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What is the Safest Car to Buy?
Published: October 24, 2008
Author: David Easton
As both a Registered Professional Engineer and a trial attorney, I have worked on a variety of automobile accident cases. A large number of these cases involve allegations that the automobile manufacturer failed to provide protection from otherwise foreseeable hazards. Such hazards include:
- Post-crash fires (gas tank in the collapse zone)
- Instability leading to rollover (track width too narrow for center of gravity height)
- Vehicle structure intruding into the occupant space during impact, causing an enhanced injury (crash-worthiness)
- Vehicle structure placed in the belted occupant's ride down space, leading to a second impact and enhanced injury (second collision)
- Failure of the vehicle's seat belt and shoulder harness to hold the occupant in the protect zone, leading to extension and/or ejection (restraint failure)
Because of my experience with automobile accident cases, I often am asked: What is the safest car to buy?
The answer depends on the hazard. For instance, if you knew you were going to be involved in a collision with a heavy truck, a bigger vehicle is always better. If you could avoid an impact with the same heavy truck through maneuver, then stability is the best design.
In the past, I answered the "safest car" question by saying that the safest car for you is the car that guards against the most likely hazard in your use of the vehicle. The introduction of pretensioner-type seat belts has changed that.
What are pretensioner-type seat belts? A pretensioner-type seat belt is a seat belt, shoulder harness, sensor and explosive charge system that tightens the seat belt and shoulder harness under certain conditions. The seat belt and shoulder harness look the same as they have looked like for years - nothing new there, The sensor and explosive charge system are new and unique to pretensioner-type seat belts.
Seat belt sensors have been around for years. The older designs rely on two redundant methods to lock the seat belt and shoulder harness.
The first method utilizes a lead pendulum which moves when it experiences acceleration in any direction. Acceleration can be both positive and negative. When you increase the speed of your car, positive acceleration occurs. When you step on the breaks, decreasing the speed of your car, negative acceleration occurs. If you are involved in an accident where you hit the car in front of you, negative acceleration occurs. If your car is hit from behind, positive acceleration occurs. When the pendulum experiences either positive or negative acceleration, it moves and interferes with the gear system, locking the seat belt and shoulder harness. If you were leaning forward at the time that the acceleration occurred, the seal belt and shoulder harness would lock even if there was extension from leaning forward. This feature was less than ideal. The auto industry originally valued seat belt comfort, to increase use, over its ability to lock at a precise point.
The second redundant method of locking the seat belt and shoulder harness during an accident involved the rate of extension of the seatbelt webbing from the reel upon which the webbing was wound. If that rate was high, the reel would be spinning, and centrifugal force would cause extension of small hooks on the perimeter of the reel. Again, these hooks, when extended, interfered with the gear system, locking the seat belt and shoulder harness. This second method of sensing required the seat belt reel to rotate and, as a result, some amount of web extension occurred before the seat belt and shoulder harness locked.
The pretensioner seat belt design lessens these problems. The pretensioner seat belt design uses an electronic sensor instead of the mechanical design previously described. In addition to sensing positive and negative accelerations, the electronic sensor senses roll, yaw and pitch, and further distinguish between the minor and major levels of each. Along with locking the seat belt, the electronic sensor can close the windows before an impact, lock the doors, shut off the ignition and call for help. Most importantly, the electronic sensor activates the electronic charge.
What does the explosive charge system do? It moves the piston and cylinder to effectively pull the seat belt webbing, including the seat belt and its shoulder harness, tight around the occupant's body. By introducing tension in the seat belt webbing before an impact or a rollover occurs, the user is moved to the location in the vehicle that best protects him or her.
Regardless of whether the hazard is front impact, rear impact or rollover, the pretensioner puts a car's occupant in the safest position possible, tightly secured by the tension, and remains locked until the sensor senses the hazard is over. For these reasons, pretensioners are very effective in reducing injury during automobile accidents.
What is the safest car to buy? The safest car for you is the car that guards against the most likely hazard in your use of the vehicle, and that has a pretensioner-type seat belt. A pretensioner seat belt and electronic sensor provide the greatest level of safety for its occupants.
Not all cars have pretensioners, so check before you buy. Some models of Mercedes Benz have had them since 1992. BMW, Volvo, Saab and Volkswagon have had pretensioner belts since 1998. GM, Ford and Chrysler have offered them on select models since 2004. An Internet search for "2007 Chevrolet Tahoe safety features" should tell you if pretensioners are part of the safety features.
Bottom line: Ask if a car has pretensioner seat belts before you buy it.
Mr. Easton is a partner at the Wisconsin law firm of Axley Brynelson, LLP and a Registrated Professional Engineer. His practice focus on personal injury law, technical litigation, industrial injuries law and aviation accidents law. For more information, please contact Mr. Easton at deaston@axley.com or 608.283.6713.
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