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WHY PASSENGER SURVIVABILITY CANNOT BE COMPLETELY ASSURED IN HEAD-ON VEHICLE IMPACTS AT CURRENT LEGAL SPEED LIMITS Gustavo Zini School of Engineering – University of Buenos Aires Argentina Paper Number 09-0210 ABSTRACT weeks in hospital after severe crashes and many will never be able to live, work or play as they used to do. “This impact is intended to represent the most Current efforts to address road safety are minimal in frequent type of road crash, resulting in serious or comparison to this growing human suffering”. (World fatal injury. It simulates one car having a frontal im- Health Organization, [1]) pact with another car of similar mass”. (EuroNCAP frontal impact procedures). Safety first. It can be argued that human bodies are poorly No one doubts this should be the ground rule in prepared to support direct hits from hard objects. On every aspect of automobile transportation. Yet, it is the other hand, there are proofs of resistance to very important to meditate on this: is it possible to, always, high decelerations, provided they are held for ex- put safety first? tremely short periods of time. Yet, in front-to-front It is understood that the question cannot be an- vehicle impacts, a third phenomenon that can be swered simply, and will not be responded here. What compared to direct hits takes place: instantaneous will be regarded instead, is if putting safety first is changes of speed. applicable to head-on collisions. On top of that, and Most modern vehicles are nowadays tested thor- deeming that head-on impacts are intended to repre- oughly to evaluate their capability to protect their sent the most frequent type of road crash resulting in occupants in case of frontal impacts. But these tests serious or fatal injury, some reasons will be high- are performed under the premise that the vehicle is lighted, explaining that survivability cannot be com- having an impact with another car of similar mass pletely assured when mentioned impacts take place. that is traveling at the same speed. These conditions To begin with, it can be said that when a collision lead to an incomplete analysis of the complex phe- occurs —no matter if is is a head-on one, or other— nomena that take place in a real front-to-front vehicle passenger survivability depends on how kinetic en- since it is statistically improbable that a vehicle will ergy is managed. Speed and mass of the colliding crash with another one that has both the same mass vehicles will determine how much kinetic energy will AND speed —and in this scenario, the vehicle with be transformed during the phenomenon. And depend- the lesser kinetic energy will unfailingly suffer an ing on the way in which the structure of the vehicle instantaneous change of speed—. absorbs this kinetic energy, the car will deform and This paper will confirm the lastly mentioned issue passengers will be exposed to potentially dangerous using basic physics models (namely mass-spring directs impacts, or deceleration phenomena. models), and will discuss the the way of combining As it will be explained with more detail later on, it structural integrity and occupant restraints to ensure can be argued that direct impacts produce more dam- the maximum possible protection. This will be done age to human organs than high levels of acceleration from a general and synergistic point of view, and will during extremely short periods of time. Moreover, a point out some aspects that should be developed thor- third event can harm passengers in a manner that is oughly within the corresponding settings and using closer to direct impacts than to extreme decelerations: appropriate resources. instantaneous changes of speed. Unfortunately, at current speed circulation, and with the type vehicles that are used the three mentioned events occur in INTRODUCTION most car impacts. That is to say passengers are com- monly exposed to direct impacts, instantaneous “Every day thousands of people are killed and changes of speed, and high levels of decelerations. injured on our roads. Men, women or children walk- ing, biking or riding to school or work, playing in the It can be argued that there are certain procedures streets or setting out on long trips, will never return that can be implemented to avoid both direct impact home, leaving behind shattered families and commu- and potentially deadly decelerations, specially under nities. Millions of people each year will spend long the circumstance of impact against direct objects. On ZINI 1 the other hand, it can be proved from a Physics points Among many others, the 1934 Chrysler Airflow of view that there is no way to avoid that one of the case can be mentioned. It was full of engineering in- two vehicles of a head-on impact suffers an instanta- novations —an aerodynamic singlet-style fuselage; neous change of speed. So, if this is the case, and steel-spaceframe construction; near 50-50 front-rear considering what experts in the biomechanics of weight distribution; light weight—. However, as it trauma know about injury mechanisms: was, the car's dramatic streamliner styling antago- ➡ is it possible to design automobiles in order to nized Americans on some deep level, and sales were avoid exposing passengers to mortal instantane- abysmal. ous changes of speed during head-on collisions? ➡ if this is not situation, shouldn`t speed limits be lowered to assure survivability? PUTTING SAFETY FIRST “And, by the way, there is only one goal, no mat- ter what the company”. (Eliyahu Goldratt, [2]) The Great God Car. It can be said that an automobile is a complex product for a variety of reasons. Firstly, it is the result of more than a hundred years of technical evolution, yet in many aspects resembles closely the cars that were sold at the beginning of the 21st century. Re- garding road safety, it is true that nowadays cars could be called safer than their predecessors, but they Figure 1. Many experts agree that the failure of Ford’s make allow drivers to travel a lot faster, and passengers are Edsel was a combination of bad marketing and deficient styling. involved in impacts with much higher kinetic ener- Photo source: Internet. gies to manage. Therefore, it can be argued that pre- sent automobiles are still not able to protect their oc- cupants in order to assure their survivability in the Lastly, every time an automobile company event of a road impact. launches a new model it spends a enormous amount Secondly, automobile users do not, in general, put of financial resources, in numbers ranging from few safety first. Over the years drivers proved to demand to several billion dollars, and there is little margin for cars that have grown faster and more powerful, and mistakes. Radical innovations are seldom understood there are very few potential owners which would re- or welcomed by mass consumers, and timing plays a fuse to drive the quickest Ferrari or Lamborghini if vital role in the success of any extreme modification they were able to pay for —and maintain— one of in a car —General Motors’ EV1 failed electric vehicle these fantasized automobiles. Then, there is the can be mentioned as an example of an audacious Peltzman effect which is the hypothesized tendency of launch made 15 years ahead of its time—. people to react to a safety regulation by increasing Before concluding this section, an appraisal about their risky behavior. For example, if some drivers an Eugene O’Neil’s play is presented. In “The Great with a high tolerance for risk who would not other- God Brown” the characters wear masks which serve wise wear a seatbelt respond to a seatbelt law by driv- two purposes: they help the characters hide and thus ing less safely, there will be more total accidents. protect their vulnerable inner selves while, at the Thus, in many cases, the safer the car, the reckless the same time, allowing them to project pleasing public driver, the fastest the impacts, the bigger the necessity images in an attempt to restore their confidence in to add safety devices, the heavier the cars, the higher themselves. Similarly, there are two key issues auto- the energies involved in road accidents, the more mobile generally hide behind their mask of freedom, dangerous the impacts, and so on. individuality and prosperity: damage to Earth’s eco- Thirdly, in the automobile world, beauty does system, and the tragedy of everyday road victims. matter. Many engineers may allege a style designer’s These two issues are way too complex to address in tyranny when arguing about who’s the one that makes this paper, yet it is the intention of this paper to zero the core decisions about the product. Nevertheless, in the fact that there are still some major improve- the truth is that there are a lot of good automobile ments to be introduced to enhance passenger protec- which were rejected by consumers simply because tion in the event of a road impact. And while for the they were not appealing enough. last few years many concept cars which focused on fossil fuel-consumption reduction were presented, the ZINI 2 last —and arguably one-time-only from a major car INJURY MECHANISMS manufacturer— concept car which pivoted on road safety (the Volvo SCC) was introduced as far behind “The current state of the field of biomechanics of as 2001. trauma can be compared to the state of the celestial mechanics before Kepler: it is composed of a multi- Bottom line, putting safety first in automobile tude of measurements and experimental data that design is no easy target.

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