A Tech Opinion on Volvo & Safety


Subject:          Volvo Safety
   Date:          Mon, 23 Jun 2003 23:11:26 -0400
   From:         Eric Dubac
     To:          ozbrick
 
 
 

Re: Volvo vs. other cars, in particular American cars.
 
All things being equal, heavier is better, but all things are not equal when comparing a Volvo to any American car.
 
In a nut shell, the laws of momentum provide a general overview of how weight affects crash performance, the equation is:
 
    (M1 x V1) + (M2 x V2) = (Mtotal x Vtotal)
 
where
 
    M1 = Mass of the first car
    V1 = Velocity of the first car
    M2 = Mass of the second car
    V2 = Velocity of the second car
    Mtotal = Combined mass of both cars
    Vtotal = Combined velocity of both cars after crashing into each other
 
You can examine different scenarios by plugging in different Mass (Weight) and Velocity (Speed) values for the cars with one car having a positive
(+) Velocity and the other car having a negative (-) Velocity if they are headed towards a head on crash. The key result is the difference between the
Velocity of the car in question before the crash (i.e. V1 or V2) and the velocity of the cars after the crash (Vtotal).  The difference is called the delta V
which is the change in velocity that the occupants of a car go through, a VERY CRITICAL FACTOR WHEN PREDICTING THE LIKELIHOOD OF
INJURY. If you understand the equation, then you can experiment with different scenarios, but there is a simple rule of thumb which is:
 
The change in velocity that the occupants of a car undergo is directly proportional to the weights of the vehicles. If one car weighs twice as much as
the other, then the occupants of that car will undergo half the change in velocity experienced by the occupants of the other car.
 
This would lead to the conclusion that all things being equal except the weights of the cars, bigger is clearly better, but things are not so simple.
 
There are two important factors that will determine if the passenger survives a particular change in velocity, or turns into jello.
 
The first factor is the rate of change of velocity. If you do not have your seat belt on and smash into the windshield and dash board (even in a car with
airbags) you will experience a very rapid change in velocity and will again turn to jello. If you are wearing a seatbelt and decelerate as the car
crumples over a longer period of time, the peak forces on your body will not be as high, and you just may walk away un-injured.
 
The second factor is how the deceleration forces are applier to your body. If they are concentrated as in impacting the windshield or dash board,
there again will be the instant jello. If the forces are spread over the surface area of the seat belt and much larger area of an air bag, then you have a
much better chance of being un-injured.
 
Volvo, in particular, has done a very good job of dealing with the first and second factors. They have well designed seatbelts and airbag systems
that decelerate the occupant with the vehicle and spread out the forces on the occupant. It would be too tedious to go into the details here but Volvo
does a better than usual job.
 
The other un-seen difference between Volvo and American manufacturers, is the approach to building cars that is not readily obvious to anyone but
an engineer.  To put it simply, Volvo actually wants to build a safe car, and in my opinion, actually cares if someone gets hurt. The American car
manufacturers are primarily driven by $$$. Point in case, look at some older Volvos and compare them to American cars of the same year. You will
find lap and shoulder belts, and head restraints, in all three rear seat locations appearing in Volvos many years before they show up in the American
cars. These safety features are critical to your survival in an accident, but since they do not have the high profile marketability that air bags do, the
American manufacturers have not adopted them because in my opinion they cost more to put in the cars than they give in return in making the cars
marketable. To harp on this a bit more, look at the rear head restraint in a Volvo, it is large and concave to cradle your head if you are hit from
behind.  Now look at a head restraint in an American car, they almost always do not have a concave shape to cradle your head, and they are not tall
enough (tall enough is higher than your head) to properly support your head.
 
If all of the rambling you just read did not mean much, then let me say this: As a Mechanical Engineer, Fireman, and Emergency Medical Services
provider, my family rides in a Volvo 850 wagon.  Given all of the considerations, it is in my opinion the best overall choice for safety, not only
because of the obvious safety features that are touted by the people who only want to sell a car to make money, but the un-seen safety features that
are built into cars by people who actually want to make money and have some sense of ethics.
 
In closing I would like to say that based on what I have seen when responding to ten years of car accidents, do the following:
 
    -Air bag or not, wear your seat belt ALL OF THE TIME
    -Put all children in the appropriate car or booster seat for their height and weight
    -Put children in the back seat (the middle of the back seat is the best)
    -Go to your local police station, fire department or EMS provider and ask about having your car seat inspected for
      proper installation. Many agencies now have personnel trained in the proper installation of car seats who will be happy to
      check yours. Some surveys have shown that the MAJORITY OF CAR SEATS ARE IMPROPERLY INSTALLED.
    -DO NOT SPEED, at 78 mph the forces in an accident are twice as great as would be at 55 mph.
    -Slow down in the rain
    -Do Not Drive Drowsy, it is as bad as driving Drunk
    -Follow at a safe distance
    -Turn on your headlights all of the time, some studies show a 30% reduction in multi-vehicle accidents pertaining to cars with
      Day Time Running Lights (the headlights automatically go on with the engine), and if you do not want to keep turning on your
      lights whenever you get in the car, have a Daytime Running Light unit installed on your car, it will automatically turn on and off
      the lights for you. Having your headlights on during the day has a substantial enough reduction in accident rates that daytime
      running lights are required by law in Canada and Sweden.
    -I know they are expensive, but get 4 studded snow tires on whatever you drive, even if it is 4WD, they could save your life.
 
I know that I have rambled on here, but I feel that this stuff is important.
 
Happy Motoring!
 
 
 



 
 

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