Injuries to Restrained Occupants in Far-Side Crashes

Abstract

Occupants exposed to far-side crashes are those seated on the side of the vehicle opposite the struck side. This study uses the NASS/CDS 1988–98 to determine distributions of AIS 3+ injuries among occupants exposed to far-side crashes and the sources of the injuries. The William Lehman Injury Research Center (WLIRC) data from 1994–98 is used to assess injury mechanisms among seriously injured crash exposed far-side occupants.

The NASS/CDS indicated that injury patterns for far-side restrained drivers were different from far-side restrained front passengers. For the driver, the head accounted for 40% of the AIS 3+ injuries in far-side collisions and the chest/abdomen accounted for 45.5%. For the right front passengers, head injuries contributed 27.2%, while chest and abdominal injuries accounted for 64.5%. The opposite-side interior was the most frequent contact associated with driver AIS 3+ injuries (30.5%). The seat belt was second, accounting for 22.6%. Among thirteen WLIRC cases of far-side belted occupants with MAIS 3+ injuries, five of the most serious injuries were attributed to the seat belt. The liver or the spleen was the most seriously injured body organ in all five cases.

The seat was the most frequent source of passenger AIS 3+ injuries for the NASS/CDS weighted cases. However, non-contacts, contacts with other occupants, and the seat belt contacts were more frequent sources when considering the raw number of injuries.

Overall, contacts with the opposite side of the car interior and with safety belts were the most frequent causes of AIS 3+ injuries in far-side crashes. The presence of an occupant on the near-side changed the injury pattern of the far-side occupant, mitigating injuries from contacts with the opposite side interior of the vehicle.

Test procedures required by present safety standards for side crashes require the crash dummies to be located on the side of the vehicle closest to the impact. Far-side occupants, those located on the side opposite the impact, are not included. Studies of injuries in far-side crashes may assist in identifying safety systems and test procedures to further improve occupant safety.

An objective of this study was to examine injury patterns for far-side front seat occupants in side collisions. A number of earlier studies have examined injuries to far-side occupants, but have not differentiated between the driver and the front passenger.

Mackay (1991) examined 193 crashes with belt restrained far-side occupants during the period 1983–1989. The 193 cases contained 150 AIS 2 injuries and 15 AIS 3+ injuries. Among those with AIS 2+ head injuries, 35% came out of the shoulder belt. For those with AIS 2+ abdominal injuries, 72% were from contact with the safety belt. Contact with the belt system was the most frequent source of chest injuries (59%).

Frampton (1998) studied 295 crashes with belt restrained far-side occupants between June 1992 and April 1996. These cases included 46 MAIS 2 and 33 MAIS 3+ injuries. The MAIS 2 median deltaV was 25 km/hr. The median MAIS 3+ deltaV was 35 km/hr. Frampton found that MAIS 2+ injury rates were higher in perpendicular crashes than in oblique crashes.

Thomas (1999) investigated a sample of 474 side crashes between 1992 and 1998. The cases contained 226 MAIS 3+ survivors, and 188 fatalities. Thirty-four percent of the MAIS 3+ survivors and 32% of the fatalities were seated on the non-struck side. The distribution of injuries by body region for the 21 MAIS 3+ survivors on the non-struck side and without interaction with other occupants were: Head – 52%; Neck – 14%; Thorax – 19%; Upper Extremity – 38%; Pelvis – 14%, and Lower Extremity 14%. For the fatalities the equivalent: Head – 68%; Neck – 18%; Thorax – 86%; Abdomen – 41%; Upper Extremity – 9%; Pelvis – 9%, and Lower Extremity 18%.

Fildes (1991) examined injuries sustained in side collisions by drivers in Australia. The study was based on the Monash University crashed vehicle file consisting of 227 vehicles and 267 patients from crashes that occurred in Victoria during 1989 and 1990. The file contained 572 variables to describe the crash and the occupant. Fildes found that the injury rate of AIS 2+ head injuries was twice as high in far-side impacts as in near-side impacts. In far-side impacts, head and chest injury rates were about equal. The four most frequent sources of injuries were the instrument panel, the roof, the door panel, and the other occupant. The injury rate due to seat belts was about half that of the four most frequent sources.

METHODOLOGY AND DATABASES

In this study, National Automotive Sampling System/Crashworthiness Data System (NASS/CDS) for the years 1988 to 1998 was used to examine the distribution of injuries and injuring contacts for belted occupants in far-side impacts. Data from the William Lehman Injury Research Center (WLIRC) at the University of Miami School of Medicine was used to examine injury modes for belted occupants in far-side crashes. Belted occupants include those with three point belts, as well as those with two point belts.

The National Highway Traffic Safety Administration (NHTSA) maintains the NASS/CDS database of vehicle crashes in the United States. The NASS/CDS is a stratified sample of light vehicles involved in highway crashes that were reported by the police and involved sufficient damage that one vehicle was towed from the crash scene. The database was compiled between 1988 and 1998 and has been used extensively by NHTSA and others to assess the effectiveness of safety systems in reducing casualties in the crashes that occur on US highways.

The WLIRC database provides in-depth crash and injury information on the most severely injured motor vehicle occupants in Miami-Dade County, Florida. Since 1995, the WLIRC has investigated 92 side impact collisions. In each case, the occupant was either transported to the Ryder Trauma Center (RTC) at the University of Miami/Jackson Memorial Medical Center, or, if dead at the scene, directly to the Dade County Medical Examiner’s Office. Detailed data has been collected from the crash scene, the damaged vehicle, and the injured occupant.

The criteria for admission into the WLIRC side impact study is as follows: (1) the subject must have been involved in a side collision, (2) the subject must not have been completely ejected from the vehicle, (3) the subject must have met trauma triage criteria and (4) the subject must sign a written consent to participate. Criteria (3) and (4) do not apply in medical examiner cases. Subject screening is 100% of all occupants involved in side collisions arriving at either the Ryder Trauma Center or the Dade County Medical Examiner’s office. Less than 10% of the subjects who met study criteria refused to participate. The WLIRC database represents a near census of severely injured motor vehicle occupants in Dade County.

In the 1995–1998 WLIRC data, twenty-three occupants were in far-side collisions. Nine were restrained by three point belts, four were restrained by two point belts, and ten were unrestrained. This study examined injuries to the thirteen occupants with two or three point belts.

INJURIES IN FAR-SIDE CRASHES BASED ON NASS/CDS

In the NASS/CDS data query, far-side occupants were defined as drivers in vehicles with right side damage and principal direction of force in the 1 to 5 o’clock direction or right front passengers in vehicles with left side damage and principal direction of force in the 7 to 11 o’clock direction.

In addition, the following restrictions were imposed: belted occupants only, age 16 or older, and no subsequent rollover of the struck vehicle. The data set contained 4696 cases – 3576 drivers and 1120 right front passengers. Of this driver population, 235 drivers had serious (MAIS 3 or greater) injuries with an aggregate of 653 AIS 3+ injuries. Of the right front passengers, 52 had serious injuries, with 123 injuries of AIS 3 or greater. All but 2 of the seriously injured occupants were restrained by 3-point belts.

Each NASS/CDS case contains a weighting factor that is used by the NHTSA to extrapolate the individual cases to the national numbers. The distributions to follow are based on the NASS/CDS weighted events. The application of weighting factors produced 64,142 AIS 3+ injuries. Drivers sustained 84% of the raw AIS 3+ injuries and 87.6% of the weighted AIS 3+ injuries.

Table 1 shows the AIS 3 and greater injury distribution by body region for belted drivers and right front passengers in far-side crashes. All skull, brain and facial injuries are classified as head injuries. Injuries to the chest and abdomen are classified as trunk injuries. Injuries to the pelvis are classified as lower extremity injuries and shoulder injuries are included in the upper extremity category. For the drivers, head injuries account for 40% of the AIS 3+ injuries and trunk injuries account for 45.5%. In contrast, for right front passengers, head injuries account for 27% of the AIS 3+ injuries and trunk injuries for 64.5%. Chest/abdominal injuries dominate the severe injuries to far-side belted right front passengers.

Table 1.

AIS 3+ Injury Distribution for Belted Front Seat Occupants in Far-Side Crashes by Body Region, NASS/CDS 1988–1998

Body Region	All	Drivers	RF Passengers
	Percent	Percent	Percent
Head	38.2	40.0	27.2
Trunk	48.0	45.5	64.5
Spine	2.2	2.5	0.0
Lower Extremity	5.9	6.2	3.3
Upper Extremity	5.6	5.7	5.1

An examination of the contacts that cause the injuries in far-side crashes provides insight into the difference between the injury mechanisms of drivers vs. right front passengers. Table 2 shows the distribution of AIS 3+ injuries by injuring contact. Table 3 shows the AIS 3+ injury distribution by body region and injuring contact. Body regions and contacts that constituted less than 2% of the AIS 3+ injuries were not included in Table 3. In Tables 2 and 3, the Side Interior category includes all interior side surfaces of the vehicle above the floor and below the roof.

Table 2.

AIS 3+ Injury Distribution for Belted Front Occupants in Far-Side Crashes by Injuring Contact, NASS/CDS 1988–1998

Injuring Contact	All	Drivers	RF Passengers
	Percent	Percent	Percent
Seat Belt	20.8	22.6	8.5
Dashboard	5.2	4.3	11.4
Steering System	2.4	2.4	2.5
Left Side Interior	7.2	8.0	1.7
Right Side Interior	26.7	30.5
Non Contact	6.4	6.0	9.0
Other Occupant	2.9	1.4	13.2
Roof	12.2	13.1	5.9
Seat	7.5	3.5	35.4
All Other	8.7	8.2	12.4

Table 3.

AIS 3+ Injury Distribution for Belted Front Occupants in Far-Side Crashes by Body Region and Injuring Contact, NASS/CDS 1988–1998

Body Region	Injuring Contact	All	Drivers	RF Passenger
		Percent	Percent	Percent
Trunk	Belt	20.6	22.3	8.5
Trunk	Right Side Interior	11.8	13.5
Head	Right Side Interior	11.4	13.1
Head	Roof	10.2	10.8	5.9
Head	Left Side Interior	6.1	6.8	1.5
Trunk	Seat	5.4	2.7	23.9
Trunk	Other Occupant	2.3	1.2	10.4
Trunk	Non Contact	2.2	1.9	4.5
Head	Non Contact	2.1	2.1	1.9
Head	Seat	2.1	0.8	11.5
Spine	Roof	2.0	2.3
Head	Dash	1.9	2.2	0.3
Trunk	Dash	1.6	0.5	9.0
Head	Other Occupant	0.5	0.2	2.8

For the driver, the Side Interior and the Seat Belt are the most frequent sources of injury. For the right front passenger, the presence of the driver greatly reduces the injuries attributed to the seat belt and the side interior. Instead, the seat and the other occupant (driver) are the most frequent injury sources.

Table 3 provides additional insights into injury mechanisms. For the driver, AIS 3+ injuries from contact with the Opposite Side Interior are primarily head and trunk injuries and they are about equally distributed. The Seat Belt to trunk contact accounts for virtually all AIS 3+ Seat Belt contact injuries. The right front passenger AIS 3+ injuries from contacts with the Seat Belt and Opposite Side Interior are much less than for the driver.

Table 4 shows the raw numbers of AIS 3+ injuries for belted far-side drivers and right front passengers in NASS/CDS 1988–1998. In addition, the total numbers of AIS 3+ injuries, and of MAIS 3+ injured occupants are shown. The last two columns in Table 5 show the average NASS weighting factors associated with the contacts.

Table 4.

Raw Numbers and Average Weight of AIS 3+ Injuries for Belted Front Occupants in Far-Side Crashes by Injuring Contact, NASS/CDS 1988–1998

Injuring Contact	Drivers	RF Passengers	Drivers	RF Passengers
	Number	Number	Avg. Weight	Avg. Weight
Seat Belt	61	14	208	48
Dashboard	45	10	53	91
Steering System	24	3	57	65
Left Side Interior	39	6	116	23
Right Side Interior	239	-	72	-
Non Contact	64	24	54	30
Other Occupant	32	26	25	40
Roof	46	11	160	42
Seat	30	13	66	216
All Other	73	17	62	59
Raw N (AIS)	653	124	86	64
Raw N (MAIS)	235	52	123	77

Table 5.

Occupant & Vehicle Characteristics in Far-side Crashes – WLIRC Data

Number	Age	Height	Sex	Wgt.	Crush	Lat Dv	CV	POV	Position
98-005S	37	1.60	F	56.7	.16	10.4	SC	Car	Driver
97-020KL	56	1.63	F	77.1	.37	11.4	SC	PU	Driver
98-006BL	77	1.73	M	123.0	.25	12.5	LC	Car	Driver
96-020EL	21	1.55	F	61.2	.30	12.8	MC	Car	Driver
96-041JL	27	1.60	F	58.1	.15	12.8	SC	PU	Driver
97-044FL	62	1.68	F	56.7	.25	15.4	SC	PU	RF Pass
98-025AL	12	1.65	F	70.8	.13	18.5	LC	Car	LR Pass
94-L016J	66	1.78	M	75.3	.46	39.5	MC	PU	Driver
98-011S	49	1.42	F	52.2	.71	48.0	SC	PU	RF Pass
97-019S	21	1.73	M	64.4	1+	49.8	SC	Pole	Driver
98-004S	47	1.63	F	99.8	1+	72.2	SC	PU	Driver
97-038S	16	1.80	M	85.7	1+	71.8	SC	Pole	RF Pass
98-009SD	18	1.80	M	60.3	1+	74.0	SC	Pole	Driver

Driver contacts with the Opposite Side Interior constitute about 37% of the raw AIS 3+ driver injuries and carry a weight close to the average. Seat Belt contacts constitute about 9% of the driver injuries and carry a weight more than twice the average.

For the passenger, Non-contact and Other Occupant contacts account for about 40% of the raw AIS 3+ injuries, but carry low weighting factors. The Seat accounts for 10.5% of the raw injuries but carries a high weighting factor.

Both the raw data and the filtered data indicate that contacts with the Opposite Side Interior by the passenger are greatly reduced by the presence of the driver.

INJURIES IN FAR-SIDE CRASHES BASED ON WLIRC DATA

The William Lehman Injury Research Center collects data elements that are similar to NASS/CDS, but with additional crash and injury documentation. Crash severity (delta-V) is determined in the same way as in NASS/CDS. Both systems use an algorithm named SMASH that calculates the delta-V, based on the mass, stiffness, and deformation of the two colliding vehicles.

The WLIRC data set contained 92 cases of occupants in side impact crashes. Twenty-three of these cases involved far-side occupants, and thirteen cases were belted far-side occupants. All thirteen cases had AIS 3+ injuries. The characteristics of these cases are summarized in Tables 5 and 6. Table 5 lists the Age, Height (meters), Sex, and Weight (kilograms) of the injured far-side occupants. The maximum Crush (meters) and the Lateral Delta-V (kilometers per hour) are listed, also. The maximum Crush is the maximum deformation of the exterior of the struck vehicle side. It is an indicator of the crash severity and the extent of occupant compartment intrusion. The columns labeled CV and POV indicate the Case Vehicle (CV) and Principal Other Vehicle or object (POV). The abbreviations are as follows: SC – small car; MC- medium car; LC – large car; and PU – pickup or other light truck. The Occupant Position is listed in the final column. The RF abbreviation is right front and LR is left rear.

Table 6.

Injury Characteristics in Far-side Crashes – WLIRC Data

Number	Rest.	Occ Loc	MAIS	Fatal	Max Injury	Contact
98-005S	L&S	Left	3	No	Cervical cord	Non-contact
97-020KL	L&S	Left	5	No	Brain	R Inst. Panel
98-006BL	L&S	Left	4	Yes	Brain	Pass. Air Bag
96-020EL	S	Left	4	No	Liver	Belt
96-041JL	S	Left	3	No	Liver	Belt
97-044FL	L&S	Right	3	No	Spleen	Belt
98-025AL	L&S	Left	5	Yes	Liver	Belt
94-L016J	L&S	Left	5	Yes	Brain	R Side Interior
98-011S	L&S	Right	5	Yes	Brain	Unknown
97-019S	L&S	Left	5	Yes	Brain	Other Vehicle
98-004S	S	Left	4	No	Liver/Spleen	Belt
97-038S	L&S	Right	5	Yes	Brain	L Side Interior
98-009SD	L&S	Left	6	Yes	Aorta	R Side Interior

Table 6 lists the crash case Number, the type of Restraint, Occupant Location (side of the car), the Maximum AIS, an indication if the outcome was Fatal, the organ with the Maximum Injury, and the Contact identified with the Maximum Injury. The abbreviation S indicates shoulder belt only. The L&S indicates a 3-point lap and shoulder belt.

For the thirteen WLIRC cases, the median lateral delta V was 18 km/hr. The median values for the occupants were as follows: age – 37; height – 1.64 meters; weight – 64.4 kg. Nine of the occupants were in small cars. Six of the POV’s were pickup trucks, and three were narrow fixed objects.

Belt contact was the most frequent injuring contact in the lower severity far-side crashes in the WLIRC data. Seven of the thirteen cases had a lateral delta-V of 19 km/hr or less. For these seven less severe cases, the belt or air bag was responsible for five of the most serious injuries. Belt contact injuries were present four of the cases, two of which were 2-point shoulder belts without the lap belt fastened. In all belt injury cases, the most severely injured organs were the liver or the spleen.

DISCUSSION

The NASS/CDS data for belted front seat occupants indicates that the seat belt accounts for 20.8% of AIS 3+ injuries in far-side crashes. For WLRIC data, about 38% of the MAIS 3+ injuries were belt induced. Most of these belt injuries occurred in the lowest severity crashes with lateral delta-V less than 19 km/hr. Earlier studies by Mackay found that 59% of AIS 2+ chest injuries and 72% of abdominal injuries among belt restrained far-side occupants were from seat belt contacts (Mackay, 1991). The NASS/CDS data sample is stratified in such a way that low severity crashes are sampled at a much lower rate than the higher severity crashes. The belt contacts for the driver carry a large average weighting factor, suggesting a smaller than average sample of cases. The NASS/CDS sample may not be sufficiently robust to adequately capture injury modes in the lower speed ranges.

The NASS/CDS indicated that the largest source of injury to belted drivers in far-side impacts was the Opposite Side Interior. For the weighted data the Opposite Side Interior percentage was 30.5% and for the raw data it was 36.6%. Inaccuracy of belt use reporting in NASS/CDS may result in these percentages being inflated. However, the Opposite Side Interior contacts constituted about 23% of the WLRIC MAIS 3+ injuries in far-side crashes where belt reporting was verified. Fildes reported the door panel as one of the most frequent injury contacts for Australian far-side AIS 2+ injuries (Fildes, 1991). Mackay reported that the far-side occupant came out of the belt in 35% of the cases with AIS 2+ head injuries (Mackay, 1991). These studies suggest that opportunities exist for improving the occupant retention and chest/abdominal loading of safety belts in far-side crashes.

The NASS/CDS indicated that the injuring contacts for the passenger were different from the driver. The 100% presence of the driver provided a mitigating contact for the right front passenger in far-side impacts. As a consequence, fewer passenger contacts were with the opposite side.

The raw data for right front passengers indicated that injury contacts were from a large number of sources. The seat was the most frequent source of passenger AIS 3+ injuries when the NASS/CDS weighting factors were applied. However, contacts with other occupants, non-contacts, and contacts with the seat belt were more frequent when considering the raw number of injuries.

CONCLUSIONS

Based on NASS/CDS 1988–1998, belted drivers and passengers have different injury modes in far-side crashes. Head injuries are more prevalent in belted drivers than in belted passengers, representing 40% of the AIS 3+ injuries for drivers, but only 27% for passengers. For belted right front passengers, chest/abdominal injuries account for about 65% of the AIS 3+ injuries compared to 45.5% for drivers.

For belted drivers in far-side crashes, the most harmful injury source is the opposite side of the car (30.5%). The second most harmful injury source is the seat belt (22.6%). Five of thirteen belted far-side occupants in the WLIRC data had MAIS 3+ injuries from belt contacts. In all belt contact cases, the most seriously injured organ was the liver or spleen.

The presence of an occupant on the near-side changes the injury pattern of the far-side occupant, mitigating injuries from contacts with the opposite side interior. Crash testing to evaluate safety features to mitigate contacts with the opposite side interior should be done without a near-side dummy.

(Presenter: Kennerly Digges)

John Treat: In the last case that you showed, I wonder if you have an opinion as to whether the shoulder belt portion of the left rear restraint, in addition to being ineffective, may have played some role in adding to the internal loading and injury and in the movement of the lap belt?

K. Digges: Yes, we think it may have pulled the lap belt up and pulled it up on the soft tissue and as a consequence -- she was a relatively stocky girl with a lot of soft tissue to be injured.

Don Huelke: In your early slides, you talked about the raw data and showed the different areas that were injured. Were these all AIS levels?

K. Digges: They were only AIS 3+.

D. Huelke: In one of the early slides, I did a quick calculation. Non-contact injuries were 10–20%. How can you get an AIS 3 injury from non-contact?

K. Digges: I think those are probably the ones they didn’t know what they were so coded them as non-contact. Frequently, when you don’t know what it is, it’s coded as non-contact in NASS.

D. Huelke: I disagree with one of your conclusions in one of the cases you presented. You said that the seat belt was ineffective in far side crashes.

K. Digges: I said the shoulder belt, not the seat belt.

D. Huelke: And you showed the dummy movement. That’s true in a 90° impacts, but those are relatively rare, and a far side impact is anywhere from the front headlight to the taillight. And if you get a vehicle spinning, you get a lot of effectiveness of the shoulder belt. In a pure 90° T-bone, I think you’re correct, but I think we have to make that distinction.

K. Digges: It would be nice to have some test data. There is virtually no test data to support that one way or the other, unfortunately.

Joe Marsh: I commend you for looking at both raw and the weighted numbers. That’s what I was trying to get at before. A good guideline for reviewing papers in the future is that both are looked at. I have a question which is a little tangential. Oftentimes if you’re looking at near side impacts, the delta V is less of interest. It’s more the closing velocity or the impact velocity, that sort of thing, that is related to the injury mechanism. I hadn’t really thought about it in the far side impact. Any comment as to which measure is more related to injury?

K. Digges: I don’t use it [ΔV] much in NASS. When I use it in NASS, I have to throw out too many cases, and when I see it, I don’t believe it. I’m not sure how valuable the delta V is in side impacts and therefore I’ve resorted to using the weighting factors as a surrogate for saying whether these are occurring in low and high speed severity. Or we can start looking at extent of damage.

J. Marsh: I was thinking in the sense of your understanding the mechanics of the crash and the injury mechanisms. In a near side impact, it’s closing velocity that’s more related to injury than delta V, but in far side crashes, if you had both measures, which would you be happier having?

K. Digges: I think that we are seeing belt injuries at relatively low delta Vs and as a consequence of that, I don’t think the delta V is nearly as important in far side impacts. In near side impacts I think the violence is much more closely related to delta V. In far side impacts, as Dr. Huelke says, it may be much more related to the nature of the crash direction or the vector. There are other things than delta V in far side impacts. In the very severe impacts, you get opposite side head injuries, but in those moderate range impacts where we can really try to do something, I think the crash direction and so forth is more important than delta V.

Greg Stephens: Joe brings up a good point. As it relates to delta V, it’s more a measure of a specific delta V. In other words, you’re depicting a severity level at the center of gravity of the vehicle when rotation factors may end up doubling the specific delta V, let’s say, at that left rear seating position. Would you care to comment on that for your last case?

K. Digges: I think your point is well taken. We have not gone the second mile to try and develop an alternative to delta V. We use the delta V that NASS uses and have lived with it because it allows you to make this data agree with the NASS data. However, as I speak right now, I have a grad student doing exactly what you’re talking about. We are reconstructing and attempting to look at a better delta V surrogate.