Elias, 1

LARGE SCHOOL BUS SAFETY RESTRAINT EVALUATION - PHASE II

Jeffrey C. EliasTransportation Research Center, Inc.Lisa K. Sullivan, VRTCLinda B. McCray, AVSRNational Highway Traffic Safety AdministrationUnites StatesPaper No. 313

ABSTRACT

This paper details the National Highway TrafficSafety Administration’s (NHTSA) continuingresearch and testing activities on large school bussafety restraints. This paper will discuss relativeperformance of compartmentalization, lap beltrestraints and lap/shoulder belt restraints, as well asthe effects of seat back height and seat spacing on theperformance of these safety restraint strategies.Results of NHTSA’s frontal sled testing efforts withan inflatable airbag belt system are reviewed. Theagency’s efforts on researching side impactprotection are also briefly discussed. This papersupplements the results presented in the 17th

Enhanced Safety of Vehicles Conference (ESV),Paper No. 345, “Large School Bus SafetyEvaluation” [1], and discusses results for tests thatwere conducted subsequent to the publication of thatpaper.

INTRODUCTION

As discussed in 17th ESV Paper No. 345 [1],NHTSA’s school bus safety restraint researchprogram consisted of three phases: (1) defining theextent of the problem, (2) conduct of both a frontaland side impact full-scale dynamic crash test withlarge school buses, and (3) conduct of a series of sledtests to evaluate various school bus restraintalternatives. This paper will only discuss the resultsfrom Phase 3: sled test evaluation ofcompartmentalization, lap belts, laps/shoulder beltsand inflatable airbag belt restraints. Phases 1 and 2are discussed in the 17th ESV paper.

PHASE III-SLED TESTING AND VALIDATION

Figure 1 is a plot overlay showing the deccelerationpulse of the vehicle’s center of gravity (CG)accelerometer from the frontal rigid barrier crash testwith an acceleration plot of a sled test simulation ofthe crash. As can be seen, the sled’s accelerationpulse is a good replication of the acceleration timehistory of the full-scale frontal impact test. The

leveling off of the acceleration pulse of the crash testfrom about 40-90 ms is a result of the bus bodysliding along the chassis. The somewhat higheracceleration profile of the sled during this timeresulted in a slightly higher velocity change (delta-v)for the sled tests when compared to the crash test.

Figure 1. Crash Test and Sled Test Pulses.

Over the course of testing, two different sled buckswere used to evaluate the various bus safety restraintsystems. The first sled buck was fabricated from asection of a bus body. This allowed assessment ofthe degree of deformation/energy absorption by thebus floor and the potential for occupant interactionwith any portion of the bus interior other than theseats. Figure 2 is a photograph of this sled buck.The body section contained three rows of seats, withseats mounted on both the right and left side of thecenter aisle, which allowed for testing a potentialmaximum of 2 rows (or 4 seats) per test.

Testing with this sled buck showed that there was nosignificant interaction between the dummies and theinterior walls or ceiling of the bus in a full frontalcrash. There was incremental deformation to thefloor of the bus shell with repeated testing, but theamount of deformation was minimal for any singletest. The amount of impact energy associated withthis deformation of the bus floor was an insignificantportion of the total absorbed by the seat.

Elias, 2

Figure 2 - First (Full Shell) Sled Buck.

The second sled buck utilized a rigid floor of 1.3 cm(0.5 in) thick aluminum plate with an open frameconstruction. Figure 3 is a photograph of themodified sled buck used in subsequent sled tests.This design provided for a more durable, and thus amore consistent, test platform. It also allowed forbetter mounting of the high speed digital imaginghardware, resulting in more complete analysis of thedummies kinematics and their interaction with theseats and safety restraint systems.

Figure 3 - Second (Open Frame) Sled Buck

Sled Test Parameters

The initial test matrix was designed to focus on threetest parameters for evaluation:

1. Occupant size2. Restraint strategies3. Loading conditions (from unrestrained

occupants)

This matrix was subsequently expanded to assess theadditional factors of:

4. Seat spacing

5. Seat back height

Three occupant sizes were used to evaluate thevarious restraint strategies:

1. Average 6-year-old: represented by theHybrid III 6-year-old dummy at 114 cm /23.6 kg (44.9 in / 52 lb) with seated heightof 63.5 cm (25.0”).

2. Average 12-year-old: represented by theHybrid III 5th percentile female dummy at150 cm / 49 kg (59 in / 108 lb), with seatedheight of 78.7 cm (31.0”).

3. Large high school student: represented bythe Hybrid III 50th percentile adult maledummy at 175 cm / 78 kg (69 in / 172 lb)with seated height of 88.4 cm (34.8”).

Three different restraint strategies were initiallyevaluated using this test matrix. Late in the testingprogram, two additional restraint systems becameavailable for evaluation. These additional restraintsystems were subjected to an abbreviated test matrixcomparable to the first three restraint systems. Theinitial restraint systems were:

1. Compartmentalization2. Lap belt (with compartmentalization)3. Lap/shoulder belts on a bus seat with

modified seatbackThe two additional restraint systems were:

1. Lap/shoulder belt with compliant seat back2. Inflatable airbag lap belt

Three different loading conditions were simulatedduring the sled testing:

1. Restrained occupants (with no loading fromoccupants seated behind them)

2. Restrained occupants with rear loading(from unrestrained occupants seated behindthem)

3. Unrestrained occupants (into the seat-backpositioned in front of them).

Testing was conducted using three different seatspacings. The seat spacing was determined bymeasuring from the H-point1 of the SAE 3-dimensional machine (OSCAR) to the back of theseat (measured at the same vertical height of the H-point) located in front of the dummy. The seatspacing values selected for these tests were 48 cm

1 Mechanically hinged hip point simulating the actualpivot center of the human torso and thigh

Elias, 3

(19 in), 56 cm (22 in), and 61 cm (24 in). Thesevalues were selected based on information obtainedfrom the FMVSS 222 compliance tests. Review ofthese data showed seat spacing ranging from 41 cm(16 in) to 61 cm (24 in), with most falling between 48cm and 56 cm (19 in and 22 in). FMVSS 222 allowsa maximum seat spacing of 61 cm (24 in), while 48cm (19in) was found to be the practical minimum fornormal seating of a Hybrid III 50th percentile adultmale dummy. The third seat spacing of 56 cm (22 in)effectively spanned the most common range of seatspacing observed in the available data.

The current minimum seat back height required underFMVSS No. 222 is 50.8 cm (20 in) from the seatingreference point (SRP)2. A seat design option offeredby seat manufacturers, and required in several states,is a “high back” design where the seat back height istypically 61 cm (24 in) above the SRP. The higherseat back design was a necessity for the lap/shoulderbelt strategies tested, in order to provide an anchorpoint for the shoulder belt portion of the restraintsystems. In addition to the lap/shoulder belt seatdesigns, a number of standard seats with the “highback” option were obtained from BlueBird and theC.E.White Co. and included in the test program.

Injury and Kinematics Evaluation

The motion of the occupant in the seat, and itsinteraction with the seat back and seat restraints, areimportant factors in determining the type,mechanism, and potential severity of any resultinginjury. Analysis of the dummy kinematics was usefulin evaluating a restraint system’s performance anddetermining its potential for preventing, or causing,injury.

In addition to dummy kinematics, various injuryassessment criteria were used to assess the restraintsystems. All of these criteria were calculated asspecified in the Interim Final Rule for FMVSS 208“Occupant Protection.” The neck injury criterion,Nij, is calculated from moment and axial loads on theneck in a frontal impact. The criterion value isnormalized to a pass/fail value of 1.0, whichrepresents a 22 percent risk of serious neck injury.HIC15 is a 15 ms acceleration based criterion used toassess the risk of head injury. The pass/fail thresholdlimit of 700 represents a 30 percent risk of serioushead injury. Finally, the Chest G is based on a 3 ms

2 Manufacturer’s design reference point simulatingthe position of the center of pivot of the human torsoand thigh.

duration resultant acceleration with a pass/failcriterion threshold limit of 60 g’s, which represents a20 percent risk of serious chest injury.

Compartmentalization - Figure 4 is a plot of theresultant head accelerations (used to calculate HIC15)of a compartmentalized seat test for a 6-year-old and5th percentile adult female dummy. Figure 5 is a plotof the neck injury criterion (Nij) for the same test.

Figure 4 - Resultant Head Acceleration

Figure 5 – Neck Injury Criterion (Nij)

Figures 6, 7, 8 and 9 illustrate the typical sequence ofevents that occur in a frontal crash for a passenger ina compartmentalized seat. For this particular test,seat spacing was 48 cm (19 in) with impact into ahigh back seat design configuration. No dummieswere seated rearward of subject occupants.

The dummies were initially seated in a normal,upright position on the seat bench with the back ofeach dummy situated against the seat back (seeFigure 6). The dummies were positioned laterally bydesignating the seat as having outboard (wall side)and inboard (aisle side) seating positions andcentering the dummy on the corresponding side.

During the initial moments of the crash, the dummiesslid forward on the seat while maintaining theirupright posture. This continued until the lowerextremities or knees struck the seat back in front ofthe seated dummy (See Figure 7).

Elias, 4

Figure 6. Compartmentalization at 0 ms.

Figure 7. Compartmentalization at 100 msec.

Figure 8. Compartmentalization at 150 ms.

Figure 9. Compartmentalization at 210 msec.

At this point, the torso rotated forward and downwardcausing the head to strike the seat back. The 5th

percentile female showed a peak head acceleration atapproximately 110 ms, with the 6-year-old strikingshortly later in the event with a peak accelerationoccurring around 123 ms. These accelerationsgenerated HIC15 values of 207 and 250, respectively.

As the torso continued to rotate forward, the headwas forced rearward by the seat back placing amoment load on the neck. Figure 8 is an image takenat 150 ms into the crash event. The shoulders of bothdummies had come into contact with the seat back.This limited the degree of extension, and to someextent, the amount of loading placed on the neck.

As the dummies continued to slide forward on theseat bench, the upper torso continued to flatten outagainst the seat back, thereby reducing loading on theneck. By 210 ms (Figure 9) the chest had come intofull contact with the seat back, relieving the load onthe neck and allowing the Nij values to drop.

Lap Belt Restraints - The lap belted dummy had aninitial motion similar to that of thecompartmentalized restrained dummy. The dummybegan its motion by sliding forward on the seat benchuntil the slack in the restraint system was taken up.At this point, the pelvic region was restrained whilethe head and torso continued forward and rotateddownward into the seat back situated in front of thedummy.

Elias, 5

Figures 10 and 11 show the resultant headaccelerations and Nij plots of the dummy in lap beltrestraint system. The initial head impact (148 ms)produced a load on the neck of the 6-year-olddummy. The dummy kinematics and resulting neckand head injury values were similar to those seen inthe compartmentalization tests. However, as theupper body continued to pivot at the hips and rotateforward and down into the seat back, subsequentloading on the neck occurred. This can be seen as asecond peak in the Nij values that occurred well afterthe initial head impact (at approximately 175 ms).

Figure 10. Resultant Head Acceleration for LapBelt Restraint.

Figure 11. Neck Injury Criterion (Nij) for LapBelt Restraint.

By contrast, the neck loading for the 5th percentilefemale dummy at the point of head impact wasrelatively low. As the torso continued to rotateforward, the loading on the neck became muchhigher. Figure 12 is an image taken 150 ms into thetest. The relative degree of extension can beobserved for the two dummies. Interaction of thechest and shoulders with the seat back was restrictedby the lap belt. As the torso rotated forward, theenergy of this momentum was absorbed by the neckas it was forced into extension, rather than by impactof the chest and shoulders into the seat back. Underthese kinematic conditions, the 6-year-old dummywas subjected to a significant neck load, while the 5th

percentile female dummy was subjected to a muchhigher neck loading by the same torso rotation.

Figure 12. Lap Belt Restraint System at 150 ms.

The Nij response for a dummy using a lap beltrestraint system appears to be sensitive to the motionand orientation of the dummy’s torso, which in turnis affected by dummy stature and seat spacing. Sincethe upper body is not restrained or prevented by thelap belt from fully interacting with the seat back, it ispossible for an extreme degree of neck loading tooccur.

Lap/Shoulder Belt Restraint - The seat backstructures were modified to accommodate theadditional loading on the seat back due to occupant(s)loading the shoulder belt upper anchorage points forboth the production school bus seats manufactured byBus Belt and a prototype seat design developed bythe C.E.White Co. These designs still allow the seatback to deflect within the force deflection corridorspecified in FMVSS 222. At a pre-determined pointin the deflection range the seat back becomesstructurally more rigid, limiting the degree of totaldeflection and maintaining the compartmentalizedfrontal barrier (for occupants rear of the lap/shoulderbelt outfitted seat). Lap/shoulder belt systemsrestrain the upper body, preventing or significantlyreducing the velocity of head impact into the seatback, which in turn reduces moment loading on theneck and significantly reduces the neck injurycriterion (Nij) values.

The lap/shoulder belt restraint systems are sometimesmisused. Two common misuse scenarios that occurwere tested during this program: “misuse 1” –shoulder belt portion of the system placed behind theback of the dummy, and “misuse 2” – shoulder beltportion of the system placed under the dummy’s arm.With the belt placed behind the back (misuse 1), therestraint system essentially became a lap belt systemwith test results very similar to those observed withthe lap belt systems. When the shoulder belt was

Elias, 6

positioned under the arm (misuse 2), the shoulder beltcrossed low across the torso of the dummy whichtended to rotate the upper body of the dummy beforeimpact into the seat back This torso rotation tendedto confound the Nij results, which are correlated tomeasure a pure frontal loading condition.

Figure 13 is an image taken at the peak Nij loading,168 ms into the event, showing the neck at itsmaximum flexion. The maximum injury criteriavalues for this type of restraint, when correctly worn,typically occurred when the upper torso was stoppedby the shoulder restraint and the head and neck weresnapped forward from the inertial energy. Theresulting head accelerations and neck loadings wererelatively low with this type of restraint.

Figure 13. C.E.White Lap/Shoulder BeltRestraint System at 168 ms.

A potential issue raised by the installation oflap/shoulder belt restraint systems is the additionalloading that is placed on the seat back by theshoulder anchor portion of the restraint system. Theinertial loading due to the torso of a restrainedpassenger can increase the amount of forwarddeflection of the seat back, significantly reducing itsability to safely restrain (via compartmentalization)an unbelted passenger seated behind a lap/shoulderbelt restrained passenger. Current regulations requirethat safety restraint systems maintain the ability toprovide passive protection or restraint(compartmentalization in bus seat design) to thevehicle’s occupants. Increasing the structuralstrength of the seat back can address this problem,but the additional rigidity of the seat back maypresent a potential risk of increased injury to the“unrestrained” passenger. This could be particularlysignificant if the seat forward of the passenger isunoccupied since the seat back, with no additionaltorso loading to help deflect the seat back upon

impact, may be overly rigid for effective passiveprotection.

Initial sled tests indicated that the stiffer seat backs ofthese designs could increase the HIC15 injurycriterion significantly for the unbelted passenger.The C.E.White Co. provided a second prototype seatdesign with modified foam padding in the seat backthat significantly lowered the HIC15 values insubsequent testing. A second lap/shoulder beltdesign strategy to address this seat back issue wasdeveloped by Indiana Mills Manufacturing Inc.(IMMI). This seat design isolated the shoulder beltanchor points from the seat back by creating asecond, or “inner”, frame used to anchor the restraintsystem. Figure 14 is an image of a sled test of theIMMI seat. The inner seat back frame can be seen inthis image as it was pulled away from the “outer”frame of the seat back by the torso loading of therestrained dummies, as it is designed to do. The“outer” frame remained in position to provide apadded impact surface for the two unbelted 50th

percentile adult male dummies seated behind therestrained dummies in this test.

Figure 14. IMMI Lap/Shoulder Belt RestraintSystem.

Lap Belt Air Bag Restraint - A final safety restraintdesign tested in this program was developed byAMSAFE. The restraint, which was originallydeveloped for use in commercial passenger aircrafts,utilizes an airbag system incorporated into a lap beltrestraint. Figure 15 is an image taken at 50 msshowing the initial deployment from the lap belt.The airbag expands outward from the passenger’s lapinto the space between the passenger and the seatback forward of the seated position.

Figure 16 shows the airbag at full deployment. Theairbag cushioned and prevented head impact into the

Elias, 7

Figure 15. AMSAFE Airbag Lap Belt RestraintSystem at 50 ms.

Figure 16. AMSAFE Airbag Lap Belt RestraintSystem at Full Deployment.

seat back while supporting the head to reduce loadingon the neck. This resulted in low HIC15 and Nijvalues, which were similar in magnitude to thoseseen in the lap/shoulder belt restraint tests. Althoughresults were similar between the two restraintsystems, testing of the airbag lap belt restraint systemwas very limited and did not include testing ofpossible misuse, or out of position, scenarios todetermine possible disbenefits of the system.

Discussion of Results

The data presented in the following figures representthe averaged results of the sled testing.

Compartmentalized and lap belted seats include thosemodels manufactured by BlueBird, Thomas Bus, andthe C.E.White Co., both the standard height and high

back model variations. The lap/shoulder belt datainclude the Bus Belt, C.E.White Co. and IMMI seats,while the lap/shoulder belt misuse tests wereconducted only with the C.E.White Co. seats in earlytesting. The airbag lap belt restraints (AMSAFE)were installed on BlueBird’s lap belted, reinforcedseat design. Individual test results are available onNHTSA’s Vehicle Crash Test Database (http://www-nrd.nhtsa.dot.gov/database/nrd-11/veh_db.html).

Figure 17 is a summary chart of the head injurycriterion results, HIC15, which has been normalized tothe pass/fail criterion value of 700. A value of 1.0 onthis chart represents a HIC15 of 700, or approximatelya 30 percent risk of serious injury.

The unbelted, or compartmentalized, tests had similarHIC15 results to those of the lap belt restraint tests forall age/size groups. While the lap belt restraintchanged the kinematics of the dummy’s impact intothe forward seat back, the overall velocity of the headimpact was comparable and both seat designs utilizeseat backs that meet the compartmentalized seat’sforce versus deflection requirements. Thelap/shoulder belt restraint tests, which typicallyprevented or greatly reduced the head impact into theseat back, had HIC15 response levels lower thaneither the compartmentalized or lap belt restraineddummies. The limited testing with the inflatableairbag lap belt restraint resulted in the lowest overallresponses for the 6-year-old and 50th percentile adultmale dummy while the HIC15 response for the 5th

percentile female dummy was comparable to that ofthe compartmentalized and lap belt restraineddummies. Film analysis of the tests suggests thatwhen the head was fully cushioned by the airbag, thevery low HIC15 values were observed. When thehead partially impacted the seat back, somewhathigher HIC15 responses occurred. However, it shouldbe noted that the HIC15 response for all of these testswere low and represent a low risk of serious injury tothe occupant.

Figure 18 is a chart summarizing the neck injury(Nij) results. The FMVSS 208 pass/fail tolerancelimit for this criterion is 1.0, which represents a 22percent risk of serious neck injury. A value of 2.0equates to a 67 percent risk of serious injury. Boththe lap/shoulder belt restraint systems and theAMSAFE inflatable airbag lap belt system had lowerNij responses. The lap/shoulder belt restraintsreduced or prevented head impact, thus the onlyloading on the neck was the inertial loading of thehead. The inflatable airbag lap belt restraintcushioned the head impact while supporting the head,thus reducing the extension of the neck. The lap belt

Elias, 8

H IC

0 .0 0

0 .2 0

0 .4 0

0 .6 0

0 .8 0

1 .0 0

Com

part

.

Lap

Bel

t

L/S

Bel

ts

Lap

Bel

t

Air

Bag

L/S

-

mis

use

1

L/S

-

mis

use

2

6 Y e a rO ld

5 thF e m a le

5 0 thM a le

• “L/S misuse 1” - shoulder belt routed behind the dummy’s back• “L/S misuse 2” - shoulder belt routed under the dummy’s arm

Figure 17. Summary of Average HIC15 Values for Frontal Sled Tests.

Nij

0.000.501.001.502.002.50

Com

part

.

Lap

Bel

t

L/S

Bel

ts

Lap

Bel

tA

irB

ag

L/S

-m

isus

e1

L/S

-m

isus

e2

6 YearOld

5thFemale

50thMale

• “L/S misuse 1” - shoulder belt routed behind the dummy’s back• “L/S misuse 2” - shoulder belt routed under the dummy’s arm

Figure 18. Summary of Average Nij Values for Frontal Sled Tests.

Elias, 9

restraint tests showed a significant potential of riskfor severe injury for some seat spacing/dummystature conditions, while the “misuse 1” tests with thelap/shoulder belt restraints, which approximated a lapbelt restraint system, showed potential for a highdegree of risk for severe injury similar to that of thelap belt restraints.

Figure 19 is a summary chart of the average 3 msChest G results. The averaged data were normalizedto the 60 g criterion limit. None of the testsconducted with any of the restraint systems showedsignificant risk of serious injury. The generalkinematics, along with the closely spaced and paddedseat backs, provided good protection for theunrestrained and lap belted occupants. The shoulderportion of the lap/shoulder belt restraints didpotentially apply load to the chest, but the relativelylow peak acceleration levels within the passengercompartment of the bus limited this loading. Resultsfor the inflatable airbag lap belt restraint were similarto those for the lap/shoulder belt restraint, butappeared to be more occupant size dependent thansome of the other restraint systems.

Effect of Seat Back Height - The most significanteffect of increasing the seat back height, from theminimally required 508 cm (20 in) above the SRP,was the containment of the 50th percentile adult maledummy when tested in the compartmentalizedconfiguration. There were several tests in which anunrestrained 50th percentile adult male dummyoverrode a standard height seat back and struck adummy positioned in the seat in front. High HIC15

values were observed in these tests in which thisincidental contact occurred.

The seat back height, in general, did not appear to bea highly significant factor affecting the HIC15 and Nij

values observed for the 6-year-old and 5th percentilefemale dummies.

Effect of Seat Spacing - As stated previously, sledtests were conducted with the school bus seatspositioned at three different spacing – 48 cm (19 in),56 cm (22 in) and 61 cm (24 in). No consistenttrends were observed for any dummy size in thelimited number of tests with different seat spacing.

3 ms Chest Acceleration

0.00

0.20

0.40

0.60

0.80

1.00

Compart. Lap Belt L/S Belts Lap Belt Air Bag

6 YearOld

5thFemale

50thMale

Figure 19. Summary of Average 3 ms Chest G Values for Frontal Sled Tests.

Elias, 10

Concern about Abdominal Loading with Lap BeltRestraint Systems -When properly positioned, the lapbelt system restrains an occupant by loading themacross the hard pelvic structure. When used inconjunction with a shoulder belt, a portion of the loadis also distributed across the upper torso. When a lapbelt restraint is improperly positioned, due toimproper fit or misuse, this load produced by the beltcan be transmitted to the occupant through the softabdomen, rather than across the hard structure of thepelvis. This has been shown to produce serious-to-fatal injuries in automotive crashes.

Current frontal crash test dummies are not designedto measure abdominal forces, and there are no criteriacurrently available to predict injury if such forceswere determined. While some efforts were made tomeasure these loads in the first series of sled tests, theresults were largely inconclusive. The data fromthese tests were reported in NHTSA’s April 2002Report to Congress, “School Bus Safety:Crashworthiness Research” [2] and are available onNHTSA’s Vehicle Crash Test Database.

SIDE IMPACT RESEARCH

Research of the available crash data by NHTSAindicates that being impacted in the side by a heavytruck is, after front and rear impacts, the next mostprevalent source of serious injury or fatality to schoolbus occupants. The agency conducted a side impacttest in which a heavy truck (a cab-over tractorballasted to 11,406 Kg) was towed into the side of aschool bus at 72.4 km/h [1]. Despite the severity ofthis crash, the dummy responses indicated nosignificant threat of severe injury to those occupantslocated outside of the direct impact zone.

NHTSA is conducting ongoing research to quantifythe magnitude of the injury problem to school busoccupants during a side impact, and to evaluatepotential methods for mitigating these injuries. Crashdata analysis is continuing to better define theconditions and locations of head impacts that produceinjury to occupants in bus crashes. Also, the agencyis contracting with Mercer University’s EngineeringResearch Center (MERC), in a joint research effortto: (1) develop a finite element model of a typicalschool bus construction, and (2) study the effects onoccupant protection of various levels and types ofpadding added to the bus sidewall and/or roof area.

The agency’s Vehicle Research and Test Center(VRTC) has conducted a series of preliminarydynamic component tests to assess the threat of head

injury when contacting various portions of the upperinterior of the school bus. This includes the roof andareas surrounding the side windows and emergencyexits. These tests used the free-motion head-formspecified for use in FMVSS 201 to evaluate thepotential for head injury and to identify potentialinjury mitigating structures currently present in somebuses.

CONCLUSIONS

The following conclusions are based on the resultsfrom the Initial [1] and Phase II sled test series(discussed in this paper):

1) Compartmentalizationa) Low head injury values were observed for

all dummy sizes, except when overrideoccurred (i.e., when the large male dummyoverrode the seat in front of it).

b) High back seats prevented this overridephenomenon from occurring.

c) Approximately half of the tests with the 6-year-old and 5th percentile female resulted inhigh Nij values.

2) Lap Belt Restraint Systema) Lap belt restraints effectively kept the

dummies in their seats.b) HIC15 values were low for all dummy sizes.c) Nij values were high for most of the

dummies, and were generally higher thanthose from the compartmentalization tests.

d) Neck injury potential was very sensitive toseat spacing and occupant size, with manytests producing Nij values in excess of twicethe criterion threshold.

3) Lap/Shoulder Belt Restraint Systema) Lap/shoulder belt restraints effectively kept

dummies in their seats.b) HIC15 values were low for all dummy sizes.,

and were significantly lower thancompartmentalization and lap belt restraintresults.

c) When the restraints were properly worn, theNij values were below the criterion value forall size dummies.

d) Restraint misuse – putting the shoulder beltbehind the dummy’s back or under thedummy’s arm – can produce undesirableresults.

e) The stiffer seat back, required for anchoringthe shoulder belt upper anchorage, couldpresent a potential problem for the unbeltedoccupant(s) seated behind an occupant who

Elias, 11

is secured with the lap/shoulder beltrestraint.

f) Stiffer seat back design issues may beaddressed by proper design and/or paddingof the seat.

4) Inflatable Airbag Lap Belt Restraint Systema) The airbag lap belt restraint appeared to

cushion and/or prevent head impacts into theseatback in front of the occupant.

b) The restraint system appeared to support theoccupant’s head, reducing loading on theneck.

c) HIC15, Nij and 3 ms chest g values weresimilar in magnitude to those observed forlap/shoulder belt restraints.

REFERENCES

1. Elias, J.C.; Sullivan, L.K. and McCray, L.B.,“Large School Bus Safety Restraint Evaluation”,17th International Technical Conference on theEnhanced Safety of Vehicles, Amsterdam, June 4-7, 2001.

2. United States Congressional Report,“School Bus Safety: Crashworthiness Research”,April, 2002. Available at http://www-nrd.nhtsa.dot.gov/departments/nrd-11/SchoolBus.html