____________________________________________________________________________ 

This document is available to the public from the National Technical Information Service, Springfield, VA 22161 

DOT HS 809 894 November 2005 

Technical Report 

Rollover Crash Mechanisms and 

Injury Outcomes for Restrained Occupants 

Published By: 

NHTSA’s 

National Center for Statistics and Analysis 
____________________________________________________________________________ 

This document is available to the public from the National Technical Information Service, Springfield, VA 22161 

This publication is distributed by the U.S. Department of Transportation, National Highway Traffic 

Safety Administration, in the interest of information exchange. The opinions, findings, and 

conclusions expressed in this publication are those of the author and not necessarily those of the 

Department of Transportation or the National Highway Traffic Safety Administration. The United 

States Government assumes no liability for its contents or use thereof. If trade or manufacturers’ 

names are mentioned, it is only because they are considered essential to the object of the publication 

and should not be construed as an endorsement. The United States Government does not endorse 

products or manufacturers. 
____________________________________________________________________________ National Center for Statistics and Analysis, 400 Seventh St., S.W., Washington, DC 20590 

iii

 Technical Report Documentation Page 

1. Report No.

HS 809 894 

2. Government Accession No. 3. Recipients's Catalog No. 

5. Report Date 

November 2005 

4. Title and Subtitle

Rollover Crash Mechanisms and Injury Outcomes 

for Restrained Occupants 6. Performing Organization Code 

NPO-121 

7. Author(s)

Ana María Eigen, D.Sc. 

8. Performing Organization Report No.

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS)n code

Mathematical Analysis Division, Office of Traffic Records and Analysis 

National Center for Statistics and Analysis 

National Highway Traffic Safety Administration 

U.S. Department of Transportation 

NPO-121, 400 Seventh Street, S.W. 

Washington, DC 20590 

11. Contract of Grant No. 

13. Type of Report and Period Covered

NHTSA Technical Report 

12. Sponsoring Agency Name and Address

Mathematical Analysis Division, Office of Traffic Records and Analysis 

National Center for Statistics and Analysis 

National Highway Traffic Safety Administration 

U.S. Department of Transportation 

NPO-121, 400 Seventh Street, S.W. 

Washington, DC 20590

14. Sponsoring Agency Code

15.Supplementary Notes 

Special thanks to Dr. David Smith, Office of Vehicle Safety, Mr. Dennis Utter, and Dr. Chou-Lin Chen, both of NCSA, for making the completion of this report possible.

16. Abstract 

The present study amplified findings presented in “Examination of Rollover Crash Mechanisms” (2003), “Crash Attributes That Influence the Severity of Rollover 

Crashes” (2003), and “Characterization of Attributes Applicable to a Rollover Crash Severity Metric” (2004) relevant to restrained occupants. Identification of the 

three crash occupant populations was reviewed: unejected belted, unejected unbelted, and ejected unbelted. Belted occupants involved in multiple-vehicle rollover 

crashes were studied owing to their elevated serious injury rates. Harm analysis and case reviews were presented for the belted occupants involved in singlevehicle rollover crashes. Two alternate crash populations were studied owing to their injury implications and pure rollover characteristics. 

Multiple-vehicle rollover crash belted occupants were selected owing to the elevated injury risk associated with this crash configuration. Among belted rollover 

crash occupants, the injury rate for multiple-vehicle rollover crash occupants was twice as high as for single-vehicle rollover crash occupants. Among unbelted 

rollover crash occupants, the difference between the injury rates for the crash configurations was negligible. 

Single-vehicle rollover crashes with nonfixed object impacts were selected because these simulated a pure rollover situation. These impacts also excluded abruptly 

stopped rollover crashes, especially those for which the roof was stopped by a fixed object. From these crashes, representative cases were selected for analyses of 

HARM, crash mechanisms, and injury patterns. 

HARM is a measure of societal cost of injuries sustained by motor vehicle crash occupants. From the HARM analysis, two injured body regions were identified for 

further study. These were: the head and thorax. Elevated HARM values were noted in rollovers with one roof to ground contact for head injuries and the second 

roof to ground impact for thoracic injuries. 

The final section presented hard-copy case review based upon the identified injuries associated with roof to ground impacts. Head injuries in rollovers with one 

roof to ground contact were consistent with the work of Burel (2003), who found the highest dummy head accelerations during the first revolution. These results 

were based upon modeling. Thoracic injuries were divided into near-side and far-side injuries. The near-side occupant thoracic injury source was generally 

associated with the side hardware and the far-side occupant thoracic injury source was generally associated with the safety belt. Further, tripping acceleration was 

evident in most of these cases. The present work seeks to outline the tripping acceleration and complex motion phenomena predicated on the injury mechanisms 

identified in Eigen (2004).

17. Key Words 

rollover crashes, quarter turns, MAIS 3+F injuries, 

tripping acceleration, head injuries, thoracic injuries 

18. Distribution Statement

Document is available to the public through the National 

Technical Information Service, Springfield, VA 22161

19. Security Classif. (of this report)

 Unclassified 

20. Security Classif. (of this page)

 Unclassified 

21. No of Pages

44 

22. Price

Form DOT F1700.7 (8-72) Reproduction of completed page authorized 
____________________________________________________________________________ National Center for Statistics and Analysis, 400 Seventh St., S.W., Washington, DC 20590 

iv
____________________________________________________________________________ National Center for Statistics and Analysis, 400 Seventh St., S.W., Washington, DC 20590 

v

Table of Contents 

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

2. Introduction................................................................................................................................. 2

3. Background ................................................................................................................................. 2

4. Methodology................................................................................................................................ 3

5. Definitions and Population Identification ................................................................................. 3

5.1 Evaluation of Crash Severity............................................................................................................... 3

5.2 Definitions........................................................................................................................................... 4

5.3 Identification of Populations of Interest and Constraints .................................................................... 5

6. Rollover Crash Configuration and Its Influences on Occupant Outcome.............................. 5

6.1 Crash Configuration and Injury Severity ............................................................................................ 5

6.2 Crash Configuration and Crash Severity............................................................................................. 6

7. Justification for Inclusion of Belted Unejected Occupants..................................................... 7

7.1 Belted Unejected Occupants Involved in Single-Vehicle Rollover Crashes....................................... 7

7.2 Belted Unejected Occupants Involved in Multiple-Vehicle Rollover Crashes ................................. 10

8. Discussion of Belted Unejected Population........................................................................... 10

8.1 General Case ..................................................................................................................................... 10

8.2 Specific Case: Multiple-Vehicle Rollover Crash Configuration for Belted Occupants .................... 11

8.3 Analytical Considerations ................................................................................................................. 13

9. Societal Cost of Injuries to Belted Unejected Occupants Involved in Single-Vehicle, 

Nonfixed Object Rollover Crashes .......................................................................................... 14

9.1 Description of Chosen Societal Cost Method – HARM.................................................................... 14

9.2 Results Leading to Case Reviews...................................................................................................... 14

10. Identification of Case Review Focus....................................................................................... 16

10.1 Four Illustrative Tripping Damage Cases – High Side Force............................................................ 16

10.2 Pre-Rollover Complex Motion.......................................................................................................... 27

10.3 Discussion of Case Review Results .................................................................................................. 30

10.4 Qualitative Results of Individual Case Analysis ............................................................................... 30

11. Computer Modeling .................................................................................................................. 30

11.1 Discussion of Modeling Results........................................................................................................ 30

11.2 Observation Based upon Modeling – Tripping Acceleration............................................................ 32

12. Conclusions ............................................................................................................................................. 33

12.1 General Conclusions based upon Previous Work.............................................................................. 33

12.2 Rollover Population Selection........................................................................................................... 33

12.3 Crash Configuration and Its Influence on Occupant Outcome.......................................................... 33

13. Recommendations.................................................................................................................... 35

13.1 Future Work Recommendations........................................................................................................ 35

13.2 Recommendations for NASS Researchers ........................................................................................ 35

13.3 Recommendation for Rollover Data Analysts................................................................................... 35

14. References................................................................................................................................. 36
NHTSA’s National Center for Statistics and Analysis 400 Seventh St., S.W., Washington, D.C. 20590 1 
NHTSA’s National Center for Statistics and Analysis 400 Seventh St., SW., Washington, DC 20590

1 Executive Summary 

In continued response to the rollover situation in the United States and parameters identified in 

subsequent research, more information is available regarding: 

• rollover population selection; 

• crash configuration and its influences on occupant outcome; 

• application of societal costs to injuries sustained by restrained unejected occupants 

(occupants retained completely within the occupant compartment exclusive of partial or 

full ejections) in rollover crashes; and 

• association of prevalent crash modes and injury characteristics for restrained unejected 

occupants. 

This document will: 

• justify the selection of belted unejected occupants; 

• discuss societal implications of injuries sustained by this group; and 

• identify injury mechanisms and associated crash parameters.

Current findings indicate that: 

• head and thorax injuries were the highest contributors to societal cost; 

• planar impacts prior to rollover need to include a planar crash severity (delta V) in 

addition to the rollover severity (Number of roof to ground contacts); 

• the magnitude of the trip pulse influences the number of roof to ground impacts and may 

increase Abbreviated Injury Scale (AIS) 3+ chest injury risk; and 

• most Maximum AIS (MAIS) 3+ head injuries occur in rollovers with one roof to ground 

contact. 
2

2 Introduction 

The study of rollover crash severity is dependent upon its ability to be quantified for benefits 

analysis. Upon determining a societal good coming from a sophisticated benefit cost analysis 

model, such as HARM, a severity metric may be found to be dependent upon some 

countermeasure. In general, the early rollover countermeasures continue to be in force. These 

include: 

• ejection prevention; 

• intrusion control (roof strength); and 

• safety belt improvements. 

Pursuant to the review of relevant occupant selection and justification of inclusion, two 

subgroups were identified for review in this document. Among the restrained occupants, the 

most numerous group of relevant occupants, the multiple-vehicle configuration and singlevehicle nonfixed-object crashes constituted two opportunities for improvement. Multiple-vehicle 

belted rollover crash occupants had an injury rate twice as high as for single-vehicle belted 

rollover crash occupants. Among restrained occupants, the single-vehicle rollover crashes 

without fixed-object involvements were selected as a surrogate for the pure rollover case. 

3 Background 

Since the early 1980s, the pursuit of a rollover severity metric has intrigued researchers. 

McGuigan (1980) and Najjer (1980) considered energy absorption surrogates similar to delta V. 

The concept of a several-tiered severity metric also emerged when considering the planar and 

rollover components of the crash. Until 1995, insufficient refinement in the collection of the 

number of quarter turns disallowed the consideration of roof to ground impacts. Currently, a 

study of this nature was permissible owing to the detailed data available and the number of years 

since the inception of this level of detail. 

“Examination of Rollover Crash Mechanisms and Occupant Outcomes” (DOT HS 809 692, 

2003) examined the first phase of recent rollover severity metric review. It consisted of initial 

identification of a rollover data set and associated vehicle and occupant parameters. At the 

conclusion of DOT HS 809 692, issues were identified pursuant to the initial study and future 

avenues of study were proposed. The areas of study were determined via analysis of National 

Automotive Sampling System (NASS) Crashworthiness Data System (CDS) data, 1995 through 

2001. This work presents the subsequent findings using the NASS CDS data, 1995 through 

2002. 

DOT HS 809 692 and Digges (2003) both resulted from the data analysis. Both publications 

presented results prior to significance testing. The significance testing was used to determine 

whether issues identified in CDS merited further study. The findings of the significance testing 

shaped the remainder of the project. These results were reported in Eigen (2004). 
3

Upon identifying the populations and establishing a rollover severity metric, a review of cases 

ensued. The engineering analysis made use of the coded elements, as well as the photographic 

documentation available from the NHTSA Electronic CDS Case Access. 

The final phase, computer modeling, was dependent upon the significant issues and the 

characteristics associated with these crashes. This information was coupled with test data to 

further redefine rollover models for restrained passenger car occupants. 

4 Methodology 

The overall analysis was divided into three components. These were: 

• data analysis and test for significance of results; 

• review of cases and engineering analysis of crash patterns; and 

• computer modeling of crashes based upon supplemental test data. 

This phase of the study focused on the restrained occupants who presented the largest 

opportunity for improvement owing to the magnitude of this population. This population is 

identified and discussed in subsequent sections. Among restrained occupants, this study 

identified rollover crash and injury parameters for: 

• those crashes closest to the state of pure rollover 

• occupants associated with the highest injury risk. 

5 Definitions and Population Identification 

This section provides the crash severity measures used to analyze the data. Further crash, 

occupant, and injury definitions are provided. Based upon the quantification of occupants, and 

crash and injury definitions, the populations of interest are outlined. 

5.1 Evaluation of Crash Severity 

In assessing the true magnitude of a problem not only its population size must be examined. 

Also, some quantifiable attributes must be identified to characterize the problem. These are: 

• exposed population; 

• injury frequency; and 

• injury rates. 
4

5.2 Definitions 

From the rollover crash population, those occupants sustaining MAIS 3 through 6 and fatally 

injured occupants sustaining MAIS 1 and 2 injuries were selected (NHTSA, 2000). These 

injuries will be identified as MAIS 3+F in this document. Occupants subjected to rollovers of 

quantifiable quarter turns were selected and disaggregated based upon crash configuration. 

By virtue of the exposure and the MAIS 3+F injured occupants, a rate of injury could be 

established. The term risk was used in a similar context, as rate of injury, but was not meant to 

identify the statistical constructs of relative or absolute risk. The injury risk represented the 

number of MAIS 3+F injuries sustained for a given rollover subpopulation per 100 occupants 

exposed to rollovers. 

Based upon early rollover studies, roof to ground impacts were proposed as a potential severity 

metric. From 1988 through 1994, NASS CDS allowed for quantification through the third 

quarter turn and aggregated quarter turns as of the first roof to ground impact. This precluded 

any roof to ground impact analysis to be done. In 1995, NASS CDS modified rollover 

quantification and allowed for 16 quarter turns, four complete revolutions and four roof to 

ground impacts, to be recorded. A value aggregating any quantifiable rollover beyond 16 quarter 

turns was also assigned. It was determined that aggregation of 2 or more roof to ground impacts 

provided an adequate severity measure and accurately increased the size of the cell (Eigen, 

2004). Table 1 provides the translation of roof to ground contacts based upon the number of 

quarter turns. 

Table 1: Relationship between Number of Roof 

 to Ground Impacts and Quarter Turns 

Number of Roof to Ground 

Contacts/Impacts 

Number of 

Quarter Turns 

Zero 1 

One 2, 3, 4, 5 

Two-Plus 6, 7, 8, 9, 10, 11, 12, 13, 14, 

15, 16, 16+ 

 Source: NASS CDS, 1995 - 2002 

The number of roof to ground impacts is defined as the number of times the roof brushes, 

touches, or is suspended over the ground in a rollover. This distinction is made, especially in the 

case of severe rollover, when the second quarter turn may constitute no contact with the ground 

or a light brushing. 

Tow-away crashes are disaggregated based upon the number of vehicles involved in the crash. 

Single-vehicle crashes are those in which one vehicle was reported in the crash. Multiplevehicle crashes consisted of any crash in which more than one vehicle was involved. 
5

5.3 Identification of Populations of Interest and Constraints 

Three populations of interest were published in Digges (2003) that were relevant to rollover 

crashes and were used in this study. These populations were: 

• restrained, unejected occupants; 

• unrestrained, unejected occupants; and 

• unrestrained, completely ejected occupants. 

 

These population groups were identified using NASS CDS data from 1995 through 2001. 

Adding the 2002 data does not affect the proportion of these populations. The rollover data set 

represents approximately 1.5 million vehicles transporting nearly 2 million left- and right-frontseat occupants, 12 and older. Approximately 126,000 of these occupants sustained MAIS 3+F 

injuries. The unweighted data consists of 3,871 vehicles and 5,227 occupants with 1,309 

sustained MAIS 3+F injuries. 

The data were restricted to the two front outboard seating positions to insure comparability 

among a variety of vehicle platforms. In this way, the results were not skewed toward vehicles, 

which could transport several occupants. Upon removing other seating positions, occupancy 

rates were comparable, as seen in Digges (2003). 

It should also be noted that vans constituted a very small segment of the population and distorted 

the findings. The vans were retained in the general summarizations but were excluded from 

analysis. 

6 Rollover Crash Configuration and Its Influences on 

Occupant Outcome 

This section explains the disaggregation of the number of vehicles involved in a crash. The 

relationship between the number of vehicles involved and injury severity, and the relationship 

between the number of vehicles and crash severity are discussed. 

6.1 Crash Configuration and Injury Severity 

The initial summarization of data provided conclusions on aggregate rollover crashes. The 

benefit of a large sample masked the effects of multiple vehicles involved in rollover crashes. It 

was found, however, that the presence of more than one vehicle was highly injurious. Further, 

concepts of incidental versus serious planar events might be considered in this type of analysis 

and will be the subject of subsequent technical reports. 

Approximately 20 percent of rollover crashes involved more than one vehicle. In multiplevehicle rollover crashes, the injury rates were nearly double those of single-vehicle rollover 

crashes. This conclusion was based upon 5.8 MAIS 3+F belted multiple-vehicle rollover-crashinjured occupants per 100 belted occupants exposed to multiple vehicle rollover crashes, as 

compared with 2.8 MAIS 3+F belted single-vehicle rollover-crash-injured occupants per 100 

belted occupants exposed to single vehicle rollover crashes, as reported in Digges (2003). 
6

Belt use was highly correlated with MAIS 3+F injury rates among the unejected. The belted 

unejected occupants had a very low frequency and carried a low risk of injury. Conversely, the 

unbelted ejected were vulnerable to MAIS 3+F injury. The disaggregation of the population by 

restraint use and ejection status highlights the detriment of the unejected unrestrained occupants. 

6.2 Crash Configuration and Crash Severity 

Single-vehicle rollover crashes are distinctive and complex events. The introduction of one or 

more vehicles to the crash before or after the rollover can be devastating. 

For planar and rollover crashes, a means to assess planar crash severity was devised. This made 

use of the 1995 coding modifications to delta V reporting in NASS CDS. Prior to 1995, if 

WINSMASH was unable to perform the damage calculation, for qualified crashes based upon 

vehicle damage measurements, then the severity would go unreported. Qualified crashes 

excluded: 

• damage due to rollover; 

• principal direction of force was non-horizontal; 

• collision with a yielding fixed object that broke away early in the collision sequence; 

• vehicle struck an easily movable object; 

• damage was primarily to the undercarriage of the vehicle; 

• vehicle damage was due to gross underride that engaged only the passenger 

compartment; 

• two vehicles involved in an impact never reached a common velocity (sideswipe and 

endswipe); 

• one of the vehicles involved in an impact was a moving, heavy vehicle that incurred 

significant damage; and 

• simultaneous collision of three or more vehicles occurred that could not be separated into 

distinct collisions involving only one or two vehicles. 

In 1995, an estimated delta V parameter was introduced. This provided an estimate of the 

damage to be used especially when assessing the most severe and second most severe events. In 

this analysis, the composite interpretation provided a qualitative means for comparing the 

computer-generated delta V with the estimated delta V. In table 2, the equivalencies used in the 

analysis are included. In comparing the measured deltaV and the estimated delta V, the results 

are nearly identical. For this reason, the aggregated delta V measure was accepted, allowing for 

an enlarged dataset with known values. 
7

Table 2: Analytical Equivalence of Estimated Delta V to Measured Delta V

Estimated Delta V (Planar Crash Severity) Measured Delta V Equivalent 

Low < 24 kilometers per hour 

Medium >= 24 and <=55 kilometers per hour 

High > 55 kilometers per hour 

 Source: NASS CDS, 1995 – 2002 

 Note: This is not an endorsed method by NASS CDS. It is rather an analytical tool used to enlarge the data set based 

 upon comparing measured alone to measured plus estimated results. Note that the WINSMASH algorithm, using vehicle 

 crash measurements, generates measured delta V and estimated delta V is a qualitative crash severity measure assigned 

 based upon researcher experience. 

7 Justification for Inclusion of Belted Unejected Occupants 

Rollover crashes represented about 10 percent of the tow-away crash population. On average, 

roughly 220,000 tow-away rollover crashes occur yearly in the United States, calculated using 

NASS CDS. Approximately, 80 percent of the rollover crashes involve a single vehicle. Of all 

rollover crash occupants, 68 percent of exposed occupants were belted and involved in a singlevehicle rollover crash. Further, among MAIS 3+F injured occupants involved in rollover 

crashes, 24 percent of these MAIS 3+F rollover occupants were belted and involved in a singlevehicle rollover crash. 

Each population was analyzed to ascertain whether the number of roof to ground impacts was an 

adequate measure of severity. It was envisioned that injury risk would increase smoothly as the 

number of roof to ground impacts increased. Due to the scope of this publication, only the belted 

unejected occupants will be considered. Additional information on this population and the 

remaining populations of interest may be found in Eigen (2004). 

7.1 Belted Unejected Occupants Involved in Single-Vehicle Rollover 

Crashes 

The largest rollover subpopulation was composed of belted unejected occupants involved in 

single-vehicle rollover crashes. These occupants presented the greatest opportunity for 

improvement based upon statistical exigencies. For this group, the injury severity increased as 

the number of roof to ground impacts increased. The annualized frequencies are presented in 

table 3, as a backdrop to figures 1 and 2. 
8

Table 3: Annualized Number of Occupants

Sustaining Rollover Crashes, by Quarter Turns 

and Vehicle Body Type

Number of 

Quarter Turn 

Passenger 

Car 

Sports 

Utility 

Vehicle

Van Pick up 

Truck Total 

1 8,318 5,340 2,336 6,900 22,894 

2 33,515 28,397 1,251 10,356 73,519 

3 3,445 2,877 1,322 1,379 9,023 

4 14,487 12,824 711 4,459 32,481 

5 362 526 64 1,090 2,042 

6 9,043 2,600 400 1,774 13,817 

7 20 918 8 236 1,182 

8 6,012 1,515 67 314 7,908 

9 76 56 26 297 455 

10 1,181 70 99 88 1,438 

11 0 0 0 10 10 

12 311 103 30 0 444 

13 0 0 0 0 0 

14 20 13 9 113 155 

15 0 0 0 0 0 

16 0 2 0 40 42 

 >16 0 107 18 5 130 

End-over-End 550 57 74 44 725 

Total 77,340 55,405 6,415 27,105 166,263 

 Source: NASS CDS, 1995 – 2001 

 Note: Annualized seven-year frequency. 

In figures 1 and 2, in rollovers with two roof to ground contacts, coincident with the sixth quarter 

turn, an increase in the occupant injury rate was noted for all passenger vehicles, as well as 

passenger cars alone. This was revisited later in the hard-copy case reviews. 
9

For this subpopulation, the use of roof to ground impacts was a preferred metric. Further, the 

aggregation for the two-plus roof to ground impacts was warranted. Based upon information 

reported in Eigen (2004), added data will be needed to obtain statistical significance for this 

limited population. Significance was found for the entire rollover population when examining 

the relationship between injury severity and roof to ground impacts. 

In figure 3, the injury risk is plotted over the ascending roof to ground impacts. The number of 

roof to ground impacts was a good severity measure for belted occupants involved in singlevehicle rollover crashes, since injury severity increased monotonically with respect to increasing 

roof to ground impacts. It is noted that 48 percent of MAIS 3+F injuries occurred in rollovers 

with more than one roof to ground impact. The increased risk of injury for occupants in vehicles 

experiencing more than two roof to ground impacts was small. 

When examining quarter turns, injury risk increased with ascending quarter turns but owing to 

the small sample size, and upon disaggregating, the quarter turn cell sizes became very small. 

The increase was better defined via roof to ground impacts. The decrease over the fourth 

through eighth quarter turn might have been attributable to the nature of the sample. The NASS 

cases are representative crashes selected not because of the quarter turns but by an algorithm 

subsuming general vehicle and injury characteristics. The increase in risk from two to three roof 

to ground impacts was small thereby allowing the creation of the two plus roof to ground impact 

category. Little was gained by leaving the two, three, and four roof to ground impact categories 

disaggregated. The roof to ground impacts presented a smoothly ascending relationship, as 

sought in an injury severity metric. 

Source: NHTSA/NCSA/NASS CDS, 1995-2001

Figure 1: Percent Involvement for 

Restrained Unejected Passenger Car 

Occupants and Those Sustaining MAIS

0%

25%

50%

75%

100%

1 3 5 7 9 11 13 15 >16 

Number of Quarter Turns

Percentage of Involvement

Occupants

Belt 3+F

Figure 2: Percent Involvement for 

Restrained Unejected Passenger Car 

Occupants and Those Sustaining MAIS 

3+F Injuries, by Number of Quarter Turns

Source: NHTSA/NCSA/NASS CDS, 1995-2001

0%

25%

50%

75%

100%

1 3 5 7 9 11 13 15 >16 

Number of Quarter Turns

Percentage of Involvement

Occupants

Belt 3+F

3+F Injuries, by Number of Quarter Turns
10

7.2 Belted Unejected Occupants Involved in Multiple-Vehicle Rollover 

Crashes 

The inclusion of the belted unejected occupants involved in multiple vehicle rollover crashes was 

dictated by an injury rate twice as high as the single-vehicle case. A disaggregation of the planar 

and rollover crashes was dictated owing to the difference in crash dynamics experienced in each 

type of crash. Pursuant to these findings, the specific occupant injuries were studied and the 

planar crash severity associated with these crashes provided an added measure to a composite 

crash severity metric. 

8 Discussion of Belted Unejected Population 

The previous sections provided an examination of the rollover data and its relevant 

subpopulations pursuant to data extraction and significance testing. The data spanned the years 

1995 through 2001, as previously published. The subsequent sections consider 1995 through 

2002. 

8.1 General Case 

This report presents the first subpopulations, as presented in Eigen (2004): the belted unejected 

rollover occupants 12 and older seated in the outboard front seats involved in a rollover crash. 

This group constitutes approximately 74 percent of the rollover population and 35 percent of the 

MAIS 3+F injured occupants. In subsequent phases, the unbelted unejected population will be 

considered, since they comprise 19 percent of the rollover population and 23 percent of the 

Figure 3: Injury Rate per 100 Exposed for Belted Unejected Front Seat

Age 12+ Occupants with MAIS 3+F Injuries in Single Vehicle Rollovers

by Number of Roof Impacts

Source: NHTSA/NCSA/NASS CDS, 1995-2001

0

5

10

0 1 2 3+

Number of Roof Impacts

MAIS 3+F/100
11

MAIS 3+F injured occupants. The unbelted ejected population is the third group of interest, 

contributing 4 percent of rollover occupants and 33 percent of the of the MAIS 3+F injured 

occupants, with an injury rate of 49.6 per 100 ejected occupants, per Digges (2003). The 

restrained population will be examined from two perspectives: injury rates and HARM analysis 

of pure rollover. 

An increased risk of injury has been shown for the multiple-vehicle rollover crash occupants. 

These crashes were separated into planar and rollover events. Further, the planar events may 

either have constituted a severe or incidental contact. The severe contact was considered an 

impact to which the injuries might be attributed whereas the incidental contact was an impact in 

which the planar event presented little danger to the occupants and the injuries might reasonably 

be attributed to the rollover sequence. Attribution of an injury to a particular event, however, 

was beyond the scope of this report and retained for future study. 

Cases in which a single-vehicle rollover crash occurred without a prior impact with a fixed 

object were selected as surrogates for the case of pure rollover. This was envisioned in keeping 

with constraints of modeling. The HARM analysis allowed a societal cost to be attributed to the 

injuries. The maximum injury was assigned the cost factor. The maximum injury was 

determined based upon a hierarchy of injuries: head/face, neck, spine, thorax, abdomen, lower 

extremity, upper extremity, unspecified body region, and missing values. This hierarchy was 

selected based upon expected injury patterns occurring in rollover crashes and their severity. 

This was not meant to be an endorsement of any given hierarchy but a starting point from which 

other competing hierarchies might be introduced, at the discretion of the analyst. The AIS 3+F, 

owing to injury specification rather than aggregate occupant severity, level was used to 

determine the areas of concern. From this analysis, areas of concern were identified and led to 

case reviews ascertaining physical crash properties and associated injury mechanisms. 

 

8.2 Specific Case: Multiple-Vehicle Rollover Crash Configuration for 

Belted Occupants 

Injury rates in multiple-vehicle collisions were 1.5 times higher than in single-vehicle rollovers, 

per Digges (2003). Among the unejected occupants involved in multiple-vehicle rollover 

crashes, the injury rates were 2.2 times higher than in single-vehicle rollover crashes. Planar 

delta V was used to capture the severity of the planar portion of the crash. 

Two delta V measures were used in this study to determine planar severity, measured delta V 

and estimated delta V. Measured delta V was the value yielded from the WINSMASH algorithm 

based upon vehicle damage. The estimated delta V, for crashes not able to be calculated using 

WINSMASH, was made available starting in 1995. These crashes included, but were not limited 

to, rollover and sideswipe. The estimates carried qualitative values of low, medium, and high 

crash severity. Table 2 provided a translation for the aggregation of these two values. 

Comparisons of delta V by roof to ground contacts were made for all general areas of damage 

and for aggregated rollover crashes. The results when using only measured delta V and 

aggregating measured and estimated delta V yielded the same results. This allowed for the 

following analysis. Results for each of the crash modes and the aggregated case were published 
12

in Eigen (2004). Based upon these results, comparisons of body regions injured by the number 

of roof to ground impacts and the planar crash severity were analyzed. 

In figure 4, the distribution of MAIS 3+F occupant injuries was partitioned, by the number of 

roof to ground contacts and planar crash severity. The injury measure was defined previously to 

account for serious injury. The roof to ground contacts, synonymous with roof to ground 

impacts, were also described previously. The planar severity was introduced to disaggregate 

effects of the rollover and planar events. Figure 5 also contained a similar format, however, 

substituting MAIS 3+F injury distribution with MAIS 3+F injury risk. The injury risk was 

described in both graphics over ascending number of roof to ground contacts or planar crash 

severity. The remaining discussion followed this tact by disaggregating the injury severity and 

referencing the salient rollover and planar measures of crash severity. 

Continuing with the discussion of figure 5, an evident increase was identified over the increasing 

planar severities for each level of roof to ground impact. The injury risk also increased with 

increasing roof to ground contacts for low and medium planar severity. A general increase in 

risk was found with damage extent and roof to ground contacts. The zero roof to ground impacts 

category was found to have an outlier potentially from a severe event or limited amount of data. 

This condition was primarily associated with severe side impacts that resulted in one quarter 

turn. Additional years of crash data might increase the sample and allow for the conditions of 

the outlier to be more completely identified. 

Source: NHTSA/NCSA/NASS CDS, 1995-2002

Zero One Two

Plus

low

med

high

0%

5%

10%

15%

20%

25%

30%

MAIS 3+F Distribution

Number of Roof Impacts

Planar Severity

Figure 4: Percentage of Injury, by Planar and Rollover Severity

low med high
13

As expected, the majority of MAIS 3+F injury percentage distribution falls within the first roof 

to ground contact. As noted previously, the rollover component was not assigned a delta V 

reading owing to the algorithm architecture. The linear deformation present in planar crashes 

was absent in rollover crashes since the forces were not directly proportional to deformation. 

Delta V was used as the planar severity indicator. Based upon the studies cited above, roof to 

ground impacts have been selected as the rollover severity indicator. From this point, a mixed 

indicator evolved. The planar crash severity was dependent upon energy transfer, whereas the 

number of quarter turns sustained by the vehicle constituted the rollover severity indicator. Roof 

deformation does not predict the amount of crash energy. 

8.3 Analytical Considerations 

Among belted occupants, several refinements should be made in analyzing rollover crashes and 

defining severity. Definitions would reflect the findings of the data analysis to include multiplevehicle collisions, fixed-object contacts, and roof leading, one-quarter-turn rollover crashes. 

For multiple-vehicle collisions occurring prior to rollover, a pre-rollover crash severity measure 

must be defined with a rollover severity measure. In the previous discussion, delta V was 

proposed owing to its accessibility and the introduction of the estimated value for the delta V. 

The dataset was enhanced by including measured and estimated delta V. This was warranted 

based upon the analysis described previously. 

The condition of fixed object contacts, especially for single-vehicle crashes, presented unique 

scenarios. As was seen in hard-copy case review, multiple-impact crashes constituted an 

elevated danger, per the work of Bahouth (2004). 

The final condition identified for the belted occupants was the rollover interrupted at the first 

quarter turn. In this roof-leading scenario, great force was being imparted to the vehicle. It was 

suggested that some coding element be introduced to easily identify this condition. 

Figure 5: Injury Risk, by Planar and Rollover Severity

Source: NHTSA/NCSA/NASS CDS, 1995-2002

Zero One

Two

Plus

low

med

high

0

10

20

30

40

50

60

MAIS 3+F/100

Number of Roof 

Impacts

Planar Severity

low med high
14

9 Societal Cost of Injuries to Belted Unejected Occupants 

Involved in Single-Vehicle, Nonfixed Object Rollover 

Crashes 

The largest segment of the injured population was found to be the belted unejected occupants. 

Although they constituted a lower injury risk than their unbelted counterparts, their absolute 

magnitude and their willingness to comply with restraint-use mandates made them a very 

interesting group. These occupants have benefited from a technology intended for planar crashes 

and, in most instances, they fared very well. Cases where occupants have opted to comply but 

have been injured merited further investigation. 

A further refinement of this population excluded multiple-vehicle crashes or any crash in which a 

collision with a fixed object preceded the rollover crash. In this way, unusual, violent conditions 

imposed by fixed-object crashes would not confuse the pure rollover scenario. 

9.1 Description of Chosen Societal Cost Method – HARM 

The societal cost of injuries has long been a topic of interest. This has aided in benefit cost 

analysis for the preparation of rulemaking, research, and development. Analysis and methods 

developed by Malliaris (1982) have become the basis for such costing. The methodology 

involved the examination of overall societal costs of injuries attributable to motor vehicle 

crashes. The injury severity for HARM was based upon the average costs of injured people at 

each MAIS level. The HARM was expressed in dollars. NHTSA subsequently modified the 

calculation by dividing the cost by the average cost of a fatality. The resulting HARM was 

expressed in equivalent fatalities. To calculate HARM for a population, the maximum severity 

of each injured occupant was multiplied by the HARM factor (in equivalent fatalities) and the 

results for the population were added together. The HARM provided an overall cost of injuries 

of different severities in terms of equivalent fatalities. 

HARM factors were applied to each injury and the maximum injury sustained by each occupant 

to obtain proportional costs. Analysis was performed using both methods but the former might 

tend to overstate injury cost. The benefit rested with the larger data set able to report injuries 

more completely. The latter method was developed upon assignment of a maximum injury 

based upon a hierarchy. The hierarchy was defined in descending order as follows: head and 

face, neck, spine, thorax, abdomen, lower extremities, upper extremities, unspecified, and 

missing values. Only AIS 3+F injuries were considered in this study. Results for each AIS level 

were reported in Eigen (2004). 

9.2 Results Leading to Case Reviews 

The case review parameters were selected based upon comparative data from each of the AIS 

levels and characterized in figure 6 for AIS 3+F for restrained occupants. In this figure, the 

percentage of HARM was reported by injured body region and number of roof to ground 

impacts. Two body regions emerged as the areas of concern within pure rollover crashes when 

studying the maximum injuries, as defined by the rollover injury hierarchy. 
15

The majority of head injuries occurred in rollovers with one roof to ground contact. This was 

coincident with findings of Burel (2003). The model of an SUV in a maneuver induced rollover 

provided insight into the time at which head velocity was the highest for the left and right front 

belted unejected occupants. The head velocities reached a maximum of about 5 meters per 

second after the first roof to ground contact. In that research, the maneuver-induced rollover was 

likened to a pure rollover condition. This occurred in the absence of any fixed object or other 

vehicle engagement. Among restrained occupants sustaining head injuries, the HARM was 

second only to those occupants sustaining chest injuries at two plus roof to ground impacts. 

Head injuries were not disaggregated with regard to intruding components; therefore, these 

injuries may or may not have been related to roof intrusion. 

Chest injuries were most prevalent at two or more roof to ground impacts, as shown in figure 6. 

The elevated thoracic injuries were unexpected and warranted case reviews. An engineering 

analysis of the possible crash mechanisms and injury sources was undertaken. The summarized 

photographic and occupant injury analyses results were presented in the next section. The 

complete text was published in Eigen (2004). 

Figure 6: Percentage of HARM, by Number of Roof Impacts and Most

Seriously Injured Body Region

Source: NHTSA/NCSA/NASS CDS, 1995-2002

Zero One Two

Plus

Head

Thorax/Abd

Spine

Extrem

0%

2%

4%

6%

8%

10%

12%

14%

Percentage of HARM

Number of Roof 

I t

Injured Body 

Region, Maximum 
16

10 Identification of Case Review Focus 

Based upon their HARM contribution as seen in figure 6, the prevalence of chest injuries 

pursuant to high-severity crashes was evident. The severity, in this case, was the early measure 

of quarter turns. In general, high tripping was often associated with the two-plus roof to ground 

impacts. This was particularly true for passenger cars. The static stability factor for this vehicle 

type ranged from 1.30 to 1.50, indicating a high degree of force to sustain the vehicle through 

more than six quarter turns and the damage patterns found. The near-side and far-side rollover 

had distinct chest injury sources. For the near-side rollovers, the most frequent injury source was 

side hardware; for far-side rollovers, the most frequent injury source was the safety belt. The 

near-side was selected for this summarization owing to the photographs and data associated with 

the case and their exemplification of the side force phenomena. Additional information on farside crashes was published in Eigen (2004). 

Approximately, 190 cases were reviewed. These cases were qualified based upon MAIS 3+F 

injuries sustained by the left- or right-front belted occupant who was at least 12 years old 

involved in a rollover crash. From these cases, the zero, one, and two-plus roof to ground impact 

cases were separated. Among each roof to ground impact group, the injuries to body region 

provided the final division. 

10.1 Four Illustrative Tripping Damage Cases – High Side Force 

Review of cases lead to the identification of high side forces. These were identified based upon 

severe near-side wheel damage and two-plus roof to ground impacts. Further, near-side injuries 

to restrained, unejected occupants were generally attributed to a side interior contact and resulted 

in rib fractures and lung injuries. This followed the early findings indicating that thoracic 

injuries over two or more roof to ground impacts were major contributors to the overall HARM 

attributable to injuries of the highest severity per occupant, as shown in figure 6. Among the 

restrained, unejected occupants, a sharp increase in MAIS 3+F injuries was noted in rollovers 

with two or more roof to ground contacts, per figures 1 and 2. 

10.1.1 Case 2001–78-20 

The case vehicle, a 1997 Buick Riviera, was traveling in a westerly direction. It experienced a 

trip-over at the roadside, rolled to the left, and came to rest after six quarter turns. This driverside-leading rollover occurred pursuant to a departure on the right side of the roadway, per figure 

7. The sole occupant was an 86-year-old male driver. He experienced left aspect AIS 3 rib 

fractures on the right and left sides of the rib cage and a left aspect AIS 3 lung injury with 

unknown details. The injuries were attributed to the left side vehicle interior. 
17

As noted, this was a left side leading rollover crash. Figure 8 depicted the near-side wheel 

damage as evidence of the high side force. The left front and rear wheels were severed from 

their respective axles during the crash, highlighting the severity of the crash. 

Figure 7: Case 2001-78-20 Scene Diagram and Crash Summary 

Source: NHTSA/NCSA/NASS CDS, 2001 
18

Figure 8: Case 2001-78-20 Indication of Side Force 

Source: NHTSA/NCSA/NASS CDS, 2001
19

10.1.1 1998–45–54 

The case vehicle, a 1997 Chevrolet Geo Prism, was traveling in a westerly direction and departed 

the right side of the roadway, as seen in figure 9. It rotated clockwise and was tripped over at the 

roadside by the ground (possibly on loose dirt, gravel, etc.) The vehicle rolled six quarter turns 

toward the left in a driver side leading rollover crash. The driver, a 40-year-old female, 

sustained left aspect AIS 3 rib fractures with hemothorax, a collection of blood in the pleural 

portions of the thoracic cavity, and pneumothorax, an accumulation of air or gas in the thoracic 

cavity. These injuries were attributable to the side interior. 

In figure 10, the high side force was evident in the front wheel and axle structure. The wheel 

bent away from the front axle on the near-side of the rollover crash. The severity was 

accentuated as seen by the bending at the B-pillar. 
20

Figure 9: Case 1998–45–54 Case Summary and Scene Diagram 

Source: NHTSA/NCSA/NASS CDS, 1998
21

Figure 10: Case 1998–45–54 Indication of Side Force 

Source: NHTSA/NCSA/NASS CDS, 1998
22

10.1.3 Case 1998–75–92 

The case vehicle, a 1990 Jeep Cherokee, was traveling in an eastbound direction. It hydroplaned 

and lost control, departing the left side of the roadway, per figure 11. The case vehicle reentered 

the roadway and rolled to the left eight quarter turns. The vehicle tripped over the ground 

(possibly on loose dirt, gravel, etc.). The driver, a 53-year-old male, sustained left aspect AIS 3 

rib fractures with hemothorax and pneumothorax. 

As noted previously, this phenomenon primarily affected passenger cars; however, some SUVs 

and pickup trucks underwent similar, high side force rollover crashes producing chest injuries, as 

seen in figure 12. The left rear near-side wheel was severed from the axle. Upon very close 

examination of the case photographs for the left front near-side, wheel damage was evident at the 

top near the point where the tire lost contact with the wheel. 
23

Figure 11: Case 1998–75–92 Case Summary and Scene Diagram 

Source: NHTSA/NCSA/NASS CDS, 1998
24

Figure 12: Case 1998–75–92 Indication of Side Force 

Source: NHTSA/NCSA/NASS CDS, 1998
25

10.1.4 Case 1999–41–24 

The case vehicle, a 1999 Chrysler 300M, was negotiating a right-hand curve in an eastbound 

direction, per figure 13. The case vehicle traveled down an embankment, rotated clockwise, and 

tripped at the shoulder/unpaved area. The ground (possibly loose dirt, gravel, etc.) was cited as 

the object contacted preceding the rollover. The vehicle rolled to the left ten quarter turns, in a 

driver-side-leading rollover crash. The driver, a 62-year-old male, sustained an AIS 5 bilateral 

rib cage flail chest, an AIS 3 bilateral pleura laceration with hemothorax and pneumothorax, and 

a right aspect AIS 3 unilateral lung laceration. In this near-side engagement, the steering column 

was cited as the injury source. The AIS 5 injury was the medically reported cause of death. 

Figure 13: Case 1999–41-24 Case Summary and Scene Diagram 

Source: NHTSA/NCSA/NASS CDS, 1999
26

In figure 14, a very high tripping force was evident, sustaining the rollover through ten quarter 

turns. As noted previously, it takes great force to initiate the rollover of a passenger car and even 

greater force must be present to sustain it through ten quarter turns. The high side force was 

evident in the bent wheel at the front. Further, the wheel was severed from the axle at rear nearside of the rollover crash. 

Figure 14: Case 1999–41-24 Indication of Side Force 

Source: NHTSA/NCSA/NASS CDS, 1999
27

10.2 Pre-Rollover Complex Motion 

In the next segment pre-rollover events were disaggregated to define planar and rollover events. 

Further, incidental versus severe planar contacts were considered in describing the crash and the 

potential attribution of injuries to planar versus rollover events. These injury parameters may be 

useful in refining a severity metric and will be the subject of future work. Although Bahouth 

(2004) did not consider rollover crashes, the multiple-impact metric was found to hold true in 

cases where a planar event was followed by a rollover crash. 

 

10.2.1 Case 1998–11–223 

The case vehicle, a 1985 Pontiac Grand Am, was traveling northbound and departed the left side 

of the roadway, as seen in figure 15. It was redirected back on to the roadway by the guardrail. 

It proceeded to bounce over the guardrail and rolled over six quarter turns at the roadside. The 

driver, a 31-year-old female, sustained left aspect AIS 3 rib fractures with pneumothorax and a 

left aspect AIS 3 unilateral lung contusion, attributable to the side interior. It was suggested that 

a pre-impact change in direction might have contributed to the injury. This complex pre-crash 

motion was also postulated to have been a severe planar contact indicating that the injuries might 

have been sustained prior to the rollover crash. 

Subsumed within the scenario of complex motion, evidence of high force continued to exist, per 

figure 16. Noteworthy, however, was the violence of the planar component of this crash, which 

upon examination may have been responsible for the injuries sustained by the driver. The severe 

side force of the rollover crash was inescapable owing to the repeated impact on the left side 

(rollover initiation side) over the two roof to ground impacts. In the absence of the planar 

component, neither was it known nor would it have been appropriate to speculate whether these 

injuries would have been minimized or other types of injuries might have been produced. The 

redirection, however, was the event that preceded the rollover sequence. 
28

Figure 15: Case 1998–11-223 Case Summary and Scene Diagram 

Source: NHTSA/NCSA/NASS CDS, 1998
29

Figure 16: Case 1998–11-223 Indication of Side Force 

Source: NHTSA/NCSA/NASS CDS, 1998
30

10.3 Discussion of Case Review Results 

The case reviews allowed for detection of vehicle damage patterns and injury patterns. The 

photographic analysis permitted concepts not readily available via coded data to be identified. 

The high side force was found to be associated with two-plus roof to ground impact crashes 

inducing chest injuries. A further refinement was the identification of near-side versus far-side 

orientation in injury patterns. The orientation was dependent upon the occupant seating position 

and the side of initiation for the rollover crash. The near-side, multiple-roof to ground-impact 

rollover crash generally resulted in thoracic injuries attributable to the side interior. In contrast 

the far-side, multiple-roof to ground-impact rollover crash, generally resulted in safety-beltinduced thoracic injuries. Conclusively, it can be said that a great deal of force was required to 

sustain vehicles through high numbers of roof to ground impacts. This was evidenced by the 

wheel deformation therefore making the association with the chest injuries more tenable. 

10.4 Qualitative Results of Individual Case Analysis 

Tripping damage was found to be indicative of chest injuries and higher number of roof to 

ground impacts. Further, the pre-rollover events that influence injury outcome were found to be 

complex skidding and spinning motions and impacts with fixed objects and vehicles. In the 

multiple-vehicle and/or multiple-event rollover crashes, this allowed for disaggregation of the 

planar event. The planar event could be viewed as an injury producer, severe planar contact, or 

incidental contact, where the rollover crash was culpable for injuries sustained. Within the larger 

study, cases existed of crashes where injuries might have been caused both during the planar and 

rollover events. This is a highly exploratory enterprise dependent upon the experience of the 

analyst and was devised as a means to stimulate more research in this field. 

11 Computer Modeling 

In order to amplify any study and supplement scanty test data, computer modeling has become 

an accepted tool. In the case of rollover crashes, however, little data existed for the replication of 

vehicle tripping at the time of rollover. Owing to the scarcity of data, speculative inputs were 

used in modeling. Based upon this data many assumptions must be made. 

11.1 Discussion of Modeling Results 

From the tripping acceleration test data presented in Digges (2004) and seen in figure 17, it was 

possible to obtain a crash pulse. The test data reached nearly 14 g’s, producing nearly 25 g’s 

output. For chest injury to occur, 25 g’s has been found to be sufficient. Little other test data 

existed; therefore, many assumptions were made for modeling. 

 
31

Figure 17: Y Acceleration - Input for MADYMO Simulation 

Source: Digges, 2004

Using MADYMO, a model was created using the force inputs. This was done to clarify some of 

the injury forces. According to the model, a 2,500 Newton force was reached, as described by 

Dahdah (2004) and reproduced in figure 18. This was considered sufficient to induce chest 

injury, especially for the elderly population. 

Y acceleration (g's)

0

2

4

6

8

10

12

14

0

0.961.922.883.84

4.8

5.766.727.688.64

9.6

10.611.512.513.414.415.416.317.318.219.220.221.122.1

232425

25.926.927.828.829.830.731.732.633.634.635.536.537.438.439.4

Time (ms)

G's

Y acceleration (g's)
32

11.2 Observation Based upon Modeling – Tripping Acceleration 

Tripping acceleration was found to be an important factor in rollover crash severity. It was 

postulated to influence the number of roof to ground impacts. The reviewed cases provided a 

link between chest injuries and the tripping severity. A paucity of crash pulse data existed, as 

much of this was proprietary and held by manufacturers and suppliers of air bags. This effort 

was required for modeling effects but hampered by the proprietary nature of the data. Further, 

structural force-deformation response data must be added to the model for prediction of severity 

based upon field measurements. 

Figure 18: Door Forces Generated by MADYMO Simulation 

Source: Dahdah, 2004 

Door Forces (N)

0

500

1000

1500

2000

2500

0.000.561.121.682.242.803.363.924.485.045.606.166.727.287.848.408.969.52

10.0810.6411.2011.7612.3212.8813.4414.0014.5615.1215.6816.2416.8017.3617.9218.4819.0419.60

Time (ms)

N

Door Forces (N)
33

12 Conclusions 

 

Conclusions are provided for the following subtopics: 

• rollover population selection; 

• crash configuration and its influences on occupant outcome; 

• application of societal costs to injuries sustained by restrained unejected occupants in 

rollover crashes; and 

• association of prevalent crash modes and injury characteristics for restrained unejected 

occupants. 

12.1 General Conclusions Based upon Previous Work 

• Number of roof to ground contacts is a good aggregation of quarter-turns for measuring 

rollover severity. 

The following considerations or exceptions exist when considering roof to ground 

contacts: 

o quarter turns can be more severe due to planar impacts; 

o impacts to fixed objects with roof leading; 

o severe side and frontal crashes with other vehicles; and 

o end-over-end rollovers. 

• Inclusion of planar crash severity (delta V) prior to rollovers in addition to the rollover 

severity (number of roof to ground contacts) improves understanding of the rollover 

crash. 

• The magnitude of the trip pulse influences the number of roof to ground impacts and may 

increase AIS 3+ chest injury risk 

• Most MAIS 3+ head injuries occur in rollovers with one roof to ground contact. 

Computer modeling indicates the highest head velocity can occur at that time. 

12.2 Rollover Population Selection 

The early sections of this publication guided the selection of crashes for detailed review. These 

included the rationale for their selection based upon frequency and injury rate. The populations 

of interest were found to be unejected belted, unejected unbelted, and ejected unbelted 

occupants. This phase of study and the current publication focused on the unejected belted 

occupants owing to their prevalence and their contribution to serious injury. 

12.3 Crash Configuration and Its Influence on Occupant Outcome 

Disaggregating rollover crashes by crash configuration and restraint use was the next portion of 

the analysis. Crash configuration was determined by single-vehicle or multiple-vehicle 

involvement in the rollover crash. Among belted rollover crash occupants, occupants involved 

in multiple-vehicle crashes sustained injury rates twice as high as those for occupants involved in 

single-vehicle crashes. 
34

12.3.1 Application of Societal Costs to Injuries Sustained by Restrained 

 Unejected Occupants in Rollover Crashes 

The percentage contribution of HARM was used to describe the societal cost of injuries to the 

restrained unejected occupants. Rollover crashes similar to the pure rollover case were selected 

by excluding fixed-object contacts before the rollover crash. Occupants were selected based 

upon an overall MAIS 3+F injury severity and their most severe injury was selected based upon 

a hierarchy of injuries. HARM for AIS 3+F injuries highlighted the head and thorax injuries at 

one roof to ground impact and two-plus roof to ground impacts, respectively. 

12.3.2 Association of Prevalent Crash Modes and Injury Characteristics for 

 Restrained Unejected Occupants 

Based upon the results of the HARM analysis for the pure rollover case, the head and thoracic 

injuries were identified as areas of concern. Head injuries have traditionally posed a singular 

problem for rollover crashes and modeling work complemented the findings of the HARM 

analysis. The thoracic injuries warranted extra study owing to the high number of quarter turns 

and the type of vehicles involved. High tripping acceleration was the physical phenomenon 

associated with these thoracic injuries. These were also studied with regard to crash orientation, 

finding that thoracic injuries pursuant to a near-side rollover crash were attributable to the side 

interior, per injury source reporting in NASS CDS. Finally, computer modeling also provided 

some basis for the concern over thoracic injuries. 
35

13 Recommendations 

13.1 Future Work Recommendations 

• Continue analysis to obtain statistical significance for all observations. 

• Perform further research on tripping acceleration. 

• Obtain pulses via crash testing. 

• Obtain damage versus force response via static or dynamic testing. 

• Provide field measurements of tripping damage. 

• Develop/Perform severity calculations like WINSMASH. 

• Continue examination of roof to ground impact injury mechanisms. 

13.2 Recommendations for NASS Researchers 

• Continue collecting number of quarter turns and estimated planar delta V; these were 

very valuable to analysis. 

• Enhance documentation of tripping damage with photography and measurements. 

• Identify cases with one quarter turn in which the severity was increased by: 

o Roof leading fixed impact 

o Pre-rollover planar crash 

13.3 Recommendation for Rollover Data Analysts 

• Aggregate quarter turns by number of roof to ground impacts. 

• Disaggregate data by: 

o ejected and unejected; 

o belted and unbelted; 

o single-vehicle and multiple-vehicle rollovers; and 

o severe versus incidental planar contact. 

• Augment data analysis with hard copy case reviews and computer modeling. 

 
36

14 References 

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Burel, J., “Dynamic Analysis of Occupant Behavior in Vehicle Rollover Event,” The George 

Washington University, Ashburn, 2003. 

Dahdah, S., “Effects of Roll Rate and Tripping Velocities on Occupant Kinematics in Vehicle 

Rollover,” The George Washington University, Ashburn, 2004. 

Digges, K., and Eigen, A., “Crash Attributes That Influence the Severity of Rollover Crashes,” 

Proceedings of the 18th ESV Conference, No. 231, Nagoya, 2003. 

Digges, K., Burel, J., Godrick, D., Soltani, H., Bedewi, P., and Eigen, A., “Crash Simulations to 

Understand Injury Mechanisms in Maneuver-Induced Rollover Crashes,” Proceedings of SAE 

(2004), no. 2004-01-0330. 

Eigen, A., “Characterization of Attributes Applicable to a Rollover Crash Severity Metric,” The 

George Washington University/NHTSA, Ashburn 2004. 

Eigen, A., “Examination of Rollover Crash Mechanisms and Occupant Outcomes,” DOT HS 809 

692, Washington, DC, 2003. 

Hitchcock, R., Malliaris, A.C., and Hedlund, J., “A Search for Priorities in Crash Protection,” 

Proceedings of Society of Automotive Engineers, SAE SP-513 (1982), 1–33. 

McGuigan, R., “The Severity of Rollover Crashes,” Tech Report, DOT HS 805 883, National 

Center for Statistics and Analysis, NHTSA, Washington, DC, 1980. 

Najjer, D., “The Truth About Rollovers,” Tech Report, DOT HS 805 883, National Center for 

Statistics and Analysis, NHTSA, Washington, DC, 1980. 

NHTSA, National Center for Statistics and Analysis, “2000 NASS Injury Coding Manual,” 

Washington, DC, 2000. 
37
NHTSA’s National Center for Statistics and Analysis 400 Seventh St., SW., Washington, DC 20590

DOT HS 809 894 

November 2005 

NHTSA’s National Center for Statistics and Analysis