School Bus Transportation News at STN Media

School Bus Safety Study

Volume I
Traffic Safety Standards and Research, Transport Canada
Prepared by: G.N. Farr, P.Eng.
Automotive Safety Engineer
Crashworthiness Section
Date: January 1985

Webmaster Note: Selected excerpts of volume 1 the 131 page "School Bus Safety Study" by Transport Canada are presented here.
Interested parties should contact Transport Canada at 613/998-8616 to obtain a complete copy of the report. Click here to visit the Transport Canada website.

A critique of the Transport Canada tests by the National Coalition for Seat Belts on School Buses is also presented here.

Abstract
The safety of children on school buses is an issue of considerable concern. Canadian Motor Vehicle Safety Standards pertaining to the crashworthiness features of school buses were introduced in 1980 with the objective of better protecting children in the event of an accident. While there is not yet sufficient accident data available in Canada to document the effects of these regulations there are indications in the U.S. that similar regulations have been effective in accomplishing this goal. The suggestion has been made by many groups, in many occasions, that perhaps seat belts should be made mandatory in school buses in order to provide an enhanced level of occupant safety.

This report details the results of an overall study of school bus safety. It includes the results of a literature survey, discussions with bus manufacturers and operators of school buses utilizing seat belts and a crash test program for three different school buses.

The crash test program provided data and photographic evidence to compare the reaction of three belted and three unbelted dummies in a 48 km/h frontal collision. Three different seat spacings were also used.

The results indicated that the belted dummies experienced higher head accelerations, lower chest accelerations and more severe neck extension than did the unbelted ones. This indicates that if lap belts are installed on current designs of school bus seats, a greater potential for head injury may exist.

Other observations suggest that further study is required in the areas of glazing strength, attachment of seats to floor, fuel filler mounting and driver protection.

Summary
Tests of three school buses were conducted to determine the adequacy of the current occupant protection standards in preventing death and injury, and also to determine the effect of seat belts on the level of occupant protection. The school buses were run into a fixed collision barrier at 48 km/h., with belted and unbelted instrumented dummies being used to estimate injury. The results indicate that, in a frontal collision belted school bus occupants are liable to suffer more serious injury than unbelted ones.

Introduction
The safety of children on school buses is an issue of continuing concern and the suggestion has been made frequently that the installation of seat belts should be made mandatory in order to provide an enhanced level of safety. However, Canadian Motor Vehicle Safety Standards were amended in 1980 to improve the crashworthiness features of school buses, with the objective of better protecting children in the event of an accident. While there is not yet sufficient accident data available in Canada to document the effects of these regulations there are indications in the U.S. that similar regulations introduced in 1977 have been effective in accomplishing the goal of improved safety.

Accident studies show that school buses are the safest means of transporting students to and from school. The latest available Canadian analysis concluded that a student is 8 times more liable to be injured while travelling to or from school in a vehicle other than a school bus. The data on which this observation is based, are, however, sparse and further collection and analysis of accident information should be pursued. Specifically, the direction if impact and the type of injuries incurred should be documented.

There are at present a total of thirty five federal safety standards which are applicable to school buses. Of these, four new sets of requirements introduced in 1980 ensured that school buses would be constructed with improved occupant protection, increased body joint strength, improved window retention, and better fuel system integrity.

There are several factors other than the occupant protection characteristics of the vehicle which contribute towards school bus safety. School buses travel at low speeds between stops, during specific times of the day, and on predetermined routes. They are a unique colour, employ special flashing lights and in many provinces, stop arms to warn other motorists when they are stopped for loading and unloading. In addition, provincial regulations make it an offense to pass a stopped school bus, with its warning lights activated while it is loading or unloading students.

As a result of extensive testing in the U.S. and Canada, the occupant protection capability of school buses was greatly improved by requiring the use of high backed, heavily padded, closely spaced seats. In addition, a high, padded barrier was required to be installed ahead of the front row of seats. These passive protection features are intended, in the event of an accident, to keep the occupants in a relatively harmless environment, thereby preventing serious injuries occurring. These features combine to form what is colloquially known as the compartmentalization concept.

In order to test this concept and to estimate the effects of using lap seat belts in schoolbuses a series of school bus collisions were conducted at Transport Canada's Motor Vehicle Test Centre at Blainville, Quebec, with technical assistance being provided by Arvin Calspan of Buffalo, N.Y.

Description of Tests
Three different sizes of school buses, representing the majority of types of vehicles used for transporting school children in Canada today, were subjected to a barrier collision at 48 km/h. The forces generated during such a test crash are comparable to those resulting from a head-on collision between the school bus and a car travelling at highway speed. The buses consisted of a large 66 passenger Blue Bird conventional type, a mid-sized 22 passenger Thomas Minotour, and a small, 20 passenger Campwagon van conversion.

Each bus contained six 5th percentile adult female test dummies* to represent large elementary school students. Three different seat spacings representing all practical forward facing seating configurations were also incorporated in the buses.

The dummies were instrumented to record forces on the head and chest during the collision. Three dummies were secured in place by lap seat belts and three were left unrestrained. The dummies were arranged in pairs in the buses so as to provide one restrained and one unrestrained dummy for each seat spacing arrangement. High speed cameras recorded the motion of the dummies during the collisions.

The Head Injury Criterion (HIC), which produces a mathematical combination of resultant head acceleration and the duration of that acceleration, was used to estimate the degree of harm occupants might suffer in the collision. This technique has limitations in its ability to predict injury but is the only widely accepted measure currently available. Resultant chest acceleration was used to estimate the degree of harm that might be suffered in that body region.

For this analysis, the limit of 1000 for HIC is used as the threshold above which serious injury or death could be inferred. An upper limit of 60g for resultant chest acceleration is the threshold used when determining the severity of this variable.

Results
The Head Injury Criteria and maximum chest accelerations, together with quantifiable information on the behaviour of the vehicle during the tests are given in table 3.

During the impact of the large Blue Bird bus its body structure moved 775 mm. forward relative to the chassis. The front right-hand side door was rendered inoperable but all emergency exit windows and the rear emergency door remained in working order. The hood encroached significantly into the driver's occupant space. There was no separation of body joints.

During the impact of the Thomas Minotour bus the body structure moved 381 mm forward relative to the chassis. The window in the driver's door was cracked but the door itself remained in working order. The right-hand front door opened early during the collision event and remained open after the vehicle and come to a standstill. The side emergency window exits and rear emergency door remained in working order following the collision test. There ware no body joint separations.

During the impact of the Campwagon bus the left-hand side front and rear windows shattered. The driver's door was inoperable following the collision but the right-hand door and rear emergency door remained in working order. The floor attachments of the padded barriers and one seat support leg failed.

Discussion
In general the results indicated that the belted dummies experienced higher head and lower chest accelerations than did the unbelted ones. Furthermore, from the film data the belted dummies experienced more severe neck extensions due to the angle at which they struck the seat ahead of them than did the unbelted ones. The neck extension of several restrained dummies was judged to be life threatening. Dummies restrained by seat belts in both of the small buses experienced HIC values in excess of 1000, whereas the unrestrained dummies experienced HIC values of less than 1000. In the large bus all dummies experienced HIC values of less than 1000 but the restrained ones experienced values approximately three times greater than those for the unrestrained ones. This difference can be explained by the fact that the restrained dummies' heads struck the seat backs in a manner that did not permit efficient energy absorption by those seat backs. Sharp peaks in the head acceleration traces indicate that the dummy heads compressed the seat back padding to such a degree that they "bottomed out" on the steel structure underlying the padding in the seat back.

In all cases except one the chest accelerations were less that the life threatening criterion of 60 g's and the exception only exceeded the criterion by .4 g. For the Blue Bird and Thomas buses the unbelted dummies experienced higher chest accelerations than did the comparable belted dummies. This is to be expected since the chest of the unrestrained dummies transmits the majority of collision energy to the seat back ahead of it. Of the three pairs of dummies in the Campwagon bus, however, only one pair of dummies exhibited this trend; in the case of the other two pairs the reverse trend was exhibited for inexplicable reasons.

It should be noted that after all the collision tests the majority of exit provisions were still available for use by the occupants.

The movement of the body of the Blue Bird and Thomas buses reduced the severity of the impact for all occupants except the drivers, who would in all likelihood have died due to severe structural deformation which practically eliminated their occupant space. Comparison of the vehicle test data show that the two separately-bodied vehicles (Blue Bird and Thomas) experienced significantly lower decelerations than the unit bodied vehicle (Camp-wagon). The smaller amount of vehicle crush in the unit-bodies vehicle further contributes to this difference in collision severity.

Of the other aspects of structural behaviour the window breakage was considered to be serious for two reasons; failure of the window would permit ejection of the occupants and the glass fragments could be injurious. In addition, the seat and restraining barrier attachment failures were considered to be serious. These components were attached by lag screws which rely purely on their threading action in the floor to withstand any applied loads.

While the objectives of these tests did not include testing for fuel system integrity the fuel system performance during the collisions is of note. For the Blue Bird bus, the small chain which secures the fuel filler cap to the fuel tank became wedged between the edge of the filler cap body and the integral pressure relief disc. If a rollover had occurred, there would have been a fuel spill. For the Thomas bus, the fuel tank is secured to the chassis and the filler cap is secured to the body. A length of rubber hose is used to connect the filler to the tank. As a result of the body shift during the collision, this rubber hose broke loose from the fuel tank. Major fuel spill would have occurred if the bus had rolled over.

Conclusions
1. The passive occupant protection of the seating system, required by federal regulation since 1980, functions as intended during frontal impacts and provides excellent protection for occupants.

2. The use of lap seat belts in any of the 3 sizes of recent model school bus which were tested may result in more severe head and neck injuries for a belted occupant than for an unbelted one in a severe frontal collision. 3. The use of lag screws to attach seats and barriers to the bus floor appears to be inadequate for some vehicle designs.

4. The movement of the body along the chassis, as permitted by the attachment clamps which provide relatively weak longitudinal resistance to load, presents a life-threatening hazard to the bus driver.

5. The body joint strength regulation appears to be effective in preventing joint separation in the large school bus (Blue Bird).

2. The use of a type I seat belt system in any of the three sizes of recent model school bus which were tested may result in more severe head and neck injuries for a belted occupant than for an unbelted one, in a severe frontal collision.

3. The use of lag screws to attach seats/barriers to the bus floor appears to be inadequate for some vehicle designs.

4. The body shift along the chassis during a frontal collision presents a life threatening hazard to the bus driver.

5. The body joint strength regulation (CMVSS 221) appears to be effective in preventing joint separation in a school bus with a GVWR greater than 4500 kg during a frontal collision.

6. The window retention regulation (CMVSS 217) should be reviewed to determine if a minimum force should be applied to the windows before they are permitted to shatter or become dislodged from their frame.

7. The femur loads measured on ATD 4, 5 and 6 were well below the limit of 2500 lbs.

8. There are few statistics available concerning school bus accidents. Further collection and analysis of such data should be pursued. In particular, the direction of impact with the bus and the type of injuries encountered should be documented more fully.

*Anthropomorphic test device complying with Part 572 of the US Code of Federal Regulations.