DOT HS 811 578 March 2012

Lower Extremity Injuries and 

Intrusion in Frontal Crashes 
DISCLAIMER

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Recommended APA Format Citation:

Austin, R. A. (2012, March). Lower Extremity Injuries and Intrusion in Frontal Crashes. (Report 

No. DOT HS 811 578). Washington, DC: National Highway Traffic Safety Administration. 
i

Technical Report Documentation Page

1. Report No. 2. Government Accession No. 3. Recipients Catalog No.

DOT HS 811 578

4. Title and Subtitle 5. Report Date

Lower Extremity Injuries and Intrusion in Frontal Crashes March 2012

6. Performing Organization Code

NVS-421

7. Author(s) 8. Performing Organization Report No.

Rory A. Austin

9. Performing Organization Name and Address 10. Work Unit No.

National Center for Statistics and Analysis

National Highway Traffic Safety Administration

1200 New Jersey Avenue SE. 11. Contract or Grant No.

Washington, DC 20590

12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered

National Center for Statistics and Analysis Technical Report

National Highway Traffic Safety Administration

1200 New Jersey Avenue SE. 14. Sponsoring Agency Code

Washington, DC 20590 NHTSA

15. Supplementary Notes

16. Abstract

Previous studies have shown that lower extremity injuries account for a significant portion of the injuries sustained by 

passenger vehicle drivers in frontal crashes, and this pattern continues to hold for newer model year vehicles. This paper 

explores the potential causal factors associated with the risk of moderate or more severe lower extremity injuries in 

frontal crashes with a particular emphasis on the role of intrusion. A categorical analysis of the relationship between 

floor and toe pan intrusion showed that higher levels of intrusion were related to a larger percentage of lower leg injuries. 

A categorical analysis of the relationship between instrument panel and knee bolster intrusion and upper leg injuries was 

less clear but still demonstrated that vehicles with any intrusion had a higher percentage of upper leg injuries than 

vehicles with no intrusion. Logistic regression models were used to estimate the independent effect of intrusion on the 

probability of lower extremity injuries while controlling for crash severity (change in velocity), age, gender, body mass 

index, vehicle age and vehicle body type. The results indicated that for all frontal crashes the odds of experiencing a 

lower leg injury when floor or toe pan intrusion occurred were twice the odds of experiencing a similar injury without 

intrusion. In full frontal crashes and in left offset and small overlap impact crashes, the lower leg injury odds ratios for 

intrusion versus no intrusion increased to seven. For all frontal crashes the odds of experiencing an upper leg injury 

when instrument panel or knee bolster intrusion occurred were four times the odds of experiencing a similar injury 

without intrusion. The upper leg injury odds ratios for intrusion versus no intrusion increased to eight in full frontal 

crashes and to 17 in left offset and small overlap impact crashes. 

17. Key Words 18. Distribution Statement: 

NASS-CDS, frontal crashes, offset, injuries, lower 

extremity, leg

This report is available from the National Technical 

Information Service www.ntis.gov

19. Security Classification (of this report) 20. Security 

Classification (of 

this page) 

21. No. of Pages 22. Price

UNCLASSIFIED UNCLASSIFIED 23

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized
ii

Table of Contents

List of Tables.................................................................................................................iii

EXECUTIVE SUMMARY ............................................................................................. 1

1. INTRODUCTION....................................................................................................... 2

2. APPROACH AND DATA .......................................................................................... 3

3. LOWER EXTREMITY INJURIES ............................................................................. 4

4. INTRUSION............................................................................................................... 6

5. INTRUSION, DELTA-V AND INJURY: SIMPLE MODELS.................................... 8

6. INTRUSION AND INJURY: MULTIVARIATE MODELS ..................................... 10

7. DISCUSSION AND CONCLUSIONS...................................................................... 14

References .................................................................................................................... 16

Appendix ...................................................................................................................... 17
iii

List of Tables

Table 1: Descriptive Statistics for Possible Predictors of Lower Extremity Injuries.....................4

Table 2: Frontal Damage Types...................................................................................................4

Table 3: Injury Source for MAIS 2+ Lower Leg Injuries.............................................................5

Table 4: Presence and Severity of Lower Leg Injuries From Floor or Foot Controls....................5

Table 5: Injury Source for MAIS 2+ Upper Leg Injuries .............................................................6

Table 6: Presence and Severity of Upper Leg Injuries From Instrument Panel/Knee Bolster........6

Table 7: Presence of Intrusion by Damage Type..........................................................................7

Table 8: Magnitude of Intrusion by Damage Type.......................................................................8

Table 9: Injuries by Intrusion ......................................................................................................9

Table 10: Injuries by Change in Velocity ....................................................................................9

Table 11: Logistic Regression Results for the Probability of Driver Having Lower

Leg Injury ................................................................................................................................ 11

Table 12: Logistic Regression Results for the Probability of Driver Having Upper 

Leg Injury ................................................................................................................................. 13

Table 13: Summary of Odds Ratios for Intrusion and Injury...................................................... 15

Table 14: Detailed Lower and Upper Leg Injuries..................................................................... 17

Table 15: Injuries by Frontal Damage Type............................................................................... 17
1

EXECUTIVE SUMMARY

Previous studies have shown that lower extremity injuries account for a significant portion of the injuries 

sustained by passenger vehicle drivers in frontal crashes, and this pattern continues to hold for newer 

model year vehicles. This paper explores the factors associated with the risk of moderate or more severe 

lower extremity injuries in frontal crashes with a particular emphasis on the role of intrusion. 

An examination of the moderate or more severe lower leg injuries experienced by these drivers revealed 

that the floor or foot control was the source of an estimated 93 percent of the injuries. A similar 

examination of upper leg injuries found that the instrument panel or knee bolster was the source of an 

estimated 87 percent of the injuries. Overall an estimated 3.5 percent of belted drivers of model year 

1998 through 2010 vehicles in frontal crashes where the vehicle was towed due to damage experienced a 

lower leg injury of moderate or higher severity from the floor or foot control, and 1.5 percent experienced 

an upper leg injury of moderate or more severity from the instrument panel or knee bolster.

Based upon these results, this report focused on injuries from these sources and intrusion of the floor, toe 

pan, instrument panel and knee bolster. Floor and toe pan intrusion into the driver’s seating position 

occurred in an estimated 2 percent of all vehicles in frontal crashes. Among frontal damage types, floor 

and toe pan intrusion was most likely to occur in a left side small overlap impact (SOI) at an estimated 6 

percent. Instrument panel and knee bolster intrusion into the driver’s seating position occurred in an 

estimated 3 percent of all vehicles in frontal crashes with intrusion most likely to occur in left offsets at an 

estimated 8 percent.

A categorical analysis of the relationship between floor and toe pan intrusion showed that higher levels of 

intrusion were related to a larger percentage of lower leg injuries. A categorical analysis of the 

relationship between instrument panel and knee bolster intrusion and upper leg injuries was less clear but 

still demonstrated that vehicles with any intrusion had a higher percentage of upper leg injuries than 

vehicles with no intrusion.

Logistic regression models were used to estimate the independent effect of intrusion on the probability of 

lower extremity injuries while controlling for crash severity (delta-V), age, gender, body mass index, 

vehicle age and vehicle body type. A total of twelve statistical models were estimated based upon two 

dependent variables (lower leg injuries and upper leg injuries), two measures of intrusion (continuous 

intrusion measures and an indicator variable for the presence of intrusion), and three damage types (all 

frontals, full frontals, and left offset and SOI).

Overall the results from the logistic models indicated a statistically significant positive effect of intrusion 

on the likelihood of lower extremity injuries even when controlling for delta-V as well as driver and 

vehicle characteristics. The results indicated that for all frontal crashes the odds of experiencing a lower 

leg injury when floor or toe pan intrusion occurred were twice the odds of experiencing a similar injury 

without intrusion. In full frontal crashes and left offset and SOI crashes, the lower leg injury odds ratios

for intrusion versus no intrusion increased to seven. Furthermore, the models indicated that each 

additional centimeter of intrusion increased the odds of lower leg injury by an estimated 14 percent in full 

frontals and 5 percent in left offset and SOI crashes. Overall the odds of experiencing an upper leg injury 

when instrument panel or knee bolster intrusion occurred were four times the odds of experiencing a 

similar injury without intrusion. The upper leg injury odds ratios for intrusion versus no intrusion 

increased to eight in full frontal crashes and to 17 in left offset and SOI crashes. The models also 

indicated that each additional centimeter of intrusion increased the odds of upper leg injury by about 5 

percent in these two damage types.
2

1. INTRODUCTION

Previous studies have shown that lower extremity injuries account for a significant portion of the injuries 

sustained by passenger vehicle drivers in frontal crashes (Kuppa et al. 2001), and this pattern continues to 

hold for newer model year vehicles. According to the 2009 National Automotive Sampling System –

Crashworthiness Data System (NASS-CDS), an estimated 37 percent of the moderate or more severe 

injuries experienced by drivers of model year 2003 through 2010 passenger vehicles towed due to damage 

in frontal crashes affect the lower extremities. An estimated 26 percent of the serious or more severe 

injuries to this same group affect the lower extremities. Furthermore, since many of these injuries are not 

life-threatening, their severity as measured on the Abbreviated Injury Scale (AIS) may not fully reflect the 

physical disabilities and psychological effects of these injuries (Read et al. 2004). This paper explores the 

potential causal factors associated with the risk of moderate or more severe lower extremity injuries in 

frontal crashes with a particular emphasis on the role of intrusion. 

Understanding the role of intrusion in predicting lower extremity injuries is complicated because of the 

large number of possible explanatory factors. In an overview of lower extremity injuries in frontal 

crashes, Rudd (2009) found that the risk of leg, ankle, and foot injuries generally increased with higher

levels of toe pan intrusion. However, in additional to toe pan intrusion, Rudd also considered both 

characteristics of the occupants such as age, gender, height and seating position as well as characteristics 

of the vehicles such as body type (passenger car versus light truck and van), model year, frontal damage 

type (offset versus full frontal), and crash severity as measured by the change in velocity (delta-V). Rudd 

implicitly controlled for restraint use by only examining properly belted occupants. All of these variables 

are available in the NASS-CDS, and this report considers many of the same factors. 

While toe pan intrusion has been correlated with lower extremity injuries in previous studies (Eigen &

Glassbrenner 2003, Crandall et al. 1995), this report takes a more broad view. The analysis first explores

the vehicle components that are the most common source of lower extremity injuries and then estimates 

the relationship between intrusion of these components and the risk of injury. However, since the role of 

intrusion in lower extremity injuries is complicated by the fact that crash severity is correlated with 

intrusion as well as injury risk, a multivariate statistical model containing intrusion in addition to other

factors also is presented to separate out the independent contribution of intrusion. 

There are some factors that have been shown to be correlated with the risk of foot and ankle injuries that 

are not considered in this study including foot placement, size of foot and type of shoe (Crandall et al.

1996). While these factors may be important for completely understanding the causal mechanism, the 

primary purpose of this report is to test whether intrusion is correlated with lower extremity injuries. The 

consideration of additional factors is intended primarily to control for and rule out competing 

explanations; it is not meant to provide a complete explanation of the injury mechanism. 

A second consideration is that the effect of intrusion may be conditional on frontal damage type. 

Intrusion may be more important in some frontal damage types than in others, and the relationship 

between intrusion and lower extremity injuries may be obscured by combining all frontal damage types. 

Therefore this report explores this possibility by presenting results for all frontal damage types as well as 

for particular subsets of frontal crashes. 
3

2. APPROACH AND DATA

Crashes included in this analysis are a subset of the NASS-CDS sample from 1997 through 2009. The 

vehicles selected were passenger vehicles towed due to damage of model year 1998 through 2010. The 

vehicles were inspected by a NASS-CDS researcher and were not involved in a rollover. For most of the 

vehicles, the general area of damage of the highest deformation location was the front. However, some 

cases with a general area of damage of right or left were included because they fit the Medical College of 

Wisconsin definition of a frontal small overlap impact (SOI), which uses the Collision Deformation 

Classification and crush profiles (Halloway et al. 2011). Frontal impact crashes that were not SOIs were 

classified according to the width and location of the direct damage into either right or left frontal offset, 

full frontal or center damage modes. Direct damage that encompassed and likely engaged both frame 

rails based upon the average location of the rails for the vehicle class were classified as full frontal 

damage. Direct damage that covered only one frame rail was identified as an offset, and direct damage 

that occurred between the two frame rails was considered center damage. 1

 

Also, the vehicle had to have a known total delta-V to control for crash severity. Finally, to avoid the 

possible influence of an extreme outlier, one case with a total change of velocity of 155 kilometers per 

hour was excluded since it was over 25 kph greater than the next highest value. After applying all of 

these vehicle restrictions, there were 10,424 vehicles.

To simplify the analysis of injuries and to control for seating position, only the driver was examined, and 

a handful of cases were dropped because the driver seat was not on the left of the vehicle. Drivers had to 

be restrained by three-point belts and have known injury outcomes, age, height, and weight. 2

 Age was

used for predicting the probability of a lower extremity injury in the statistical models, and height and 

weight were needed to compute the body mass index (BMI), which was also a predictor in the statistical 

models.

Descriptive statistics for the above variables revealed that a few cases had extreme values. Cases with 

extreme values were excluded to avoid possible outliers from having a usually large effect on the 

statistical results. Drivers younger than 16 years old and ones with a calculated BMI of less than 16 or 

greater than 50 were excluded. Many of the unusually low and high BMI values appeared to involve 

incorrectly recorded weights or heights, but it was not possible to determine definitely which values, if 

any, were incorrect. Therefore, the decision was made to exclude drivers identified as severely 

underweight or severely obese based upon the calculated BMI. 

The final data set for analysis contained 7,284 vehicles and drivers involved in 6,938 crashes. Overall, an 

estimated 52 percent of the drivers were women. The vehicle body types were an estimated 66 percent

passenger cars and the remainder were LTVs (light trucks and vans). The 34 percent that were LTVs 

included an estimated 16 percent utility vehicles, 7 percent vans, and 11 percent pickups. Table 1 

provides summary statistics for the other variables used in this report. 

 1 A total of 45 vehicles with frontal damage were dropped from the analysis because they could not be classified, usually because 

they had direct damage outside of the frame rails but crush on both corners and thus did not fit any of the defined damage types. 2 A total of 236 drivers in model year 1998 and 1999 vehicles from the 2009 file were not included because it was the first year 

NASS-CDS began restricting collection of injury outcomes to occupants of vehicles ten years old or newer. 
4

Table 1: Descriptive Statistics for Possible Predictors of Lower Extremity Injuries

Weighted 

Average

Minimum Maximum

Total delta-V (kph) 21 5 129

Model Year 2001 1998 2010

Age of Driver 37 16 97

BMI of Driver (kg/m2) 26.2 16.1 50.0

Source: NASS-CDS 1997-2009; weighted total = 2,753,917; sample size = 7,284

Table 2 provides an overview of the types of frontal damage included in the analysis based upon the 

classification described above. The most frequent frontal damage type in the report is a full frontal crash,

where it is likely that the crash engaged both frame rails, and this type accounts for an estimated 42

percent of the vehicles. The second most frequent frontal damage type is a left offset, where it is likely 

that the crash engaged the frame rail on the driver’s (left) side of the vehicle, for an estimated 20 percent. 

A left SOI, where the crash occurred on the driver’s side and likely did not engage any frame rails, 

accounted for an estimated 10 percent. The least frequent type of damage, accounting for an estimated 

3 percent of the vehicles, was center damage likely to be a collision with a narrow object between the two 

frame rails.

Table 2: Frontal Damage Types

Damage Type Weighted Percent

Center 3%

Full Frontal 42%

Left Offset 20%

Left Small Overlap Impact (SOI) 10%

Right Offset 17%

Right Small Overlap Impact (SOI) 8%

Total 100%

Source: NASS-CDS 1997-2009; weighted total = 2,753,917; sample size = 7,284

3. LOWER EXTREMITY INJURIES

Lower extremity injuries in this analysis were divided into lower and upper leg injuries. Lower leg 

injuries involve the foot and the leg below the knee; upper leg injuries involve the knee, thigh and pelvis. 

The regions of lower and upper leg were assigned based upon the body region codes of the Abbreviated 

Injury Scale-85 (AIS-85). While NASS-CDS coded the injuries using AIS-90, the body region codes in 

AIS-90 do not separate upper and lower leg injuries. Instead, AIS-90 body region codes only indicate 

“lower extremity.” NASS-CDS, however, also provides the AIS-85 body region that is derived from 

AIS-90 injury coding. The derived AIS-85 body regions that were relevant for this analysis were 

ankle/foot, knee, leg (lower), lower limb(s) (whole or part unknown), pelvic/hip and thigh.3

 

The 7,284 drivers in the sample had a total of 1,577 injuries of AIS severity moderate (2) or higher 

involving the six body regions identified above of which only the 74 listed as “lower limb(s) (whole or 

part unknown)” did not provide enough information to differentiate between upper and lower leg. Two 

approaches were adopted to assign these injuries to either upper or lower leg. One method was to use the 

body region assigned to lower extremity skeletal injuries based upon the complete AIS-90 injury code 

used in Rudd (2009), which was used to assign 44 of the 74 injuries. A second method involved 

 3 While the derived AIS-85 body region was used for classification into upper or lower leg injuries, the AIS-90 

coding was used for severity.
5

reviewing all of the lower extremity injuries. In the 30 reviewed cases, the injury was assigned to upper 

or lower leg based upon clinical review.4

 

Once all the 1,577 injuries were assigned to either the upper or lower leg, only upper and lower leg 

injuries at the maximum AIS severity for each leg region were retained for analysis. For example, if a 

driver had an AIS 2 (moderate) foot/ankle injury, an AIS 2 (moderate) knee injury and an AIS 3 (serious) 

thigh injury, then the AIS 2 foot/ankle injury was retained as the maximum lower leg injury and the AIS 3 

thigh injury was retained as the maximum upper leg injury. Overall, this selection process produced 768 

lower leg injuries and 434 upper leg injuries. The remaining 375 lower extremity injuries were dropped 

because there was a more severe injury for the same leg region.

The next step in the analysis involved determining the component that was the source of the injury. Table 

3 contains the relative frequency of components listed as the injury source of the maximum AIS (MAIS) 

2 and greater lower leg injuries.

Table 3: Injury Source for MAIS 2+ Lower Leg Injuries

Injury Source Component

Weighted 

Percent of 

Injuries

Floor (Including Toe Pan) 68.0%

Foot Controls Including Parking Brake 25.2%

Instrument Panel and Knee Bolster 5.7%

All Other 1.1%

Total 100.0%

Source: NASS-CDS 1997-2009, weighted total = 144,243, sample size = 768

Table 3 indicates that the floor, toe pan and foot controls were the source of an estimated 93 percent of 

the moderate or more severe injuries to the lower leg including the foot and ankle. The instrument panel 

and knee bolster accounted for an estimated 6 percent, and no other component accounted for more than 

1 percent. The remainder of this analysis focuses on injuries where floor or foot controls was listed as the 

injury source. 

Table 4 demonstrates that an estimated 3.5 percent of drivers in this analysis experienced a moderate or 

more severe lower leg injury from floor or foot controls. Among the 3.5 percent who experienced such 

injuries, most of the drivers experienced moderate injuries although a few serious injuries occurred.

Table 4: Presence and Severity of Lower Leg Injuries from Floor or Foot Controls

Injury Severity

Weighted 

Percent of 

Drivers

No MAIS 2+ Injury 96.5%

MAIS 2: Moderate 3.3%

MAIS 3: Serious 0.2%

Total 100.0%

Source: NASS-CDS 1997-2009; weighted total = 2,753,917; sample size = 7,284

 4 The clinical review was completed by NHTSA’s Human Injury Research Division.
6

Table 5 contains the relative frequency of components listed as the injury source of the MAIS 2 and 

greater upper leg injuries. Table 5 indicates that the instrument panel and knee bolster are the source of 

87 percent of the moderate or more severe injuries to the upper leg including the knee, thigh and pelvis.5

 

The remaining injuries were split among a variety of different components. The remainder of this 

analysis is focused on injuries where the instrument panel or knee bolster was listed as the injury source. 

 

Table 5: Injury Source for MAIS 2+ Upper Leg Injuries

Injury Source Component

Weighted 

Percent of 

Injuries

Instrument Panel and Knee Bolster 87.4%

Left Hardware 4.2%

Left Interior 1.8%

Floor (Including Toe Pan) 1.8%

Floor or Console Transmission Lever 1.4%

Steering Wheel 1.1%

All Others 2.3%

Total 100.0%

Source: NASS-CDS 1997-2009, weighted total = 53,301, sample size = 434

Table 6 demonstrates that an estimated 1.5 percent of drivers in this analysis experienced a moderate or 

more severe upper leg injury from the instrument panel or knee bolster. Among the 1.5 percent who 

experienced such an injury, most of the drivers experienced moderate injuries although a few serious and 

severe injuries occurred. (More details regarding the lower and upper leg injury counts may be found in 

Table 14 in the Appendix.)

Table 6: Presence and Severity of Upper Leg Injuries From Instrument Panel/Knee Bolster

Injury Severity

Weighted 

Percent of 

Drivers

No MAIS 2+ injury 98.5%

MAIS 2: Moderate 1.1%

MAIS 3: Serious 0.4%

MAIS 4: Severe <0.1%

Total 100.0%

Source: NASS-CDS 1997-2009; weighted total = 2,753,917; sample size = 7,284

4. INTRUSION

The previous section demonstrated that the components most likely to be associated with lower extremity 

injuries are the floor and foot controls for lower leg injuries and the instrument panel and knee bolster for 

upper leg injuries. Therefore, the intruding components associated with these injury sources were 

selected for further study. For lower leg injuries, the intruding components of interest were the floor pan 

 5 The components of instrument panel and knee bolster were combined for all years of NASS-CDS because they 

share the same component code in some of the years.
7

(including sill) and the toe pan. For upper leg injuries, the intruding component of interest was the 

instrument panel and knee bolster.

To compute the level of intrusion, all intrusions of the floor pan, toe pan, instrument panel and knee 

bolster assigned to the front left (driver) seat were selected. For 6,802 vehicles, there was no intrusion of 

the floor or toe pan of three centimeters (cm) or greater assigned to the driver’s seating position.

6

 In 450 

cases the maximum floor or toe pan intrusion, ranging from 3 to 106 cm, was retained. For the remaining 

32 vehicles, the maximum intrusion was a range rather than an exact measure. In these cases the measure 

of intrusion was imputed by replacing the range with the estimated average intrusion of known values 

within the same range. Similarly, for 6,969 vehicles, there was no relevant intrusion of the instrument 

panel or knee bolster. In 280 cases the maximum instrument panel or knee bolster intrusion, ranging from 

3 to 92 cm, was retained. For the remaining 35 vehicles, the maximum intrusion was imputed by 

replacing the range with the estimated average. 

Table 7 contains estimates of the percent of vehicles with relevant intrusion, and Table 8 reports the 

amount of intrusion when it occurs. Overall, floor or toe pan and instrument panel or knee bolster 

intrusion into the drivers’ seating positions are relatively rare in frontal crashes. Floor or toe pan intrusion 

occurred in an estimated 2 percent of the towed vehicles with frontal damage, and instrument panel or 

knee bolster intrusion occurred in an estimated 3 percent of the vehicles. Table 7 also demonstrates that 

intrusion is related to the frontal damage type with collisions on the right side of the vehicle rarely 

resulting in relevant intrusions for the driver’s seating position. The frontal damage type most likely to 

have floor or toe pan intrusion is a left small overlap impact, and the type most likely to have instrument 

panel or knee bolster intrusion is a left offset crash. The second most common type of frontal damage

with floor or toe pan and instrument panel or knee bolster intrusion was a center crash where the damage 

was concentrated between the two frame rails. When intrusion does occur, Table 8 shows that the largest 

estimated floor or toe pan intrusion occurs with center and left offset damage, and the largest estimated 

instrument or knee panel intrusion occurs with left offset damage.

Table 7: Presence of Intrusion by Damage Type

Damage Type

Weighted Percent With 

Floor or Toe Pan 

Intrusion

Weighted Percent With 

Instrument Panel or 

Knee Bolster Intrusion

Sample 

Size

Center 5% 4% 358

Full Frontal 1% 1% 3,078

Left Offset 3% 8% 1,325

Left SOI 6% 2% 751

Right Offset/SOI7 <1% <1% 1,772

Total 2% 3% 7,284

Source: NASS-CDS 1997-2009; weighted total = 2,753,917

 6 NASS-CDS data collection rules do not require the coding of intrusions of 2 cm or less, which is approximately 

less than 1 inch. 7 Right offset and SOI are combined due to the small number of cases of intrusion in each category.
8

Table 8: Magnitude of Intrusion by Damage Type

Damage Type

Weighted Average 

Floor or Toe Pan 

Intrusion When It 

Occurs (cm)

Sample 

Size 

With 

Intrusion

Weighted Average 

Instrument Panel 

or Knee Bolster 

Intrusion When It 

Occurs (cm)

Sample 

Size 

With 

Intrusion

Center 17 61 13 45

Full Frontal 12 156 11 96

Left Offset 16 134 40 81

Left SOI 12 104 13 61

Right Offset/SOI5 6 27 7 32

Total 13 482 30 315

Source: NASS-CDS 1997-2009; weighted total (floor/toe pan intrusion) = 57,764; 

weighted total (instrument panel/knee bolster intrusion) = 69,864

5. INTRUSION, DELTA-V AND INJURY: SIMPLE MODELS

As demonstrated in the previous section, moderate or more severe injuries to the lower extremities among

belted drivers in all NASS-CDS frontal crashes occur in relatively small proportions of crashes. An 

estimated 3.5 percent of drivers experienced lower leg injuries from the floor or foot controls, and an 

estimated 1.5 percent of drivers experienced upper leg injuries from the instrument panel or knee bolster. 

In spite of these relatively small proportions, it may still be the case that these injuries are more likely for 

some crash situations and some occupants than for others. This section explores the relationship between 

lower and upper injuries, intrusion, and crash severity as measured by delta-V.

Table 9 demonstrates the relationship between intrusion and the estimated percent of drivers with a 

relevant injury.8

 The estimated percentages in Table 9 indicate that the percent of drivers with a lower leg 

injury from floor or foot controls generally increases as the maximum intrusion from the floor or toe pan 

increases. Table 9 also indicates that the estimated percent of drivers with an upper leg injury from the 

instrument panel or knee bolster is greater when instrument panel intrusion occurs, but the category with 

the most intrusion (20 to 106 cm) has a lower estimated percent than the other categories with intrusion. 

The reason appears to be that a case with more than 19 cm of instrument panel intrusion and no injury has 

a very large sample weight compared to the rest of the cases in the category (36,537 versus a median of 

22) even though the category contains 91 observations. That said the differences across the intrusion 

categories are statically significant at conventional (0.05) levels for both lower and upper leg injuries as 

indicated by the results of the modified Rao-Scott chi-square test.

 8 The intrusion category of 20 cm to 106 cm is not divided into categories with smaller ranges because of the 

relatively small sample size.
9

Table 9: Injuries by Intrusion

Amount of 

Intrusion

Drivers With Lower Leg Injuries 

From Floor or Foot Controls

By Floor and Toe Pan Intrusion

Drivers With Upper Leg Injuries From 

Instrument Panel or Knee Bolster

By Instrument Panel and Knee Bolster Intrusion

Weighted Percent of Drivers With 

Moderate or More Severe Injuries

Sample 

Size

Weighted Percent of Drivers With 

Moderate or More Severe Injuries

Sample 

Size

None 3.3% 6,802 1.3% 6,969

3 to 9 cm 5.7% 191 20.1% 136

10 to 19 cm 17.3% 154 21.4% 88

20 to 106 cm 23.9% 137 4.3% 91

Any Intrusion 13.3% 482 10.0% 315

Total 3.5% 7,284 1.5% 7,284

Source: NASS-CDS 1997-2009; weighted total = 2,753,917

Modified Rao-Scott Chi-Squared Test, Pr < 0.01 (lower leg), Pr < 0.01(upper leg)

Intrusion is not the only factor that may be related to the estimated percent of drivers with a relevant 

injury. One such factor that has a strong relationship with injury is delta-V. Furthermore, since intrusion 

and crash severity are likely to be related, it is important to consider the independent effect of delta-V. 

Table 10 demonstrates the relationship between delta-V and the estimated percent of drivers with a 

relevant injury. The table generally shows that as the change in velocity increases, the estimated percent 

of drivers with a relevant injury also increases. This finding confirms the importance of delta-V for 

predicting injuries and the need to control for delta-V when exploring the role of intrusion. 

Table 10: Injuries by Change in Velocity

delta-V

(kph)

Drivers w/ Lower Leg Injuries From 

Floor or Foot Controls

Drivers w/ Upper Leg Injuries 

From Instrument Panel or Knee 

Bolster 

Sample Size

Weighted Percent of Cases With 

Moderate or More Severe Injuries

Weighted Percent of Cases With 

Moderate or More Severe Injuries

5-19 3.5% 0.6% 2,941

20-29 1.5% 1.0% 2,415

30-39 4.0% 4.5% 1,099

40-49 14.5% 3.0% 443

50-59 20.8% 13.6% 211

60-69 35.0% 23.1% 95

70-129 16.1% 35.1% 80

Total 3.5% 1.5% 7,284

Source: NASS-CDS 1997-2009; weighted total = 2,753,917

Note: Modified Rao-Scott Chi-Squared Test, Pr <0.01 (lower leg), Pr < 0.01(upper leg)

A third table was run to examine whether significant differences existed in the estimated percent of 

drivers with relevant injuries across the six frontal damage types. The estimates did not indicate any 

noticeable patterns, and the results of modified chi-squared tests indicated that the differences across the 

damage types were not statistically significant at the conventional 0.05 level. Therefore, the results are 

not discussed in the body of this report but are presented in Table 15 in the Appendix. 
10

6. INTRUSION AND INJURY: MULTIVARIATE MODELS

The previous section demonstrated that larger amounts of floor or toe pan intrusion and higher changes in 

velocity were correlated with higher rates of lower leg injuries in passenger vehicles towed due to damage 

in frontal crashes. The previous section also demonstrated that the presence of instrument panel intrusion 

and higher changes in velocity were correlated with higher rates of upper leg injuries. However, there are 

many other factors that may affect the risk of lower extremity injuries. In additional to testing the 

hypotheses related to intrusion and delta-V, the statistical models also consider the following hypotheses

based upon previous studies: 

• Driver Age: Older drivers are more likely to experience lower extremity injuries than younger 

drivers.

• Driver Gender: Women are more likely to experience lower extremity injuries than men. 

• Driver BMI: Drivers with higher BMIs are more likely to experience lower extremity injuries

than those with lower BMIs. 

• Vehicle Age: Newer vehicles (those from model year 2003 and later) are likely to produce 

different injury patterns than older vehicles (model year 1998 through 2002).

• Vehicle Type: Light trucks and vans (LTVs) are likely to produce different injury patterns than 

passenger cars.

The multivariate statistical method selected for this analysis was logistic regression where the dependent 

variable was whether a moderate or more severe (AIS 2 or greater) injury occurred (1 = yes, 0 = no). One 

set of results is presented for floor and toe pan intrusion and lower leg injuries. Another set of results is 

presented for instrument panel and knee bolster intrusion and upper leg injuries. Two measures of 

intrusion are considered. One is a continuous variable where no intrusion is recorded as zero and all other 

intrusions retain their actual values, and the other is an indicator variable where zero represents no 

intrusion and one represents the presence of intrusion. Finally, all of the logistic models are estimated for 

all frontal crashes, for the subset of full frontal crashes, and for the subset of left offset and SOI crashes. 

Table 11 presents the results for lower leg injuries, and the results in Table 12 are for upper leg injuries.

The results for lower leg injuries in Table 11 support most of the hypotheses. Older drivers are more 

likely to experience lower leg injuries than their younger counterparts in all six versions of the model. 

Female drivers are more likely to experience lower leg injuries than their male counterparts in five of the 

six models. BMI has a statistically significant positive effect on the risk of lower leg injuries in the model 

involving all frontals and full frontals but did not have a statistically significant effect in left offsets and 

SOIs. Neither the age of the vehicle (newer versus older) nor the body type (LTV versus car) produced a 

consistent set of results although drivers of newer vehicles appeared less likely to experience injuries than 

drivers of older vehicles at a statistically significant rate for all frontal crashes.

The results for intrusion and delta-V are more complex. For all frontal crashes, intrusion as a continuous 

variable has a statistically significant positive effect at the 0.10 level, and intrusion as an indicator 

variable has a statistically significant positive effect at the 0.05 level. The fact that the effect of intrusion 

is more statistically significant with an indicator variable than with the continuous variable is not 

surprising. It is easier for the model to demonstrate, and there is more “confidence” in the result, that any 

intrusion is more likely to increase the risk of injury versus no intrusion than it is for the model to 

demonstrate that one additional centimeter of intrusion is more likely to increase the risk of injury. 

However intrusion is a statistically significant predictor of lower leg injury in both models of full frontal 

damage and left offset/SOI damage. The model appears to have an easier time identifying the 

independent effect of intrusion after removing the collisions that occur on the right sides of the vehicles, 

which are away from the drivers.
11

Table 11: Logistic Regression Results for the Probability of Driver Having Lower Leg Injury

Floor/Toe Pan Intrusion in cm

(0 for no intrusion)

Floor/Toe Pan Intrusion Indicator 

(1=yes, 0=no)

Estimated 

Coefficient

Prob. >

Chi-Squared

Estimated 

Odds Ratio

Estimated 

Coefficient

Prob. >

Chi-Squared

Estimated 

Odds Ratio

All Frontal 

Crashes

Intercept -10.550 <.0001 -10.567 <.0001

Intrusion 0.048 0.0823 1.05 0.701 0.0386 2.02

Total Delta-V 0.049 0.2135 1.05 0.051 0.1549 1.05

Age 0.030 0.0014 1.03 0.030 0.0015 1.03

Female

(1=yes, 0=no) 1.962 <.0001 7.12 1.942 <.0001 6.97

BMI 0.131 <.0001 1.14 0.132 <.0001 1.14

Newer Vehicle 

(1=yes, 0=no) -1.267 0.0248 0.28 -1.268 0.0227 0.28

Light Truck or Van 

(1=yes, 0=no) 0.151 0.3299 1.16 0.166 0.2890 1.18

Full Frontal

Damage

Intercept -10.300 <.0001 -10.259 <.0001

Intrusion 0.128 0.0129 1.14 1.967 0.0480 7.15

Total Delta-V -0.026 0.7311 0.98 -0.027 0.7266 0.97

Age 0.042 0.0008 1.04 0.042 0.0009 1.04

Female

(1=yes, 0=no) 1.535 0.0183 4.64 1.536 0.0174 4.64

BMI 0.132 <.0001 1.14 0.131 <.0001 1.14

Newer Vehicle 

(1=yes, 0=no) -1.039 0.2702 0.35 -1.019 0.2781 0.36

Light Truck or Van 

(1=yes, 0=no) -0.016 0.9612 0.98 0.000 0.9988 1.00

Left Offset/SOI

Damage

Intercept -10.497 <.0001 -9.903 <.0001

Intrusion 0.052 0.0123 1.05 1.935 0.0004 6.92

Total delta-V 0.097 <.0001 1.10 0.092 <.0001 1.10

Age 0.025 0.0034 1.03 0.019 0.0328 1.02

Female

(1=yes, 0=no) 0.576 0.0274 1.78 0.356 0.2663 1.43

BMI 0.037 0.2102 1.04 0.033 0.2079 1.03

Newer Vehicle 

(1=yes, 0=no) 0.182 0.7039 1.20 0.271 0.5504 1.31

Light Truck or Van 

(1=yes, 0=no) 0.075 0.8392 1.08 -0.022 0.9501 0.98

Source: NASS-CDS 1997-2009, All frontals N = 7,284, Full frontal N=3,078, Left Offset/SOI N=2,076

Note: Coefficients in bold are statistically significant at the 0.05 level.

In the models of all frontal crashes and full frontals, the effect of delta-V is not statistically significant at 

conventional levels. This result requires explanation. Tables 9 and 10 suggest that intrusion and delta-V 

both predict injuries. It is also is the case that intrusion and delta-V are highly correlated. The weighted 

average of delta-V when floor or toe pan intrusion occurs is 35 kph versus 21 kph when no intrusion 
12

occurs.9 Therefore, it is likely that the model results are affected by near multicollinearity. In other 

words, the model has trouble determining the independent effect of delta-V separate from intrusion. Near 

multicollinearity frequently results in neither variable demonstrating a statistically significant effect

because the variables each have very little “independent” effect, but in this instance intrusion (at least in 

three of the four models) was able to achieve statistical significance at conventional levels. This finding 

suggests that intrusion is a slightly better predictor of injury than delta-V, but it does not mean that deltaV is unimportant. It only means that in this sample, delta-V did not have enough independent explanatory 

power left after controlling for intrusion for it to achieve statistical significance. 

It may be the case that intrusion had more explanatory power than delta-V because change in velocity is a 

continuous variable where intrusion was either treated as dichotomous or was nearly dichotomous (since 

most cases did not have any intrusion). In other words, the rather gross nature of intrusion may make it 

easier for the variable to predict injury, and thus have more explanatory power, than the finer measure of

severity captured by delta-V. However, in the model of left offset/SOI damage, both intrusion and deltaV have the expected statistically significant positive effects on the predicted probability of lower leg 

injuries.

The results in Table 12 for upper leg injuries provide less consistent support for the hypotheses than the

models of lower leg injuries. Older drivers are more likely to experience upper leg injuries than their 

younger counterparts with full frontal and with left offset/SOI damage, but the estimated effect did not 

achieve statistical significance in the model of all frontals. BMI has a statistically significant positive 

effect on the risk of upper leg injuries in the model involving all frontals and full frontal damage but did 

not have a statistically significant effect in left offset/SOI damage. Female drivers are more likely to 

experience upper leg injuries than their male counterparts for all frontal crashes, but the result did not 

hold in the models of full frontal or left offset/SOI damage. Neither the age of the vehicle (newer versus 

older) nor the body type (LTV versus car) produced a consistent set of results although drivers of newer 

vehicles appeared less likely to experience injuries than drivers of older vehicles at a statistically 

significant rate for left offset/SOI damage. 

The results for delta-V and intrusion are less complicated for the models of upper leg injuries than those 

for lower leg injuries. Delta-V has a statistically significant positive effect on the predicted probability of 

upper leg injury in all six models. Intrusion as a continuous measure does not have a statistically 

significant effect at conventional levels for all frontal crashes, but the indicator variable for intrusion has a 

statistically significant positive effect on upper leg injuries. As discussed for lower leg injuries, it is 

easier for the model to demonstrate that any intrusion is more likely to increase the risk of injury versus 

no intrusion than it is for the model to demonstrate that one additional centimeter of intrusion is more 

likely to increase the risk of injury. However, in the models for full frontal and left offset/SOI damage, 

both continuous intrusion and the presence of intrusion have a statistically significant positive effect on 

the predicted probability of injury. 

Overall, the results from the models of upper leg injuries are not as consistent as the results for lower leg 

injuries. This result is likely due to the fact that there is less variation for the models of upper leg injuries 

to explain than in the models of lower leg injuries. Upper leg injuries only affect 1.5 percent of the 

drivers, while lower leg injuries affect 3.5 percent of drivers. 

 9 The traditional colinearity measure of R-squared is not appropriate in this situation since most of intrusion values 

are zero.
13

Table 12: Logistic Regression Results for the Probability of Driver Having Upper Leg Injury

Instrument Panel

Intrusion in cm (0 for no intrusion)

Instrument Panel

Intrusion Indicator (1=yes, 0=no)

Estimated 

Coefficient

Prob. >

Chi-Squared

Estimated 

Odds Ratio

Estimated 

Coefficient

Prob. >

Chi-Squared

Estimated 

Odds Ratio

All Frontal 

Crashes

Intercept -9.2087 <.0001 -9.0773 <.0001

Intrusion 0.0246 0.1608 1.03 1.4347 0.0018 4.20

Total delta-V 0.0797 <.0001 1.08 0.0744 <.0001 1.08

Age 0.0095 0.3390 1.01 0.0086 0.4088 1.01

Female

(1=yes, 0=no) 0.6512 0.0362 1.92 0.6313 0.0508 1.88

BMI 0.0847 0.0005 1.09 0.0851 0.0005 1.09

Newer Vehicle 

(1=yes, 0=no) -0.4859 0.2871 0.62 -0.5142 0.2377 0.60

Light Truck or Van 

(1=yes, 0=no) -0.0249 0.9572 0.98 -0.0550 0.8997 0.95

Full Frontal

Crashes

Intercept -11.439 <.0001 -11.141 <.0001

Intrusion 0.049 0.0312 1.05 2.117 <.0001 8.31

Total delta-V 0.065 <.0001 1.07 0.056 <.0001 1.06

Age 0.022 0.0059 1.02 0.019 0.0187 1.02

Female

(1=yes, 0=no) 0.202 0.5623 1.22 0.167 0.6250 1.18

BMI 0.135 0.0022 1.15 0.136 0.0015 1.15

Newer Vehicle 

(1=yes, 0=no) 0.276 0.5801 1.32 0.242 0.6349 1.27

Light Truck or Van 

(1=yes, 0=no) 0.389 0.5407 1.48 0.431 0.4873 1.54

Left Offset/SOI

Crashes

Intercept -9.020 <.0001 -7.672 <.0001

Intrusion 0.041 0.0129 1.04 2.851 <.0001 17.30

Total delta-V 0.077 <.0001 1.08 0.066 0.0005 1.07

Age 0.035 0.0001 1.04 0.033 0.0017 1.03

Female

(1=yes, 0=no) 0.500 0.2139 1.65 0.238 0.6401 1.27

BMI 0.005 0.9253 1.01 -0.031 0.5199 0.97

Newer Vehicle 

(1=yes, 0=no) -1.704 0.0013 0.18 -2.236 <.0001 0.11

Light Truck or Van 

(1=yes, 0=no) 1.345 0.0677 3.84 1.420 0.0738 4.14

Source: NASS-CDS 1997-2009, All frontals N = 7,284, Full frontal N=3,078, Left Offset/SOI N=2,076

Note: Coefficients in bold are statistically significant at the 0.05 level.
14

7. DISCUSSION AND CONCLUSIONS

As stated in the introduction, this paper aims to explore the potential causal factors associated with the 

risk of moderate or more severe lower extremity injuries in frontal crashes with a particular emphasis on 

the role of intrusion. Establishing these relationships can be difficult for a variety of reasons. One is that 

the dependent variables of interest have relatively low estimated proportions among belted drivers in 

model year 1998 vehicles that were towed due to damage in a frontal crash. An estimated 3.5 percent of 

the drivers examined had a moderate or more severe lower leg injury from the floor or foot controls. An 

estimated 1.5 percent of the drivers examined had upper leg injuries from the instrument panel or knee 

bolster. Similarly the main independent variable, intrusion, also has a low estimated frequency of 

occurrence. An estimated 2 percent of the vehicles examined had floor or toe pan intrusion into the 

driver’s seating position, and an estimated 3 percent had instrument panel intrusion into the driver’s 

seating position. Given that these are small relative frequencies and that NASS-CDS is a statistical

sample with significant variation in the sample weights due to unequal probabilities of selection, it can be 

difficult to establish statistically significant relationships.

Even with these limitations, the overall results appear to support the basic hypothesis that more intrusion 

is likely to contribute to more leg injuries. Table 9 demonstrates that as the amount of floor and toe pan 

intrusion increases, the percent of drivers with lower leg injuries from the floor or foot controls also 

increases. Table 9 also demonstrates that the presence of instrument panel or knee bolster intrusion is 

associated with a higher percentage of drivers with upper leg injuries, but the relationship between the 

amount of intrusion and the risk of injury is less clear. At the same time, Table 10 shows that the change 

in velocity is associated with injury risk and should be considered when assessing the independent effect 

of intrusion. 

The multivariate models used to determine the independent effect of intrusion considered the possible 

effects of delta-V, age, gender, BMI, vehicle age, and vehicle body type as well as the results presented in 

other sections of the paper. More specifically, the following hypotheses were considered in the statistical 

models:

• Intrusion: Drivers in vehicles with higher amounts of intrusion are more likely to experience 

lower extremity injuries than drivers in vehicles with less intrusion.

• Delta-V: Drivers in frontal crashes with larger changes in velocity (delta-V) are more likely to 

experience lower extremity injuries than drivers in frontal crashes with smaller changes in 

velocity.

• Driver Age: Older drivers are more likely to experience lower extremity injuries than younger 

drivers.

• Driver Gender: Women are more likely to experience lower extremity injuries than men. 

• Driver BMI: Drivers with higher BMIs are more likely to experience lower extremity injuries 

than those with lower BMIs. 

• Vehicle Age: Newer vehicles (those from model year 2003 and later) are likely to produce 

different injury patterns than older vehicles (model year 1998 through 2002).

• Vehicle Type: Light trucks and vans are likely to produce different injury patterns than passenger 

cars.

First, intrusion was examined as a continuous and a dichotomous indicator variable based upon the results 

in Table 9. Second, separate models were developed for full frontal and left offset/SOI damage to remove 

crashes that occur on the right side of vehicle. While none of the variables for driver and vehicle 

characteristics were statistically significant in all twelve models, the results generally supported the 

hypotheses regarding age, gender and BMI. However, the focus of this analysis is the role of intrusion, 
15

and the fact that most of the variables were statistically significant in some of the models suggests that 

they are important control variables for assessing the independent effect of intrusion. 

Overall, the results suggest that intrusion is correlated with lower extremity injuries even when 

controlling for delta-V. However, the results also indicate that the magnitude of the relationship is 

conditional on frontal damage type. Table 13 summarizes the results from the 12 logistic models by 

presenting the odds ratios associated with intrusion from each logistic regression model. 

Table 13: Summary of Odds Ratios for Intrusion and Injury

Drivers With/ Lower Leg Injury Drivers With Upper Leg Injury

Odds Ratio for 

Intrusion in cm

Odds Ratio for 

Intrusion Indicator

Odds Ratio for 

Intrusion in cm

Odds Ratio for 

Intrusion Indicator

All Frontals Not significant 2.02

(1.04, 3.92) Not significant 4.20(1.71, 10.33)

Full Frontal 1.14

(1.03, 1.26)

7.15

(1.02, 50.21)

1.05

(1.00, 1.10)

8.31

(4.05, 17.02)

Left Offset/SOI 1.05

(1.01, 1.10)

6.92

(2.38, 20.16)

1.04

(1.01, 1.08)

17.30

(4.25, 70.47)

Note: 95 percent confidence intervals in parentheses.

The logistic model for all frontals demonstrate that the presence of intrusion has a statistically significant 

positive effect on the odds ratio for both lower and upper leg injuries, but the continuous measure of the 

level of intrusion does not have a statistically significant result. As discussed above, it is likely that the 

model had an easier time determining that any intrusion is more likely to increase the risk of injury versus 

no intrusion than it is for the model to demonstrate that one additional centimeter of intrusion is more 

likely to increase the risk of injury.

The results also indicate that intrusion has a greater effect on the odds of injury when the analysis is 

constrained to full frontal and to left offset/SOI damage. This difference appears to be the result of 

removing right offset/SOI damage, which are on the far side of the vehicles with respect to the drivers. 

As seen in Tables 7 and 8, these crashes generally do not have intrusion into the drivers’ seating 

positions, and when intrusion does occur, it tends to be small in magnitude. Therefore, since these 

crashes have little to no intrusion, removing them from the statistical models reduces some of the 

background noise that was attenuating the estimated effect of intrusion. The result of removing them is 

that continuous intrusion is a statistically significant predictor of the risk of injury with full frontal and 

with left offset/SOI damage, and the estimated odds ratio for the indicator of the presence of intrusion 

increases in magnitude in full frontal and left side damage types compared to the model of all frontal 

crashes.

Table 13 also shows that the estimated odds ratios have very large confidence intervals. These large 

confidence intervals suggest why it is difficult to make statistically significant distinctions across different 

damage types such as whether the effect of intrusion has a larger magnitude under full frontal crashes 

than under left offset and SOI crashes. It also suggests that more data is needed to obtain more precise 

estimates of the effect of intrusion. However, even with these limitations, the overall findings support the 

hypothesis that intrusion increases the risk of lower extremity injuries.
16

References

Crandall, J., Martin, P., Bass, C., Pilkey, W., Dischinger, P., Burgess, A., O’Quinn, T., & Schmidhauser, 

C. (1996). Foot and Ankle Injury: The Roles of Driver Anthropometry, Footwear, and Pedal 

Controls. 40th Annual Proceedings of the Association for the Advancement of Automotive Medicine, 

pp. 1-18.

Crandall, J., Martin, P., Sieveka, E., Pilkey, W., Dischinger, P., Burgess, A., O’Quinn, T., &

Schmidhauser, C. (1998). Lower Limb Response and Injury in Frontal Crashes. Accident Analysis 

and Prevention 30(5):667-77.

Eigen, A., & Glassbrenner, D.. 2003. The relationship between occupant compartment deformation and 

occupant injury. (Report No. DOT HS 809 676). Washington, DC: National Highway Traffic Safety 

Administration.

Halloway, D., Saunders, J., Yoganandan, N., & Pintar, F. (2011). An Operational Definition of Small 

Overlap Impact for Published NASS Data. Society of Automotive Engineers (SAE) 2011 World 

Congress, paper number 2011-01-0543. Warrendale, PA: SAE International.

Kuppa, S., Wang, J., Haffner, M., & Eppinger, R. (2001). Lower Extremity Injuries and Associated 

Injury Criteria. 17th International Technical Conference on the Enhanced Safety of Vehicles, paper 

number 457.

Read, K., Kufera, J., Dischinger, P., Kerns, T. Ho, S., Burgess, A., & Burch, C. 2004. Life-Altering 

Outcomes after Lower Extremity Injury Sustained in Motor Vehicle Crashes. Journal of Trauma

57(4):815-23.

Rudd, R. (2009). Updated Analysis of Lower Extremity Injury Risk in Frontal Crashes in the United 

States. 21st International Technical Conference on the Enhanced Safety of Vehicles, paper number 

09-0556.
17

Appendix

Table 14: Detailed Lower and Upper Leg Injuries

Injury 

Severity

Weighted 

Estimate of 

Injuries at 

MAIS for 

Lower Leg

(Sample 

Size)

Weighted 

Estimate of 

Injuries at 

MAIS and 

From Floor 

or Foot 

Controls

(Sample 

Size)

Weighted 

Estimate of 

Drivers With 

Injury

(Sample Size)

Weighted 

Estimate of 

Injuries at 

MAIS for 

Upper Leg

(Sample 

Size)

Weighted 

Estimate of 

Injuries at 

MAIS and 

From 

Instrument 

Panel of 

Knee 

Bolster

(Sample 

Size)

Weighted 

Estimate of 

Drivers With 

Injury

(Sample Size)

AIS 2 

(Moderate)

132,131

(595)

127,458

(502)

91,625

(303)

35,286

(176)

33,421

(152)

31,031

(132)

AIS 3 

(Serious)

12,111

(173)

7,024

(97)

6,015

(88)

17,839

(253)

13,029

(200)

9,785

(145)

AIS 4 

(Severe)

172

(4)

135

(3)

135

(3)

AIS 5 

(Critical)

5

(1)

Injury Total 144,243

(768)

134,482

(599)

97,280

(391)

53,301

(434)

46,585

(355)

40,951

(280)

No AIS 2+ 2,656,637

(6,893)

2,712,966

(7,004)

Grand Total 2,753,917

(7,284)

2,753,917

(7,284)

Source: NASS-CDS 1997-2009

Table 15: Injuries by Frontal Damage Type

Frontal 

Damage Type

Drivers With Lower Leg Injuries 

From Floor or Foot Controls

Drivers With Upper Leg Injuries 

From Instrument Panel or Knee 

Bolster 

Sample Size

Weighted Percent of Cases With 

Moderate or More Severe Injuries

Weighted Percent of Cases With 

Moderate or More Severe Injuries

Center 6.0% 7.0% 358

Full Frontal 5.9% 1.3% 3,078

Left Offset 0.8% 1.1% 1,325

Left SOI 0.8% 1.0% 751

Right 

Offset/SOI10 2.6% 1.6% 1,772

Total 3.5% 1.5% 7,284

Source: NASS-CDS 1997-2009; weighted total = 2,753,917

Note: Modified Rao-Scott Chi-Squared Test, Pr >0.05 (lower leg), Pr >0.05 (upper leg)

 10 Right offset and SOI combined due to the small number of cases of intrusion in each category.
DOT HS 811 578 

March 2012

8468-031512-V1a