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Some Things You Should Know About Seat Belts

As Originally published by National Bus Trader, January 2009.

By: Ned Einstein
Tel: 212-766-1121
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As pressure from the unknowing continues to mount, rumors have it that the U.S. motorcoach industry is slowly inching toward the installation of seatbelts. That we are doing so by skipping the decades of seat compartmentalization that has helped fend off most seatbelt advocates in the schoolbus industry is only more unfortunate since existing motorcoach seats lend themselves to a far more evolved form of compartmentalization than the "incomplete compartmentalization" (in NHTSA's own words) of their yellow body-on-chassis cousins.

Mass and Ejection

The principal purpose of seatbelts and compartmentalization is to keep the passengers in their seats. This principle is recognized as important as most fatalities occur when passengers are ejected through the bus' windows. Ejection is less likely in schoolbuses partly because their windows are considerably smaller, and because two Federal requirements - FMVSS #217 and #220 - have established standards for schoolbus window retention. The spacious windows of motorcoaches meet no such standards, and unrestrained by any form of containment, victims of severe or catastrophic accidents are easily jettisoned through them into the cold night air.

Seatbelts necessarily involve trade-offs in any and every type of vehicle in which they are installed. Particularly for children whose internal organs are not fully developed, the impact of seatbelts - particularly lapbelts - on these organs can lead to serious internal injuries. This trade-off is considered acceptable in automobiles because, frankly, it's a better risk than ejection. But in vehicles whose mass is 10 times that of most things with which they would likely collide - and g-forces impact colliding bodies as the square of their differences in mass - buses pretty much wipe out most things in their way with little effect on their passengers. I am currently working on a lawsuit where a runaway bus hijacked by a hallucinating junkie wiped out seven cars before coming to a halt against a stone wall. With the likelihood of ejection from such heavy vehicles rare, the trade-offs involved with seatbelts are not worth the price often paid by their occupants.

Compartmentalization and Participation

Even without seatbelts, the likelihood of ejection from schoolbuses is also minimized by the genuine "compartmentalization" of their seats. Compartmentalization is more than simply lining up rows of cushy, forward-facing seats spaced reasonably close together. When a passenger flies forward (for example, from a head-on collision), his or her torso generally collides with the seatback in front in willy nilly fashion. Compartmentalized seats control this movement through variations in the density of the foam at different parts of the seatback. Because one's knee generally strikes the seatback first, the foam density in the lower part of the seatback is designed to absorb this impact and slow down the rest of the passenger's torso flying forward. Less dense foam in the upper quadrant then cushions the impact of the passenger's arms and shoulders, a cushioning that further decelerates the speed of the passenger's head moving forward. The beauty of this approach is that, for it to operate, the passenger need do nothing but remain in his seat.

Seatbelts pose a completely different dilemma, depending upon whether the system involves only a lap belt or three-point belt system. Lap belts present two distinct problems:

  1. Because they do not restrain the forward movement of the upper torso, the belt's "envelope of restraint" is often less than the spacing between the seats. So restrained only at the waist, lap-belted passengers' heads can still strike the seatbacks in front of them. While this presents a particular problem in closely-spaced schoolbus seats, at least most of their passengers are small enough to remain within the envelope. In contrast, while motorcoach seats are spaced slightly further apart, most of their occupants are considerably larger, and with belts fastened only at the hips, their forward movement would exceed the "envelope of restraint" formed by the seat spacing.
  2. Far worse, when an unrestrained passenger flies forward, his or her torso absorbs most of the impact. When this passenger is lap-belted in place, however, his or her waist becomes a fulcrum, and accelerates the movement of the passenger's head into the seatback in front. Much of the testing of lapbelts conducted in the 60s and 70s found that head impact crash values (referred to as HIC values) where the anthropomorphic dummies' heads survived became lethal when lap belts were attached to their torsos and their heads accelerated dramatically more forcefully into these same seatbacks.

Three Versus Two

Three-point seatbelts address both these shortcomings of lapbelts: Their "envelope of restraint" contains the passengers within the space between the seatbacks. And in doing so, the shoulder belt portion of the restraint system prevents the passenger's head from reaching the top edge of the seatback in front, much less at a lethal speed and force.

But three-point belts have other problems. They are more difficult to get out of - particularly following an accident. And the chances of getting hung upside down in a rollover, and being unable to extricate oneself from the belts, is far greater. Further, shoulder belts expose the passengers to more neck injuries from side- and oblique-impact collision orientations.

A fundamental downside to both types of belts is the fact that, in order for them to provide any protection to passengers, the passengers must wear them.

Carts and Horses

At even this elementary level of analysis, it is obvious that the motorcoach industry is making a serious mistake by leaping ahead to seatbelt containment before compartmentalizing its seats. The perfect solution would be a compartmentalized seat and a three-point belt system - the latter of which could be sold as an optional feature. But with the existing structure of motorcoach seats - high-back, contoured, bucket seats with armrests - the starting point exists for developing a far superior compartmentalized seat than schoolbuses have, since the incomplete compartmentalization of schoolbus seats provides their passengers with no protection in side impact collisions, and only marginal protection in oblique impact collisions. Further, with flat bench seats and no armrests, compartmentalized schoolbus seats provide only limited protection from rebounding - the phenomenon by which passengers bodies fly about in multiple directions following the initial thrust from the impact, often banging their heads into one another. Even without compartmentalization, a motorcoach seat that already contains greater height, arm rests, contoured seat cushions and often headrest supports would limit rebounding to a far greater degree than schoolbus seats - with the exception, of course, of the initial absorption of impact forces, for which schoolbus seats are admittedly superior.

With their smaller windows and window retention standards, the even incomplete compartmentalization of schoolbus seats provides far superior protection - particularly in terms of preventing ejection - than do current motorcoach seats. But the remedy is not to ignore compartmentalization and jump to seatbelts - particularly lapbelts. Remember: The restraint system is only as good as the wisdom of the occupant to wear it. For the unwise, seatbelts provide no protection, irrespective of whether they contain two or three sections. For this reason, skipping the compartmentalization stage that schoolbuses have enjoyed for more than three decades - an approach that has kept seatbelt advocates at bay in all but seven states - is not like placing the cart before the horse. It is like removing the horse and letting the cart crash into the wall without the padding that the horse would otherwise provide.

Words to the Unwise

European and Australian motorcoaches contain three-point seatbelts. But European roads are far superior to ours, and European passengers are far more willing to wear their belts - a phenomenon easily documented by their willingness to mandate their installation. The same is not true of Americans. In our zeal to "skip the horse," scores if not hundreds of lives will likely be lost as we adjust to the use of a technology that many American passengers do not seem to even want.

I fully expect many members of the motorcoach industry to find these comments intriguing. Yet it would be a big plus if the OEMs (including a plethora of European motorcoach manufacturers whose models have been equipped with three-point belts in numerous markets for decades) and seat manufacturers responded to these issues as a challenge rather than as a criticism. It would be a bigger plus were one of them to seriously invest in a technology that is not only superior to seatbelts, but which would provide a cogent argument for not installing them altogether. Without this argument, some form of seatbelts will undoubtedly lie in our future, despite all the kicking, screaming and lobbying.

Strapping a bunch of passengers to a horseless cart and hurling it along the freeway is not the way to ensure their safe arrival. Without the horse, the cart itself can take us only so far.

Ned Einstein is the President of Transportation Alternatives, a passenger transportation and automotive consortium engaged in consulting and forensic accident investigation and analysis (more than 600 cases). Specializes in elderly, disabled, schoolchildren. Mr. Einstein has been qualified as an Expert Witness in accident analysis, testimony and mediation in vehicle and pedestrian accidents involving transit, paratransit, schoolbus, motorcoach, special education, non-emergency medical transportation, taxi, shuttle, child transport systems and services...

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