75 5.83 7.88 7.68 10.42 6.08 8.19

TL3 Longitudinal 2.57 12.2 14.42 4.33 15.15 11.29 13.60 11.31 12.69

Lateral 7.16 8.2 13.62 6.71 16.98 11.2 18.86 10.94 8.34

LW15

TL1 Longitudinal 2.51 3.12 1.77 2.95 6.62 3.84 3.68 7.34 5.01

Lateral 3.01 3.36 5.19 4.78 6.82 8.72 8.18 4.19 6.00

TL2 Longitudinal 1.82 12.59 2.31 3.58 8.94 4.13 5.60 9.27 4.98

Lateral 3.65 4.61 8.28 5.89 8.30 10.47 15.32 8.45 8.34

TL3 Longitudinal 2.87 13.45 10.42 3.69 19.68 8.49 15.40 12.06 12.01

Lateral 8.24 9.59 11.06 7.97 19.62 9.39 22.13 8.26 11.14

LW25

TL1 Longitudinal 1.59 2.58 1.60 2.66 2.43 2.15 3.03 6.82 3.75

Lateral 4.91 2.46 5.94 3.71 4.40 7.42 7.06 4.62 5.36

TL2 Longitudinal 2.39 10.81 2.80 4.45 10.18 2.96 5.72 7.26 5.46

Lateral 4.54 6.31 8.98 6.9 8.38 10.05 17.27 5.35 9.67

TL3 Longitudinal 2.88 12.31 9.54 5.02 11.20 7.84 12.16 11.88 9.45

Lateral 9.31 11.51 12.18 7.73 14.64 9.5 20.75 10.59 11.18

analyzing roadside safety implications of future vehicle

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