Paper No.: 12-3645
The Effect of Driver Height on the Death Rate in Single-Vehicle Rollover
Accidents
Jonathan E. Howson
Senior Research Associate
Zachry Department of Civil Engineering
Texas A&M University
College Station, TX 77843-3135
Email: [email protected], Tel: 903-802-8757, Fax: 979-845-0278
Dominique Lord*
Associate Professor and Zachry Development Professor I
Zachry Department of Civil Engineering
Texas A&M University
3136 TAMU
College Station, TX 77843-3136
Email: [email protected], Tel: 979-458-3949, Fax: 979-845-6481
D. Lance Bullard
Division Head
Research Engineer
Roadside Safety and Physical Security Division
Texas Transportation Institute
The Texas A&M University System
3135 TAMU
College Station, TX 77843-3135
E-mail: [email protected], Tel: 979-845-6153, Fax: 979-845-6107
Transportation Research Board
91st Annual Meeting
January 22-26, 2012
Washington, D.C.
November 14, 2011
Number of words= (4532 Words + 11 Tables + 1 Figure) = 7,582
*Corresponding author
ABSTRACT
The average American male age 16 and over is 5-ft, 9-in. (69 inches) tall and the average
American female age 16 and over is 5-ft. 4-in. (64 inches). Utilizing data from the National
Center for Health Statistics, it was found that only 19.7% of males are 72-in or taller and only
0.15% females reach or exceed 72-in. The statistics on height distribution were compared with
the information obtained from the Fatal Accident Reporting System Encyclopedia (FARS) on the
number of deaths from single-vehicle rollover accidents as correlated to occupant height. Since
individuals 72-in or taller have less headroom (defined as the vertical space between the interior
of the roof and the bottom of the seat) in vehicles than the average individual, they therefore
have a greater probability of having head injuries when the vehicle rolls over. The average head
clearance for the average American male and female is 3.67-in and 4.38-in, respectively; with
the head clearance for a 72-in male and female being 2.57-in and 3.60-in, respectively. The
results of this study show that male (t-value=4.72, p<0.001) and female (t-value=1.41, p=0.16)
drivers 72-in or taller are more likely to be killed in rollover accidents as based on their
population percentage; the results for female drivers are less conclusive due to the small sample
size. In addition, vehicles were divided into different categories and examined to see if vehicles
for certain categories had increased fatalities for male drivers 72-in or taller. It was found that
seven of the thirteen vehicle categories showed a higher than average fatality rate for 72-in or
taller drivers (all t=values≥1.96, p≤0.05).
1
INTRODUCTION
In 1971, the Federal Motor Vehicle Safety Standard (FMVSS) 216 was implemented to provide
a minimum roof strength for passenger cars. The purpose of this standard was to reduce deaths
and injuries due to the crushing of the roof into the passenger compartment in rollover accidents.
The resistance of the roof to intrusion is determined by a quasi-static test, in which a force of 1.5
times the empty weight of the vehicle or 5,000 pounds, whichever is less, is gradually applied to
the roof in the vicinity of the “A” pillar. The force is applied by a flat test device at a 25° roll
angle (sideways) and a 5° pitch angle (forward) to simulate the direction of forces that can be
encountered in a rollover. During the test, the roof may show no more than 5 inches of intrusion,
as measured by the movement of the test device.
In April 1991, FMVSS 216 was updated to include light trucks and vans with an empty
weight of 6,000 pounds or less. To accommodate the heavier vehicle weights, the 5,000 poundlimit increased to 6,000 pounds; meaning the vehicle roof has to support 1.5 times the empty
vehicle weight or 6,000 lbs (1).
The National Highway Traffic Safety Administration (NHTSA) recently updated FMVSS
216 to include vehicles up to 10,000 pounds (FMVSS 216a). It also requires that a roof
withstand an applied force equal to 3.0 times the vehicle’s weight while maintaining sufficient
headroom for an average size adult male. The new standard will be phased in over the coming
years, with all vehicles manufactured after September 1, 2015 being required to meet this
standard (2).
Rollover crashes are actually a low severity type of accident because the impact energy is
dissipated over seconds, rather than milliseconds as in a fontal collision (3). Friedman and Nash
(4) discovered that the speed at which a vehicle’s roof impacts the ground during a rollover event
is 5 mph or less. If no roof intrusion occurs, the occupant’s head meets the padded roof at this
velocity and at low enough forces not to cause serious neck or head injury (4). Studies by
Nusholtz et al. (5) and Yoganandan et al. (6) used complete unembalmed cadavers to test the
effect of drop height on the formation of cervical spine damage due to impacts to the top of the
head. Their main findings relating to this research is that a reasonably healthy person would be
able to survive a fall of one meter (3.28 feet) on his or her head if they landed on a reasonably
padded surface. A one-meter fall resulted in an impact velocity of 4.5 meters/sec (10.23 mph).
Friedman and Nash (4) discovered that when roof intrusion occurred, it took place at the
rotational speed of the vehicle, which can be much greater than the roof impact speed. From
experiments, the researchers determined that the velocity of an intruding roof had an
amplification factor of 3 as compared to the roof impact speed. According to Nusholtz et al. (5)
and Yoganandan et al. (6), this increase in impact speed is significant enough to cause vertebra
damage or death.
The risk of injury from this type of crash is not due to the crash itself, but a lack of
occupant protection provided by the vehicle (3). The FMVSS 216 static test used by vehicle
manufacturers to design the roof of vehicles applies substantially less force then is seen in an
actual dynamic rollover event. Also, this test applies the load in such a way as to allow the
windshield to supply 30% of the roof’s static strength (4). Friedman and Nash went on to say
that in a dynamic rollover event the windshield is fractured or shattered during the first roof
contact event and will not provide any support on subsequent roof contact events, making the
roof more likely to intrude into the occupant’s survival space (4).
Therefore, one of the main reasons rollover crashes are so dangerous is because of roof
intrusion and roof contact injuries. To protect occupants in a rollover, maintaining headroom is
2
very important. Headroom is defined as the vertical distance between the interior of the roof and
the seat bottom. A study by Partyka (7) showed that vehicles in eighty percent of rollover
crashes, with two or more vehicle quarter turn rolls, sustained vertical roof intrusion (which
included the roof top, roof side rails and front/rear headers). The roof is part of the structural
support of a vehicle and is therefore a critical component in keeping the occupant safe. If a roof
crushes substantially during an accident, from a failure of the side rails, headers, or support
pillars, catastrophic injuries can occur. Often, this decreased headroom results in the occupant’s
head impacting some portion of the vehicle causing death, paralysis, or brain damage. A study
by NHTSA found that head injury increased when headroom was reduced after a rollover event;
with the risk of head injury from roof contact substantially increased when headroom (preversus post-crash) was decreased by more than 70% (8).
To date, research has not been performed to examine the influence of driver’s height on
the risk of death when a rollover occurs using observed data collected in the field. Most of the
previous work has been conducted in a controlled environment and was usually associated with
the development of standards. Therefore, the objective of this paper is to examine the effect of
driver height on the death rate of single-vehicle rollover crashes. The study objective was
accomplished using data collected from the National Center for Health Statistics, NHTSA’s Fatal
Accident Reporting System (FARS) for the time period 1999-2009, and a database containing
headroom vertical distance for several vehicle body types and vehicle makes. Risk values were
estimated for men, women and different categories of vehicles.
DATA DESCRIPTION
Height Distribution
FMVSS 216 is designed to protect a population of height up to approximately the average size
adult male. As mentioned earlier, the average male adult is 69-in tall (9). However, all adult
males are not 69-in tall. The height distribution of a random sampling of adult males and/or
females should follow a normal distribution. McDowell et al. (9) from the National Center for
Health Statistics published their height distribution data as percentiles, as seen in Table 1. This
data were used in calculate the percentage of males and females that are 72-in or taller.
TABLE 1 Height Distribution of Males and Females in Percentiles (9)
Men
Percentile
Height
5
64.4
10
65.6
15
66.3
25
67.4
50
69.4
75
71.5
85
72.6
90
73.2
95
74.3
50
63.8
75
65.6
85
66.5
90
67.2
95
68.2
Women
Percentile
Height
5
59.3
10
60.3
15
61
25
62.1
Sitting Height
Bardeen (10) conducted a study to determine the relation between stature (standing height) and
sitting height. His findings are summarized in Tables 2 and 3 for males and females,
respectively (10). Bardeen (10) found that a 69-in tall adult male has a sitting height of 35.91-in
and a 64-in adult female has a sitting height of 33.82-in. It is also noted that the difference
3
between the sitting heights of an average adult male and a male of 72-in. is 1.1 inches. This
difference increases to over 2-in when the individual is 75-in or taller. Bardeen (10) found that
females have a lower sitting height as compared to a male of the same height. A female of 72-in
has roughly the same sitting height as a 69-in male.
TABLE 2 Stature and Sitting Heights of Adult Male Americans (10)
Stature
Inches
cm.
Number of
Individuals
57
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
144.80
149.90
152.40
154.90
157.50
160.00
162.60
165.10
167.64
170.18
172.72
175.26
177.80
180.34
182.88
185.42
187.96
190.50
193.04
1
1
1
2
2
10
21
29
52
48
67
70
48
34
21
13
2
2
1
Mean Sitting Height
Inches
cm.
31.50
32.01
33.50
32.99
33.50
33.11
33.78
34.06
34.61
34.88
35.31
35.91
36.42
36.50
37.01
36.89
37.28
37.91
37.99
80.00
81.30
85.10
83.80
85.10
84.10
85.80
86.50
87.90
88.60
89.70
91.20
92.50
92.70
94.00
93.70
94.70
96.30
96.50
4
TABLE 3 Stature and Sitting Heights of Adult Female Americans (10)
Stature
Inches
55.5
58.0
59.0
60.0
61.0
62.0
63.0
64.0
65.0
66.0
67.0
68.0
69.0
71.0
72.0
cm.
141.00
147.30
149.90
152.40
154.90
157.50
160.00
162.60
165.10
167.60
170.20
172.70
175.30
180.30
182.90
Number of
Individuals
1
2
8
23
31
55
65
58
46
42
20
6
7
1
1
Mean Sitting Height
Inches
27.28
30.98
31.81
32.20
32.91
32.91
33.46
33.82
34.09
34.69
34.88
35.31
35.20
35.98
35.98
cm.
69.30
78.70
80.80
81.80
83.60
83.60
85.00
85.90
86.60
88.10
88.60
89.70
89.40
91.40
91.40
Vehicle Headroom
Vehicle headroom is defined as the vertical distance from the seat to the bottom of the roof liner.
The amount of vehicle headroom afforded varies from vehicle to vehicle, but in general, pickup
trucks and SUVs offer more headroom than passenger and sports cars. On the other hand,
pickups and SUVs are more likely to be involved in a rollover accident due to their higher center
of gravity.
The FARS database places every vehicle into one of 15 different vehicle body type
categories. By looking at categories of vehicles instead of all vehicles together, vehicles that are
more dangerous to people of above average height can be identified. An important note is that
soft-top convertibles are not regulated by the FMVSS 216 standard.
The next step is to determine the average headroom for each category. The first step
taken to accomplish this was to determine the top selling vehicles in the US for 2009. The
statistics for 2009 are used because FARS only had data published to 2009 (at the time the study
was completed). This list will represent the vehicles with the highest volume on the roadways
and will be used to determine the headroom for the different vehicle categories. The top 20 list
is shown in Table 4 below (11).
5
TABLE 4 Top 20 Best Selling Vehicles: 2009 (11)
Total Yearly Sales
Top 20 Best Selling Vehicles:
2009
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Ford F-Series P/U
Toyota Camry
Chevrolet Silverado P/U
Toyota Corolla
Honda Accord
Honda Civic
Nissan Altima
Honda CR-V
Ford Fusion
Dodge Ram P/U
Ford Escape
Chevrolet Impala
Chevrolet Malibu
Ford Focus
Toyota RAV4
Toyota Prius
Hyundai Sonata
GMC Sierra P/U
Chevrolet Cobalt
Hyundai Elantra
413,625
356,824
316,544
296,874
290,056
259,722
203,568
191,214
180,671
177,268
173,044
165,565
161,568
160,433
149,088
139,682
120,028
111,842
104,724
103,269
Using the vehicle categories listed in FARS with the list of vehicles shown in Table 4, a
composite list can be formed with example vehicles in each category and their corresponding
headroom (using the “Specs & Features -> Interior” tabs at http://home.autos.msn.com/) (12).
Table 5 presents an example of a vehicle used in each category. The full list of vehicles in Table
5 is still not complete, as it leaves out many makes and models of vehicles; however, it does
contain many of the most popular, and therefore abundant vehicles on the roadways. There were
two main considerations which went into choosing the vehicles for the categories described in
Table 5. The first was the popularity of the vehicle and the second was choosing vehicle models
that existed both in 2009 and 1999 so as to capture the change in headroom of vehicles over
time. The last four columns of Table 5 contain the clearance between the driver’s head and the
bottom of the roof liner for a 69-in adult male and a 72-in adult male, respectively. It can be
seen in Table 5 that the clearance between the driver’s head and the bottom of the roof liner is
less than 5-in for every vehicle category except truck tractor for individuals 72-in or taller.
Vehicle designs allow the roof to intrude 5-in into the passenger cabin during a rollover event, as
per FMVSS 216.
FARS Encyclopedia
The data needed to complete this work was obtained from FARS. Relevant information from
years 1999 – 2009 was queried to obtain the relevant information needed for this work.
Information prior to 1999 did not include information regarding driver height and was therefore
not applicable. Table 6 shows the data fields selected to extract the relevant information from
FARS.
6
TABLE 5 Head Clearance by Vehicle Category (12)
2009 Statistics
1999 Statistics
Total
Averge for Type Headroom Averge for Type Average
Type
Example
Convertible
Ford Mustang
38.8
38.80
38
37.83
2-Door Sedan
Honda Civic
37.8
39.13
38.8
3-Door Sedan
Ford Focus
39.1
38.45
4-Door Sedan
Toyota Camry
38.8
5-Door Sedan
Volkswagen Golf
Station Wagon
Head Clearance
69" Adult
Male
72'' Adult
Male
38.31
2.40
1.30
38.23
38.68
2.77
1.67
39.3
39.05
38.75
2.84
1.74
39.36
38.6
39.32
39.34
3.43
2.33
38.6
39.57
38.6
39.43
39.50
3.59
2.49
Subaru Outback
40.8
39.27
39.3
39.20
39.23
3.32
2.22
Compact Utility
Honda CR-V
40.9
40.70
40.5
40.40
40.55
4.64
3.54
Large Utility
Chevy Tahoe
41.1
39.98
40.7
39.90
39.94
4.03
2.93
Utility Station wagon
Chevy Suburban
41.1
40.00
40.7
39.80
39.90
3.99
2.89
Minivan
Chrysler Town and
Country
39.8
41.10
39.8
40.33
40.71
4.80
3.70
Large Van
Chevy Express
40.2
41.10
40.6
41.55
41.33
5.42
4.32
Compact Pickup
Toyota Tacoma
40
39.63
38.7
39.20
39.41
3.50
2.40
Standard Pickup
Ford F150
41
40.75
40.8
40.58
40.66
4.75
3.65
Truck Tractor
Freightliner Coronado
~ 70
70.00
~ 70
70.00
70.00
34.09
32.99
Headroom
7
TABLE 6 Data Field Selected in FARS
Category
Vehicles
Persons
Drivers
Relevant Information
Specific Information
Body Type
Most Harmful Event
Rollover
Injury Severity
Restraint System Used
Seating Position
Sex
Driver Height (Feet)
Driver Height (Inches)
All
Rollover
1st Event
Fatal
Lap & Shoulder
Front Left - Driver
All
All
All
The selection criteria are as follows:
• Body Type – Determine if any vehicles are more dangerous to individuals over 72-in.
• Most Harmful Event – The rollover event should be the most harmful event.
• Rollover – The rollover was chosen as the first event to ensure no other factors lead to the
driver’s death; such as an impact with another vehicle prior to the vehicle rolling over.
• Injury Severity – Examine whether driver height has any influence on death rate in
rollover accidents. Therefore, only fatalities are considered.
• Restraint System Used – Only consider drivers properly belted into the vehicle. Unbelted
drivers are much more likely to be killed regardless of height.
• Seating Position – FARS only records height of drivers; therefore, only the driver is
considered. This eliminates children and causes the search to look at people 15+ years
old. However, it reduces the number of results in the search and causes the results to
omit the affect of other occupant seating positions.
• Sex – Separate male and female fatalities since each gender has a separate height
distribution curve.
• Driver Height (Feet) – Used to separate total fatalities into one-foot height increments.
This is used to determine percent fatalities over 6-ft.
• Driver Height (Inches) – Further breaks down total fatalities into increments of one inch.
RESULTS
Height Distribution
To determine the percentage of males and females taller than 72-in it is necessary to convert the
percentile data (Table 1) to a standard normal distribution. The standard normal distribution has
a mean value of zero and a standard deviation of 1. The equation needed to convert a normal
distribution to a standard normal distribution is:
(1)
where, Z is the standard normal random variable, X is normal random variable, μ is the average
of the normal distribution, and σ is the standard deviation of the normal distribution. When
converting from percentiles, the standard deviation is not known, but the Z value is equal to 95%
8
or -1.645 and X is equal to the value corresponding to the 5th or 95th percentile. Solving for the
standard deviation yields:
(2)
Once the standard deviation is known, it is possible to use Equation (1) to solve for the Z value
corresponding to a height of 72-in. Table 7 displays the results from these calculations.
Table 7 Percentage of Males and Females 72-in or Taller
Group
Sigma
Z
Percentage
Male
7.72
-0.85
19.71% (1.93%)†
Female
6.99
-2.96
0.15% (0.20%)
†
Standard error
Crash Data
The results from FARS, with the inputs given in Table 6, are summarized in Tables 8 and 9.
These tables show the total number of deceased males and females, the number over 72-in, the
percent total, and average and standard deviation, respectively.
Year
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
Table 8 Percent of Males Over 72-in Killed in Rollover Accidents
Males
Total
Over 72-in
Standard
% Total
Average
Deceased
Deceased
Deviation
697
204
29.27
317
99
31.23
369
103
27.91
378
114
30.16
382
117
30.63
348
100
28.74
30.71
2.47
331
117
35.35
339
98
28.91
270
81
30.00
300
106
35.33
241
73
30.29
9
Year
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
Table 9 Percent of Females Over 72-in Killed in Rollover Accidents
Females
Total
Over 72-in
Standard
% Total
Average
Deceased
Deceased
Deviation
282
2
1.39
144
1
0.69
159
1
0.63
213
2
0.94
171
3
1.75
176
1
0.57
0.83
0.67
199
1
0.50
173
1
0.58
138
0
0.00
136
0
0.00
142
3
2.11
It is clear that the average death rate for males and females in Table 8 and 9, respectively,
is greater than their respective populate percentage, as shown in Table 7. The next step is to
determine whether or not the values in Tables 8 and 9 are statistically significant at a 95%
confidence interval. Since the actual standard deviation is not known, the confidence interval
used is:
3
√
where, X is the sample mean (average percentage killed in rollover accidents),
, / is the
value from the t-distribution with probability α and n-1 degrees of freedom, s is the standard
deviation of the random sample, and n is the sample size. In this research, the sample size is 11
and the corresponding t-value is 2.228. Applying Equation 3 to the values calculated in Tables 8
and 9, the following confidence intervals can be computed (Table 10). Table 10 displays the
proportion of death rates along with the 95% confidence intervals for male and female drivers,
respectively. By taking account the uncertainty associated with the height distribution, males (tvalue=4.72, p<0.001) and females (t-value=1.41, p<0.16) 72-in and taller are more likely to be
killed in a single-vehicle rollover collision as compared to their population percentage (shown in
Table 6). However, the results are less conclusive (i.e., marginally significant) for females due to
the small sample size.
, /
TABLE 10 Confidence Intervals for Male/Female Death Rates (Percent)
Sex
Lower Bound
Average
Upper Bound
Male
29.05
30.71
32.37
Female
0.38
0.83
1.28
Vehicle Category
Are some vehicles more dangerous to drivers over 72-in then others? To analyze this hypothesis,
the percent of people 72-in and taller killed in each vehicle category contained in FARS was
10
computed for each of the study years. Only data for males was used due to the limited number of
female fatalities and corresponding high degree of variability. The average was taken over the
years of interest as well as the standard deviation of the values. In addition, uncommon vehicle
categories with little or no data for each year were removed due to the variability of the results.
The final results are shown in Table 11 below.
TABLE 11 Percent Fatalities of Male Drivers 72-in and Taller by Vehicle Category
Body Type Years 2009 2008 2007 2006 2005 2004 2003 2002 2001 2000 1999 Average Standard Deviation < 6,000 lbs Convertible 22 50 0 0 25 0 50 25 0 67 67 27.78 26.73 2‐Door Sedan 38 35 15 35 25 18 33 33 39 36 44 32.02 8.84 3‐Door Sedan 6 29 36 27 33 57 29 20 0 50 25 28.38 16.67 4‐Door Sedan 28 31 28 33 30 28 31 18 27 24 20 27.21 4.78 Station Wagon 38 25 50 25 50 17 50 67 0 0 25 31.44 21.52 Compact Utility 31 31 31 19 28 30 38 31 31 30 28 29.69 4.38 ≥ 6,000 lbs Large Utility Utility Station Wagon Minivan 28 19 20 38 23 27 58 38 22 55 67 35.86 16.88 0 0 33 20 50 40 100 75 0 50 0 33.48 33.77 10 20 0 11 20 0 27 25 30 17 11 15.56 10.15 Large Van 14 33 0 80 33 75 0 17 0 20 0 24.78 28.94 Compact Pickup 21 31 41 25 25 23 30 26 17 35 29 27.55 6.72 Standard Pickup 35 35 19 44 35 28 39 34 36 37 39 34.54 6.37 Truck Tractor 34 36 38 32 40 33 36 26 48 46 48 37.92 6.82 Total 29 31 28 31 31 29 35 29 30 35 30 30.71 2.47 From Table 11, it is seen that the vehicle categories with the highest fatality percentage
are: large utility, utility station wagon, standard pickup, and truck-tractor. Conversely, it can
also be noted that these vehicle categories have some of the largest amount of headroom for the
drivers. However, recall that FMVSS 216 only applies to vehicles under 6,000 pounds, and
vehicles under 6,000 pounds have to support 1.5 times the empty vehicle weight or 6,000
pounds; whichever is less. Many of the vehicles under those vehicle categories exceed the 6,000
pound weight limit, and therefore do not have any regulation for roof strength. It should be
pointed out, however, that some manufacturers still elect to meet the standards to promote the
roof strength of their vehicles. Thus, it is possible that this attribute could influence the results
for this category of vehicles, but there is no way to know unless the company is contacted
directly. Most of the remaining vehicles have empty vehicle weights very close to 6,000 pounds,
meaning the roof only has to support 6,000 pounds and not the full 1.5 times the vehicle weight
(in theory). The combination of these factors may increase the likelihood of roof intrusion into
the occupant’s survival space. Individuals 72-in or taller will have less survival space, and this
could increase the likelihood to be fatally injured by the roof intrusion. Other factors, such as the
age of the occupant, seating position or the number of rotations, could also play a role in the
11
probabiliity of being killed
k
in a roollover. Furthher researchh is thereforee needed to examine
e
the
combinattion of thesee factors influuence the prrobability off dying as a function
f
of driver
d
height.
H
Hypotheticall
ly, if the heigght of the drriver did not affect the faatality rate of single vehiicle
rollover accidents,
a
th
hen the fataliity rate for men
m and wom
men would be
b the same as
a their
respectivve height disttributions; shhown in Tabble 6. Assum
ming this to be
b true, it is possible to see
s
which veehicle catego
ories increasee the likelihoood for indivviduals 72-inn or taller dyying in a rolllover
accident. This is acccomplished by
b using the data given in Table 11 and
a Equationn (3) to consstruct
a 95% coonfidence intterval. If thee lower bounnd of the connfidence inteerval exceedds the populaation
percentagge, 19.71% for
f males, thhen males 722-in or taller have an incrreased probaability of dyiing
in that caategory of veehicle. The confidence
c
i
intervals
of the
t different vehicle cateegories are
plotted allong with th
he populationn percentagee as shown inn Figure 1.
Percent Fatality of Individual 6ft or Over
955% Confid
dence Interrvals by Vehicle
V
Cattegory
Vehicle Category
C
Population Percentaage
60
6
50
5
40
4
30
3
20
2
10
0
Vehicle Category
FIGURE
F
1 Confidencee Intervals by
b Vehicle Category
C
t
vehiicle categoriies have an increased fattality rate forr individualss 72Seven of the thirteen
in or talleer; all resultss at statisticaally significaant at the 5%
%-level (all t=
=values≥1.96, p≤0.05). The
high num
mber of vehiccles that havve an increased fatality raate for 72-inn or taller maales is not
surprising when com
mpared to thee free headrooom above thhe driver’s head,
h
shown in Table 5, for
f
the differrent categoriies of vehiclees.
12
SUMMARY AND CONCLUSIONS
The overall conclusion of this paper suggests that an individual 72-in or taller, male or female,
involved in a single-vehicle rollover collision has a greater likelihood of being killed based on
their population percentage than individuals of a height less than this value. More specific
observations are as follows:
• Taller individuals have a greater sitting height and thus less distance between the top of
their head and the bottom of the roof liner. Roof intrusion is probably more likely to
cause severe head and neck injuries due to this decreased distance. However, other
factors could also influence the risk of being killed, as discussed above, and should be
examined further.
• Both men and women, 72-in or taller, are more likely to be killed in a single-vehicle
rollover collision then their respective population percentage. This conclusion was
reached using a 95% confidence interval.
• Vehicles close to or exceeding the 6,000-pound weight limit specified by FMVSS 216,
regardless of the headroom provided, appear to be more risky to individuals 72-in or
taller. The authors believe this occurs due to roofs not able to support the dynamic
rollover weight of the vehicle, leading to increased roof intrusion. This statistic might
begin to decrease as the new regulations imposed by FMVSS 216a are implemented.
It should be pointed out that these results are influenced by an important limitation.
Because FARS only records the height of the driver even if multiple occupants were killed in the
collision, several vehicle categories have very limited data. This creates a higher standard
deviation, which makes the final results not statistically significant for these categories of
vehicles.
Future work in this area show focus on obtaining a larger data set with more detailed
information, such as the number of rotations, the driver’s sitting position, and the medical
condition of the driver. This additional information could also help rule out confounding factors,
such as tall people buying vehicles with larger headroom space. Obtaining data from other
sources, National Automotive Sampling System (NASS) Crashworthiness Data System (CDS),
General Estimates System (GES), National Center for Statistics and Analysis (NCSA) will
increase the number of cases and possibly provide a greater depth of information. Another
avenue of future research would be to calculate the population percentage and number of
individuals killed in single-vehicle rollover accidents for each height increment and for different
age groups. This type of analysis, however, would require a much larger dataset.
REFERENCES
1.
NHTSA. Federal Motor Vehicle Safety Standards, Roof Crush Resistance. U.S.
Department of Transportation, Washington, D.C., Standard No. 216, 1991.
2.
NHTSA. Federal Motor Vehicle Safety Standards, Roof Crush Resistance; Upgraded
Standard. U.S. Department of Transportation, Washington, DC, Standard No. 216a,
2010.
3.
Young, D., Grzebieta, R., Rechnitzer, G., Bambach, M. and Richardson, S. Rollover
Crash Safety: Characteristics and Issues. Proceedings from the 5th International
Crashworthiness Conference (ICRASH2006). Athens, Greece, 2006.
4.
Friedman, D. and Nash, C.E. Advanced Roof Design for Rollover Protection. Paper No.
01-S12-W-94, 2001.
13
5.
6.
7.
8.
9.
10.
11.
12.
Nusholtz, G.S., Melvin, J.W., Huelke, D.F., Alem, N.M. and Blank, J.G. Response of the
Cervical Spine to Superior-Inferior Head Impact. Proceedings of the 25th Stapp Car
Crash Conference, Paper No. 811005, Society of Automotive Engineers, 1981.
Yoganandan, N., Sances Jr, A., Maiman, D.J., Mykebust, J.B., Pech, P. and Larson, S.J.
Experimental Spinal Injuries with Vertical Impact. In Spine, Vol. 11(9), 1986, 855-860.
Partyka, S. Roof Intrusion and Occupant Injury in Light Passenger Vehicle Towaway
Crashes. R. Office of Vehicle Safety Standards, National Highway Traffic Safety
Administration, Washington, D.C., February, 1992.
NHTSA. Federal Motor Vehicle Safety Standards; Roof Crush Resistance. Department of
Transportation, 49 CFR Part 57l, Docket No. NHTSA-1999-5572; Notice 2, RIN 2127AG51, National Highway Traffic Safety Administration, Washington, D.C., 2001.
McDowell, M.A., Fryar, C.D., Ogden, C.L. and Flegal, K.M. Anthropometric Reference
Data for Children and Adults: United States, 2003-2006. Vol. 10, US Deptartment of
Health and Human Services, Centers for Disease Control and Prevention, National Center
for Health Statistics, 2008.
Bardeen, C.R. General Relations of Sitting Height to Stature and of Sitting Height and
Stature to Weight. In American Journal of Physical Anthropology, Vol. 6(4), 1923, 355388.
Top-20 Selling Vehicles in U.S. For 2009. Reuters, 2009.
http://www.reuters.com/article/2010/01/05/autos-usa-chart-idUSN0510644520100105.
Accessed June 2011.
Interior Specifications and Features. MSN Autos, 1999 & 2009.
http://autos.msn.com/research/vip/spec_Interior.aspx. Accessed June 11, 2011.