When would you be better off not wearing your seatbelt?

My friend Eddie's Uncle Joe heard about this truck driver who narrowly avoided a fiery wreck by plunging his truck through the gaurdrail and down a 100 meter cliff. If he had had his seatbelt on, he would never have been able to jump out at the last second and hang on to the gaurdrail. 我朋友Eddie的叔叔乔听说有位卡车司机险些在一场烈火中的车祸中丧生，他冒险将卡车冲进护栏并翻下100米高的悬崖。如果他系了安全带，就不可能在最后一刻跳出来抓住护栏。 Maybe so. 也许如此。 But the work-energy principle must be satisfied in every collision, and it dictates that the work done in stopping the driver must be equal to the driver's kinetic energy. The shorter the stopping distance, the greater the impact force. And cases where the seatbelt would not lengthen your stopping distance and decrease your impact force are about as rare as this kind of accident. 但工作-能量原理必须在每一次碰撞中得到满足，它规定了在使驾驶员停止过程中所做的功必须等于驾驶员的动能。停止距离越短，冲击力越大。而安全带不会延长停止距离并减小冲击力的情况，其罕见程度与这种事故的罕见程度相当。 Rather than making judgements about safety from anecdotes like the one above, it is wise to consider the evidence from the large database on traffic fatalities. 与其根据上述例子中的轶事来判断安全性，不如考虑来自交通死亡大数据库的证据。

Seatbelt and Airbag for Safety

While the driver with an airbag may experience the same average impact force as the driver with a good seatbelt, the airbag exerts an equal pressure on all points in contact with it according to Pascal's principle. The same force is distributed over a larger area, reducing the maximum pressure on the body.

The presence of an airbag should not be used as justification for not wearing the seatbelt! The seatbelt keeps the driver from moving out of the position where the airbag is effective in capturing the driver and cushioning the impact.

Protection by Seatbelts

Data on seatbelt effectiveness was obtained by comparing severe accidents in which at least one person was killed. An effectiveness of 42% for drivers with seatbelts means that a 42% reduction in fatalities would occur if all drivers wore seatbelts.

Vehicle Mass and Accidents

Traffic Accident Data

Trucks: more likely to 'win' in car crash

Phil Frame, a spokesman for the National Transportation Safety Board, said that while large trucks are not part of most deadly wrecks, "they are overrepresented in the number of fatal accidents they are involved in."

In 1997, they accounted for 9 percent nationally of all vehicles in fatal wrecks, but accounted for only 3 percent of all registered vehicles and 7 percent of total vehicle miles traveled, the national transportation statistics show.

"The greater mass vehicle almost always wins in a vehicle crash", Frame said.

78 percent of the people who died after collisions with big trucks were occupants of the other vehicle, and 75 percent of the people who were injured were in the other vehicle."

Excerpts from "Facts counter fear about big rigs", by Jennifer Brett, Atlanta Journal.

Spokesmen for the trucking industry are quick to point out that truck drivers are better trained, and safer drivers than the general public - and that is believable. But just the physics of collisions dictates that the occupant of the less massive vehicle is more at risk when a collision does occur.