National Center for Statistics and Analysis 400 Seventh St., S.W., Washington, D.C. 20590

December 2003 DOT HS 809 692

Traffi c Safety Facts

Research Note

Examination of Rollover Crash Mechanisms and 

Occupant Outcomes

Ana María Eigen *

Objective

In response to the growing 

concern surrounding rollover 

incidence and its consequences, 

the present analysis seeks to 

answer the following questions:

! Which are the most 

prevalent rollover crash 

attributes?

! What is the injury outcome 

for rollover crash occupants?

Background

A void in real-world rollover data 

compilation was fi lled in 2002 with 

the release of “Characteristics of 

Fatal Rollover Crashes” (DOT HS 

809 438.) Using the Fatality 

Analysis Reporting System 

(FARS), DOT HS 809 438 

examined an important segment 

of the rollover population. It was 

shown in the referenced report 

that, generally, those without 

restraint and subject to ejection 

are the most vulnerable.

This Research Note seeks to 

expand on the fi ndings of the DOT 

HS 809 438 by using the National 

Automotive Sampling System 

(NASS) – Crashworthiness Data 

System (CDS.) Combining the 

crash investigation elements 

with the injury reporting inherent 

to this data base, a more exact 

description of the crash is 

possible.

In 2003, NHTSA has declared 

the issue of passenger vehicle 

rollover a priority, owing to 

its prominence in fatal crash 

statistics. The agency has been 

active in the implementation 

of the Rollover Resistance 

Rating for new vehicles and in 

the development of a dynamic 

rollover test.

While, the number of quarter 

turns is not always accepted as 

a measure of rollover severity, 

it has been used in prior works 

such as Rains and Kanianthra 

(SAE 1995.) In this analysis, it 

will be used as a comparative 

measure aimed at discerning 

rollover crash attributes and 

associated injury vulnerabilities. 

Based on previous reporting, 

the unbelted occupant is the 

most vulnerable to ejection and 

fatality; however, even the belted 

occupant is at risk because 

some current seatbelts, and 

most retractors, are primarily 

designed to withstand the 

exigencies imposed by a planar 

crash. Further, the complexity 

of the rollover crash suggests 

that vehicle integrity, in particular 

roof strength, in conjunction 

with, restraint use must provide 

adequate protection to minimize 

occupant injury. The concern 

is accentuated by recent roof 

crush testing (Federal Highway 

Administration, Test 03005 

A&B, 2003) in which each roof 

strike appeared to weaken the 

loading capacity of the roof. 

The examination of the most 

frequently occurring types 

of rollover crashes and their 

associated injury outcomes 

in relation to quarter turns, 

as reported in real-world data 

bases, is proposed to further 

understand rollover crashes.

Introduction

From 1995 through 2001, an 

estimated 17.1 million (weighted) 

crashes, involving passenger 

vehicles towed from the scene 

due to damage sustained in the 

crashes, occurred on roadways 

in the United States. Of these 

17.1 million crashes, 4.5 million 

were single vehicle events. 

Approximately 28 percent of 

these single vehicle crashes 

resulted in rollovers, as reported 

in the NASS – CDS. Among all 

rollover crashes (1.6 million), 

81 percent were single vehicle 

encounters.

Among rollover crashes reported 

in NASS - CDS, approximately 

55 percent ended in one or two 

quarter turns contacting either 

the near side of the roll or the 

roof. Generally, these crashes 

*Ana María Eigen is a Mechanical Engineer with the Mathematical Analysis Division of the National Center for Statistics and Analysis, NHTSA.
National Center for Statistics and Analysis 400 Seventh St., S.W., Washington, D.C. 20590

occurred when the vehicle left 

the roadway and encountered a 

tripping mechanism such as soft 

dirt or loose gravel. In contrast, it 

was noted that untripped rollover 

crashes comprised only a small 

fraction of all rollover crashes 

and were differentiated from the 

tripped cases by the absence of 

any tripping mechanism.

Under the circumstances 

encountered during a rollover 

crash, occupant vulnerability 

increased with the omission 

of restraint use. For those 

completely ejected, 97 percent 

were unrestrained. Among 

injured occupants, the proportion 

of serious injuries was greater 

for those involved in rollover 

crashes.

Defi nitions and Constraints

In order to amplify the scope of 

rollover crash understanding, 

the NASS – CDS was queried. 

CDS is a nationally representative 

sample of tow-away crashes 

based on Police Accident 

Reports (PAR). Upon selection, a 

comprehensive crash scene and 

vehicle review combines with the 

occupant demography and injury 

account to form the case fi le.

Passenger vehicle (passenger 

car, sport utility vehicle, van, and 

pickup truck) crashes reported in 

CDS from 1995 through 2001 

were considered in this study.

Rollover Crash Mechanism

Percentage of Rollover Crashes, by Crash 

Confi guration and Fleet Composition

From 1995 through 2001, 

single vehicle rollovers accounted 

for 81 percent of all rollovers. As 

seen in Table 1, passenger cars 

experienced 50 percent of single 

vehicle rollovers. Polk vehicle 

registration data aggregated over 

1995 through 2001, yielding 

vehicle years, indicated that 65 

percent of the 1.54 billion vehicle 

years belonged to passenger 

cars. The remaining fi fty percent 

of the single vehicle rollover 

crashes were attributable to light 

trucks; however, this vehicle class 

comprised 35 percent of the 

vehicle fl eet. The vehicle years 

were aggregated in response 

to the small CDS sample size. 

It was not dictated by the fl eet 

composition, which experienced 

rapid changes over this period.

Rollover Initiation Object

The predominant tripping 

mechanism inducing rollovers in 

single vehicle crashes tends to 

be ground (61 percent of single 

vehicle rollover crashes.) In CDS, 

if the rollover initiation type has 

been identifi ed as a fall-over, 

neither tripped nor untripped, 

or turn-over, an untripped 

situation, rollover initiation object 

aggregates these attributes. It 

should be noted that these are 

very different types of rollover 

crashes. Further, the rollover 

initiation type fall-over constitutes 

most of the entries found in this 

aggregated attribute. Please 

reference the Section “Rollover 

Initiation Type” for disaggregation 

of these two attributes.

Among multi-vehicle rollover 

crashes, the vehicle is the 

predominant tripping mechanism, 

accounting for 47 percent. Thirtyfour percent of multi-vehicle 

rollover crashes occur owing to 

tripping on the ground.

Table 1

Percentage of Vehicles in Single Vehicle Rollover by Body Type 

and Type of Rollover (Sample sizes given in parentheses. Total column given in 

thousands, weighted)

 

 1 2 3+ Unknown

Vehicle Quarter Quarter Quarter End- Num. of (in 

Body Turn Turn Turn over- Quarter ‘000)

Type (Lateral) (Lateral) (Lateral) End Turns Total

Pass. 13 % 42 % 40 % 1 % 4 % 632

Car (n=144) (n=499) (n=719) (n=43) (n=107) 50 %

SUV 13 % 41 % 40 % 0 % 6 % 330

 (n=108) (n=127) (n=384) (n=6) (n=58) 26 %

Van 31 % 22 % 42 % 1 % 3 % 44

 (n=38) (n=25) (n=78) (n=2) (n=7) 3 %

Pickup 22 % 35 % 39 % 0 % 4 % 261

 (n=95) (n=134) (n=328) (n=10) (n=32) 21 %

Total 16 % 39 % 40 % 1 % 5 % 1,268

 (n=385) (n=785) (n=1,509) (n=61) (n=204) 100 %

Note: Slight differences may exist in percentage calculations owing to rounding.

Source: NCSA, NHTSA, NASS-CDS,1995-2001
National Center for Statistics and Analysis 400 Seventh St., S.W., Washington, D.C. 20590

stopping and induced by contact 

with a curb, pothole, wheel rim/

pavement contact, or pavement/

soil dug into by a vehicle’s wheels. 

At each of the quarter turn levels 

the trip-over is predominant. 

The fall–over is the second most 

prevalent event occurring in 13 

percent of the single vehicle 

rollover crashes. As defi ned by 

the CDS coding manual, in fallover, the vehicle is tipped by a 

slope so that its center of gravity 

is outboard of its wheels. It should 

be noted that this defi nition is true 

for a vehicle not in motion. For a 

moving vehicle, the dynamics 

of the vehicle are controlled by 

gravity and centrifugal forces.

Number of Quarter Turns

In the single vehicle rollover 

crash, most vehicles come to 

rest at two quarter turns. This 

can be a promising sign once the 

rollover has occurred for several 

reasons. First, if the roof meets 

the required standard, it should 

withstand the mass of the vehicle. 

Second, the roof has not been 

debilitated with repeated strikes 

since the vehicle undergoes two 

quarter turns and comes to rest. 

Finally, since undue force has not 

been exerted during the fi rst roof 

strike the windshield will generally 

be intact. This is signifi cant 

because the windshield is an 

important structural element 

for roof integrity/strength, as 

shown by the work of Henderson 

and Paine (1998.) Most of these 

benefi ts are severely curtailed 

if the occupant omits restraint 

use.

Sixty-four percent of multi-vehicle 

rollovers last up to two quarter 

turns, as compared to 55 

percent in the single vehicle case. 

Since only 19 percent of rollover 

crashes involve more than one 

vehicle, fewer conclusions may 

be drawn than from the single 

vehicle scenario. Additionally, 

single vehicle rollovers are very 

complex and unique events; the 

presence of more vehicles, in 

the multi-vehicle rollover case, 

serves to further obfuscate the 

event and hamper reconstruction 

of the crash relevant to injury and 

damage.

Rollover Initiation Type

The results for this variable 

are included for completeness; 

however, data prior to 1997 are 

subject to recodifi cation based 

on methodologies proposed by 

Hertz (1999). Of specifi c concern 

and warranting additional study 

are the vehicles that experience 

off-paved road excursion and 

rejoin the paved roadway. Upon 

publication, CDS data sets are 

not revised, therefore, the work 

of Hendriks (1998) and Hertz 

(1999) provide an update to 

the attributes relevant to this 

variable. The summarization 

below is limited to 1998 through 

2001.

The trip–over (tripped rollover) 

is the rollover initiation type 

most commonly experienced (71 

percent) during single vehicle 

rollover crashes, per Table 2. 

This scenario is enacted by a 

sudden sideways slowing or 

Table 2

Percentage of Vehicles in Single Vehicle Rollover by Rollover Initiation 

Type and Type of Rollover

(Total column given in thousands, weighted)

 

 1 2 3+ Unknown

Rollover Quarter Quarter Quarter End- Num. of (in 

Initiation Turn Turn Turn over- Quarter ‘000)

Type (Lateral) (Lateral) (Lateral) End Turns Total

 

TRIP- 12% 43% 45% 0% 0% 562

OVER 71%

FLIP- 23% 47% 30% 0% 0% 44

OVER 6%

TURN- 71% 19% 10% 0% 0% 27

OVER 3%

CLIMB- 19% 29% 52% 0% 0% 9

OVER 1%

FALL- 19% 62% 19% 0% 0% 104

OVER 13%

BOUNCE- 32% 47% 21% 0% 0% 31

OVER 4%

COLLISION 6% 82% 12% 0% 0% 7

W/VEH 1%

OTH ROLLOVER 2% 69% 28% 0% 0% 4

TYPE 0%

END- 0% 0% 0% 0% 100% 4

OVER-END 0%

Total 128 357 304 0 4 793

 16% 45% 38% 0% 0% 100%

Note: Slight differences may exist in percentage calculations owing to rounding.

Source: NCSA, NHTSA, NASS-CDS, 1998-2001
National Center for Statistics and Analysis 400 Seventh St., S.W., Washington, D.C. 20590

Fifty-one percent of multivehicle rollover crashes occur 

as a result of the collision with 

another vehicle. This indicates 

that another vehicle rather 

than a roadway element serves 

to precipitate the event. This 

is followed by the trip-over in 

38 percent of the multi-vehicle 

rollovers.

Direction of Initial Rollover

Approximately, 45 percent of 

vehicles roll to the right and 

55 percent to the left in single 

vehicle crashes. A nearly equal 

proportion exists in multivehicular confi gurations.

Tripping Location on the Vehicle

For most rollover crashes, the 

wheels/tires are the point where 

the initial tripping force occurs 

(67 percent for single vehicle 

rollovers and 42 percent for 

multi-vehicle.) This also holds 

true regardless of the number 

of quarter turns. The noncontact force is associated with 

17 percent of single vehicle 

rollovers including fall-over, which 

occurs in 13 percent of single 

vehicle rollover crashes. Noncontact forces describe a roll 

precipitated by centrifugal or 

gravitational forces. At three or 

more quarter turns, roughly 57 

percent of tripping is attributable 

to wheel/tire engagements. 

Wheel rim contact is associated 

with tripped rollover while the tire 

force only is related to untripped 

rollover.

Although 42 percent of the 

multi-vehicle rollover crashes 

are initially tripped at the 

wheels/tires, 35 percent are 

attributable to the side plane. 

Further, the side-plane incidents 

are concentrated at one quarter 

turn (45 percent) indicating a 

potentially lower severity crash. 

The side plane refers to any side 

plane other than the wheels and 

tires that precipitates rollover.

Behavioral Elements

In reconstructing rollover crashes, 

it is important to understand the 

behavioral elements attributable 

to the event. Examination of the 

pre-event movement prior to 

the recognition of critical event 

and quarter turn frequency, 

with regard to driver inputs, as 

described in CDS, are included.

In single vehicle, non-planar 

events approximately 49 percent 

of the drivers sought to negotiate 

a turn. Forty-one percent seem 

to have failed to continue on their 

straight path. The remaining 

pre-event movements were 

seen to occur very infrequently 

and included: an absence of 

driver, decelerating in traffi c 

lane, accelerating in traffi c lane, 

starting in traffi c lane, stopped in 

traffi c lane, passing or overtaking 

another vehicle, disabled or 

parked in travel lane, leaving 

a parking position, entering a 

parking position, turning right, 

turning left, making a U-turn, 

backing up (other than for 

parking position,) changing lanes, 

merging, successful avoidance 

maneuver to a previous critical 

event, other movement, or 

unknown.

In multi-vehicle, non-planar events, 

60 percent of the drivers failed 

to continue in a straight path. 

Sixteen percent were attempting 

a left turn movement prior to the 

rollover event. These were noted 

as the highest frequency multivehicle pre-event movements.

Occupant Demography

Owing to the small sample size 

of occupants involved in rollover 

crashes, the crash confi gurations 

were collapsed into one data 

set. The attributes of interest 

were on-scene disposition of the 

occupant, restraint use, ejection, 

and injury severity.

On-Scene Occupant Disposition

The severity of rollover crashes 

is suggested by the following 

comparisons. Fifty-six percent of 

occupants receive some form 

of treatment, as compared to 

40 percent of planar crash 

occupants. Further, for rollovers 

with more than two quarter 

turns, the number of occupants 

receiving no treatment 

experiences a sharp decline from 

24 to 11 percent.

Occupant Restraint Use

The data supports the advocacy 

for manual restraint use. 

Although the Occupant Protection 

Standard (FMVSS 208) does 

not require a safety belt test 

under rollover conditions, the 

safety belt does provide the 

intended result of retaining most 

restrained occupants within the 

vehicle. By virtue of restraint 

use, these occupants generally 

walk away from the rollover 

sequence. Additionally, these 

occupants experience crashes of 

higher severity with regard to the 

recorded quarter turns and are 

not ejected. It is found that most 

of the occupants classifi ed at 

the various treatment levels are 

restrained.

It has long been theorized that 

risk takers generally succumb 

to rollover. This may be at least 

partially supported by elevated 

incidence of unrestrained occ-
National Center for Statistics and Analysis 400 Seventh St., S.W., Washington, D.C. 20590

upants in rollover crashes. Among 

planar crash occupants, 27 

percent failed to use a safety belt 

(were unrestrained), as compared 

to 35 percent of the rollover 

(other than zero quarter turn) 

crash occupants, per Table 3.

Ejection

As noted previously, those who 

were belted fared better than 

those unrestrained occupants. 

Further, ejection incidence was 

found to be far lower among those 

restrained. Although testing has 

not subjected restraint systems 

to the forces imparted during a 

rollover crash, they have been 

shown to retard the outward 

motion of the occupants.

As seen in Table 4, those 

unrestrained occupants who 

remained within the vehicle 

(30 percent of the rollover 

population) will have benefi ted 

from the integrity of the 

occupant compartment but will 

have sacrifi ced potential injury 

mitigation afforded by restraint 

use. The data suggested that 

the restrained occupants were 

able to withstand rollover without 

being ejected at a greater 

frequency than those who were 

unrestrained. Of the partially and 

completely ejected occupants, 

81 percent were unrestrained, 

as compared to the 18 percent 

who were protected by a safety 

belt. Among completely ejected 

occupants subjected to rollover, 

97 percent were unrestrained. In 

support of restraint use were the 

69 percent of all CDS-reported 

rollover occupants who by virtue 

of their restraint use were 

retained within the vehicle. The 

percentage of occupant retention 

during rollover was exceedingly 

high for a technology not directly 

addressing this situation.

Maximum Injury Severity

The Maximum Abbreviated 

Injury Scale (MAIS) describes 

the highest abbreviated injury 

severity score (AIS); based on 

mortality risk, sustained by an 

occupant. The scale ranges from 

minor (AIS 1) through maximum 

(AIS 6) injuries and unknown (AIS 

7.) Ten percent of all occupants 

injured in rollover were seriously, 

including fatally, injured, as shown 

in Table 5. Another 15 percent 

of occupants sustained MAIS 

injury in the moderate range. 

Since most rollover crashes 

resulted in two quarter turns 

or less, thereby safeguarding 

the integrity of the vehicle, it 

was not surprising that rollover 

injuries were predominantly of 

lower injury severity. This did 

not mean that rollovers were 

benign in nature. Most planar 

crashes were also of low injury 

severity, per Table 6. In rollover 

Table 3

Percentage of Occupants Involved in Crashes by Restraint Use and Number 

of Quarter Turns (Totals given in thousands, weighted. Sample sizes given in 

parentheses.)

 

 Quarter Turns 

 (Column Percentage) EndSafety over- Unk (in ‘000’s)

Belt Use 0 1 2 3+ End Num Total

 

No 27% 35% 34% 34% 67% 51% 7,277

 (n=17,465) (n=544) (n=888) (n=1,783) (n=71) (n=232) 28%

Yes 71% 64% 65% 66% 32% 48% 18,340

 (n=28,564) (n=684) (n=959) (n=1705) (n=38) (n=187) 70%

Unknown 2% 1% 1% 1% 2% 1% 459

 (n=1,053) (n=22) (n=50) (n=45) (n=5) (n=16) 2%

Total 23,480 447 1053 983 16 102 26,080

 (n=47,082) (n=1,250) (n=1,897) (n=3,533) (n=114) (n=435) 100%

Note: Slight differences may exist in percentage calculations owing to rounding.

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

Table 4

Percentage and Number of Occupants Involved in Rollover Crashes by 

Ejection Status and Restraint Use (Total column given in thousands, weighted)

 Restraint Use

Ejection (Row Percentage) (in ‘000’s)

Status No Yes Unk. Total 

No Ejection 30 % 69 % 1 % 2,355

 92%

Complete Ejection 97 % 3 % 0 % 142

 6%

Partial Ejection 49 % 51 % 0 % 69

 3%

Ejection - 87 % 12 % 1 % 2

Unknown Degree 0%

Total 34 % 65 % 1 % 2,567

 100%

Note: Slight differences may exist in percentage calculations owing to rounding.

Source: NCSA, NHTSA, NASS-CDS, 1995-2001
National Center for Statistics and Analysis 400 Seventh St., S.W., Washington, D.C. 20590

crashes, however, 49 percent 

of occupants experiencing three 

or more quarter turns sustained 

minor injuries. When examining 

the percentage of occupants 

involved in rollover crashes, 

injury patterns indicated the 

potential detriment to the 

occupant involved in a rollover 

versus a planar crash. As a 

percentage, MAIS scores for 

rollover occupants tended to be 

greater than those for planar 

crash occupants.

Table 5

Percentage of Injured Occupants, 

by Injury Severity and Crash 

Attitude

Injury Severity Crash Attitude

(MAIS) Planar Rollover

Minor 86 % 74 %

Moderate 9 % 15 %

Serious - Maximum 5 % 10 %

All Known Injured 100 % 100 %

Note: Slight differences may exist in percentage 

calculation owing to rounding.

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

Among CDS crashes, 70 percent 

of occupants were restrained, 

as compared to 28 percent 

who were unrestrained, per 

Table 3. Upon disaggregation, 

however, 64 percent of rollover 

occupants were restrained and 

35 percent were unrestrained. 

Although a very high incidence 

of crashes resulted in low MAIS 

scores, this may have been a 

masking effect of the restrained 

in relation to the unrestrained 

occupant outcomes. Among 

rollover crashes, as compared to 

planar crashes, a slightly lower 

percentage of MAIS 1 injuries 

existed. As a percentage, MAIS 

readings for rollover occupants 

tended to be greater than those 

for planar crash occupants.

Injuries by Body Region

Thirty-three percent of all 

reported injuries occurring in 

non-planar crashes affected the 

head. Another one percent were 

assessed as neck injuries. Rains 

and Kanianthra (SAE 1995) 

suggested, that headroom 

reduction increased head injury 

risk, however, they did not 

discount the risks associated 

with vertical occupant excursion. 

It may be reasoned that the neck 

may fi rst have loaded the roof, and 

rebounded off the roof thereby 

creating a two-pronged insult. 

Neck injuries of lower severity 

may have been overlooked or may 

not have manifested themselves 

until after examination. Similarly, 

non-life threatening neck injuries 

may have been overlooked in 

severely injured occupants. 

These considerations may be 

attributable, at least in part, 

to the necessity to immediately 

treat more severe, potentially 

life-threatening injuries in the 

emergency room. The initial 

examinations may allow less 

severe injuries to remain 

unidentifi ed until further 

examination or never become 

documented for CDS.

Restrained occupants sustain 

nearly half of the injuries to 

extremities, as seen in Table 7. 

The compression of the occupant 

compartment and fl ailing of 

members may partially explain 

the head/face and extremity 

injury frequency that is evident for 

the unrestrained occupants. For 

restrained occupants, the thorax 

most frequently sustains serious 

injury. In contrast, the head and 

face of unrestrained occupants 

are the most vulnerable to 

serious injury. On average for 

these rollover data, three injuries 

are recorded for unrestrained 

and six for restrained occupants. 

Of injuries to unrestrained 

occupants, 23 percent are 

at least of AIS 2 severity, as 

compared to 10 percent for the 

restrained occupants.

Table 6

Percentage and Number of Rollover Occupants, by Maximum Injury 

Severity and Number of Quarter Turns

 Quarter Turns

 (Column Percentage) End-

 over- Unknown (in ‘000’s)

 MAIS 0 1 2 3+ End Number Total

 0 51 % 39 % 53 % 26 % 2 % 12 % 12,840

 No Inj. 50 %

 1 39 % 47 % 34 % 49 % 54 % 38 % 10,060

 Minor 39 %

 2 4 % 7 % 6 % 11 % 8 % 17 % 1,206

 Moderate 5 %

 3 – 6 2 % 4 % 3 % 9 % 32 % 10 % 669

 Serious – Max. 3 %

 7 4 % 3 % 4 % 5 % 5 % 23 % 1,088

 Unknown/Severe 4 %

 Total 23,290 438 1,041 979 16 100 25,860

 100 % 100 % 100 % 100 % 100 % 100 % 

Note: Slight differences may exist in percentage calculation owing to rounding.

Source: NCSA, NHTSA, NASS-CDS, 1995-2001
National Center for Statistics and Analysis 400 Seventh St., S.W., Washington, D.C. 20590

Conclusions

In this review of NASS – CDS data 

over the years 1995 through 

2001, rollover crash mechanisms 

and their related injury patterns 

are summarized. Although the 

single vehicle rollover is a highly 

complex crash mode, the multivehicle rollover becomes less 

clear with the added dimension 

of a planar component. For this 

reason, only single vehicle crash 

mechanisms are considered in the 

summation. Owing to the small 

sample size, however, injuries of 

single and multiple vehicle crash 

confi gurations are aggregated 

within the study and for the 

summarization that follows. 

Based on the data examined in 

this report, it possible to address 

the questions posed in the Section 

“Objectives” regarding: prevalent 

rollover crash attributes and 

injury outcomes for occupants of 

rollover crashes.

Which are the Prevalent Rollover 

Crash Attributes?

The tripping mechanism generally 

inducing rollover was the ground 

with initial tripping force exerted 

at the wheels/tires. The tripover type of rollover was found 

to be the most prevalent. Most 

rollovers ended in one or two 

quarter turns. Slightly more than 

half of the single vehicle crashes 

rolled to the left, driver side 

Table 7

Percentage of Injuries Sustained by Occupants Involved in Rollover Crashes 

by Injured Body Region, Restraint Use, and Injury Severity

 Safety Injury Severity

 Belt (Row Percentage) (in ‘000) 

Injured Body Region Use AIS 1 AIS 2 AIS 3-6 AIS 7 Total

Head/Face No 76% 13% 11% 1% 981

 Yes 89% 7% 3% 0% 882

 All 82% 10% 7% 0% 1,872

Upper & Lower No 82% 13% 5% 0% 1,017

Extremities Yes 93% 6% 2% 0% 1,372

 All 88% 9% 3% 0% 2,398

Spine No 71% 23% 6% 0% 283

 Yes 91% 7% 2% 0% 342

 All 82% 14% 4% 0% 628

Thorax No 66% 6% 27% 1% 221

 Yes 77% 7% 14% 1% 233

 All 71% 7% 21% 1% 455

Abdomen No 67% 20% 11% 1% 130

 Yes 74% 18% 7% 1% 95

 All 70% 19% 9% 1% 227

Unspecifi ed No 99% 0% 1% 0% 57

 Yes 98% 0% 2% 0% 37

 All 99% 0% 1% 0% 94

Neck No 91% 3% 3% 3% 23

 Yes 99% 1% 0% 1% 37

 All 96% 2% 1% 1% 60

Total No 77% 14% 9% 0% 2,712

 Yes 90% 7% 3% 0% 2,998

 All 84% 10% 6% 0% 5,734

Note: Slight differences may exist in percentage calculation owing to rounding.

The “All” category includes the unknown restraint category, however, it is not explicitly included in the table.

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

leading. As the counterpoint, 

it was noted that the turn-over 

(untripped) rollover type was the 

least frequent type of rollover 

crash.

What is the Injury Outcome for the 

Rollover Occupants?

The occupant data were sorted 

in relation to restraint use and 

crash confi guration. It was 

noted that among rollover crash 

occupants, the percentage that 

were unrestrained was higher 

than the analogous percentage 

among planar crashes. Also, 

unrestrained occupants were at 

the greatest risk for injury and 

ejection. Further, MAIS readings 

for rollover occupants were 

proportionally higher than those 

for planar crash occupants. 

The head and extremities were 

injured with greatest frequency. 

It can be concluded that there 

would have been a larger number 

of severe injuries were it not for 

the benefi ts of safety belt use.

The research is on-going and 

subsequent phases will be 

published in the form of research 

notes and technical reports. The 

next phase will contemplate the 

issues discussed below.

Issues Identifi ed with Current 

Parameters and Rationale for 

Future Modifi cations

In examining the data for all 

occupants and their vehicles, 

issues were encountered. These 

issues existed in comparing the 

injury outcomes and vehicle 

damage and included: crash 

confi guration, impact orientation, 

occupant biomechanics, seating 

position, and clinical case 

analysis.

Crash Confi guration

The crash confi guration should 

be considered in this type of 
National Center for Statistics and Analysis 400 Seventh St., S.W., Washington, D.C. 20590

analysis. The bulk of the rollovers 

are attributable to single vehicle 

events. However, the presence 

of other vehicles introduces 

issues beyond those within the 

traditional single vehicle rollover. 

It may also be useful to determine 

whether the case vehicle that 

does roll acts as the bullet or 

struck vehicle.

Impact Orientation

Additionally, the issue of near 

side versus far side leading 

rollovers must be considered in 

tandem with the quarter turn 

progression. Consideration to 

the occupant position and his 

relation to the leading side may 

be useful. First, for purposes of 

comparison, planar crashes of 

near side and far side may be 

used. Further, the occupant on 

the far side of the roll initiation 

generally sustains the most 

severe injuries.

Occupant - Biomechanics

Crash injury outcomes should be 

reported separately for children 

and adults. The biomechanical 

responses of children are 

different from those of adults. 

First, vehicle hardware is 

designed for adults. Secondly, 

child safety seats are retrofi t 

items that are meant to work 

in concert with a wide variety of 

restraint hardware found in the 

vehicle fl eet. Finally, children lack 

soft tissue and bone development. 

They will not be fully developed, in 

general, until the child reaches 

12 years of age.

Occupant – Seating Confi guration

Crash severities for front and 

rear seated occupants are 

different. Further, crash severity 

estimates can be biased by 

presence of vehicles with many 

occupants. The representation 

of the vehicle fl eet suggests that 

there are many seating positions 

other than the front that might be 

occupied, however, consideration 

for mass, human and cargo, 

distribution should be considered. 

For normalization of the data 

analysis, it is suggested that the 

driver and right front passenger 

would serve to balance impact 

orientation reporting.

Clinical Case Analysis

Finally, based upon this update, 

CDS variables and attributes 

should be revised to capture 

more specifi c elements of rollover 

crashes. Of specifi c interest is the 

further defi nition of the rollover 

object to which an attribute 

might be ascribed. For instance, 

the width of a curb or the type 

of ground could be aggregated 

in a statistical analysis, however, 

for an engineering analysis the 

disaggregated elements may be 

crucial. These descriptors could 

lead to better understanding of 

the true sequence of a rollover 

crash and eventual test design 

based upon these concepts. 

Some of these descriptors 

might be found via clinical 

review for cases with copious 

supplementary information. 

Currently, however, the existing 

CDS variable set does not require 

this type of reporting.

References

! Federal Highway Administration, 

“Vehicle Test Summary for Roof 

Crush Drop Test (Chevrolet S-10) 

on Load Cell Plate (3x4), 03005 

A&B”, Washington, D.C., 2003.

! Henderson, Michael, Paine, 

Michael, “Passenger Car Roof 

Crush Strength Requirements”, 

Department of Transport and 

Regional Development, The 

Federal Offi ce of Road Safety 

(Australia), Canberra, 1998.

! Hendriks, D., Scheiffl ee, T., 

Page, J., Bellis, E., “Analysis of 

Untripped Rollovers, Final Report 

Technical Findings”, CALSPAN, 

Buffalo, 1998.

! Hertz, Ellen, “Passenger Vehicles 

in Untripped Rollovers”, NHTSA, 

Washington, D.C., 1999.

! National Archives and Records 

Administration, Code of Federal 

Regulations, 49 Parts 400 to 

999, 

! Revised as of October 1, 2001, 

Transportation, Washington, 

D.C., 2001.

! Rains, Glen C. and Kanianthra, 

Joseph N., “Determination of 

the Signifi cance of Roof Crush 

on Head and Neck Injury to 

Passenger Vehicle Occupants in 

Rollover Crashes”, SAE, 1995.

! United States Department of 

Transportation, National Highway 

Traffi c Safety Administration, 

“National Automotive Sampling 

System, Crashworthiness Data 

System, 2000 Coding and Editing 

Manual”, NHTSA, Washington, 

D.C., 2000.

For additional copies of this research note, please call 

1 800 934 8517 or fax your request to 202 366 3189. 

For questions regarding the data reported in this research, 

contact Ana María Eigen [202 366 2903]. This research note 

and other general information on highway traffi c safety may be 

accessed by internet users at: http://www-nrd.nhtsa.dot.gov/

departments/nrd-30/ncsa/AvailInf.html