National Coalition For School Bus Safety

NATIONAL COALITION OF SCHOOL BUS SAFETY NEWS 2004

The Great Seat Belt Debate (continued)
(Revised June 21, 2004)

A Philosophical Difference

Clearly, the only certainty to emerge from this long-standing, dispute is that agreement is elusive. Well-meaning people on both sides of the debate -- professional school transporters, manufacturers, the medical community, government officials, researchers, parents, school administrators, safety officials, child safety advocates -- often disagree. It is not unusual that interested parties can look at the same data -- indeed the same school bus accident -- and draw opposing conclusions.

While opponents point to the safety record of school buses and say that compartmentalization works, proponents cite rollover and side impact accidents, and injuries, and demand seat belts.

In the late 1960s, during the infancy of occupant protection research when the Great Seat Belt Debate in school buses first became an issue of intense public interest, 2-point lap belts were found in most automobiles that offered any kind of active occupant restraint system. An important development occurred in 1963 when Volvo was the first to introduce 3-point lap/shoulder safety belts in the front seat as a standard feature in the automobiles it offered for sale in the USA.

In 1967 the National Highway Safety Bureau issued "FMVSS 208: Occupant Crash Protection," and "FMVSS 209: Seat Belt Assemblies," setting standards for lap and shoulder belts in front outboard positions and lap belts in all other positions. Within a decade NHTSA issued or amended FMVSS 201: "Occupant Protection in Interior Impact," FMVSS 207: "Seating Systems," FMVSS 210: "Seat Belt Anchorages," and FMVSS 213: "Child Restraint Systems," completing the elements of an active restraint system. In the coming decade, U.S. automakers began offering the 3-point safety belt system in their models. But the school bus seat belt debate remained focused on the 2-point lap belt.

During rulemaking of FMVSS 222 in the early to mid 1970s, NHTSA made an intentional, reasoned decision in favor of compartmentalization and rejected lap belts for large school buses.

FMVSS 222 requires school bus seat backs to bend at 1,000 lbs. force. This bending action causes the seat back (indeed the entire bus) to absorb some of the crash forces, in turn reducing the crash forces absorbed by the passengers seated inside the school bus.

The flexible seatback requirements of FMVSS 222 are different from the passenger occupant protection requirements of FMVSS 208, which regulates automobiles and small school buses. FMVSS 208 requires seat belt anchorages and anchorage hardware to withstand 5,000 lbs. force per anchorage! Plus, FMVSS 208 requires occupant restraint anchorages to be attached to a structure in the vehicle that will support it.

Another factor that permits compartmentalization to work is seat spacing. FMVSS 222 establishes seat spacing at 24 inches apart or about 60 centimeters. Researchers for Transport Canada and the important FRG/TOV Rhineland study in West Germany found the optimum distance between seats equipped with seat belts to be approximately 85 centimeters or 35 inches! Closer than that exacerbated the whiplash effect of lap belts, significantly increasing the possibility and severity of head, neck and spinal injuries. The fact is that seats in all large school buses currently on the road are spaced too close to safely accommodate 2-point lap belts!

Further dampening federal enthusiasm for two-point lap belts, the U.S. Department of Transportation (and independently, Transport Canada, the Canadian federal government's transportation agency) concluded that lap belts should not be required on large school buses.

In its seminal report, "Improving School Bus Safety, Special Report 222," the National Academy of Sciences' Transportation Research Board noted "...the overall potential benefits of requiring seat belts on large school buses are insufficient to justify a federal requirement for mandatory installation." This view became official U.S. policy.

Another factor in the debate is Newton's Law of Motion. This law has to do with a body in motion and the forces exerted on it. Simply put, there are huge differences between the crash forces generated when a large school bus -- typically 22,000-to-25,000 lbs. -- collides with a tree or stone wall, compared to the crash forces generated when a 3,500 lb. automobile, a 66,500 lb. tractor-trailer, or a 700-ton commuter train as occurred in the Fox River Grove train-school bus collision in November 1995 collides with a school bus.

In the Fox River Grove crash, NHTSA's Hott calculates that at the moment of impact the Metra commuter train, traveling at about 55 to 60 mph at the moment of impact, delivered 151,000,000 (that's 151 million) foot-pounds of kinetic energy to the then-stationary school bus. Seven youngsters lost their lives in that horrific accident. Reader please note: The absence of seat belts had nothing to do with these fatalities. It was the force of the impact!

Meanwhile, the Snyder, Okla. school bus accident of Nov. 10, 1993 offered a different outcome, one that argues forcefully in favor of lapbelts. In this crash a large truck traveling an estimated 55 to 60 mph broadsided a small, 20-passenger school bus. The bus had a gross vehicle weight rating (GVWR) of 10,000 lbs. and its actual estimated weight was 8,324 lbs. The estimated weight of the conventional tractor-truck and its loaded semitrailer was 66,500 pounds. Using the same calculation, the kinetic energy of the tractor-trailer when it struck the small school bus was about eight million foot-pounds of energy. The bus was equipped with seats in compliance with FMVSS 222 and with lap belts. All eight of the unbelted passengers were ejected, four were fatally injured and two were seriously injured. The single belted child had only minor injuries. According to the NTSB ejections would not have occurred, injuries would have been less severe, and lives would have been saved if more of the occupants of the bus had been wearing their lapbelts. Here is what the NTSB wrote in its final report of the Snyder crash:

"The (National Transportation) Safety Board concludes that if the unrestrained passengers had been wearing the available lapbelts, none of them would have been ejected: Prospects for survival might have been better for three of the children who were killed (passengers 6, 8, and 9). Two of the children who survived (passengers 3 and 5) might have received less severe injuries. One seriously injured child who survived (passenger 4) might have been killed, depending on her position on the bench seat. For two children (passenger 1, who received minor injuries, and passenger 7, who was killed), the outcome probably would have been the same." NTSB's Snyder, Okla. Highway Accident Report, p. 33

A group known as the National Coalition for Safety Belts offers an excellent explanation of crash dynamics in a vehicle collision. It explains that a vehicle collision actually comprises three separate collisions: (1) the "car collision" when the vehicle comes to an abrupt stop, (2) the "human collision" when the human occupant strikes some part of the inside of the vehicle, and (3) the "internal collision" when a passenger's internal organs are still moving forward and then come to an abrupt halt. The coalition then argues for 3-point lap/shoulder safety belts as the appropriate restraint system.

Meanwhile, the authors of the Transport Canada seat belt study point out: "The school bus presents a different problem with respect to occupant protection, unlike passenger cars, whose more aggressive interior, lower mass and more severe deceleration behavior in a crash situation makes the fitment of seat belts essential for occupant safety...." Severe deceleration indeed! You know the old saying, "It's not the fall that kills you, it's the sudden stop at the end."

Truth be known, Sir Isaac Newton's Laws of Motion are more germane to the Great Seat Belt Debate than the fervor of either the opponents or proponents.

The Future of the Great Seat Belt Debate

Perhaps the discussion should now be known as the "lap/shoulder belt debate." With adoption by Louisiana and California of legislation requiring lap/shoulder belts on large school buses, and now that three-point lap shoulder belt systems are available commercially, the movement to install an active occupant protection system in large school buses is off to a new start. Moreover, NHTSA has announced that it intends to revisit the issue during rulemaking in 2004-05.

Buckle up!

COMMENT BY Arthur L. Yeager, DMD, MMH
Unfortunately, the analysis falls short because it does not include the conclusions of the September 1999 NTSB that found compartmentalization was incomplete and failed to protect in lateral and roll over accidents. NTSB asked NHTSA to come up with a system to protect in side and rollovers, but to date, almost 5 years later, nothing has emerged.

The NTSB report is at http://www.ntsb.gov/publictn/1999/SIR9904.pdf

top