As a mechanical engineering professor at Cal Poly, I was aggrieved to read about the auto accident in The Tribune (Oct. 11).
The night before I had written a short semi-technical paper on energy dissipation in vehicular collisions. Much of what I’d figured out and explained in that paper seemed to have been played out in this accident. Driving fast in a heavy, rigid vehicle endangers everybody else on the highway driving normal, nonstiff cars.
Normal cars are designed to crumple in a crash. Kinetic energy, the energy of motion, is dissipated by this crushing. And that is what is needed in a collision is to get rid of the kinetic energy that the involved cars bring into a crash.
Pickups and SUVs contribute inordinately to the energy brought into a collision because of their weight. If such a vehicle is speeding, as seems to have been the case in this accident, that has a multiplier effect on the kinetic energy brought into the crash. Yet an SUV or pickup contributes little to the dissipation of energy because it is a very stiff vehicle, so it doesn’t deform much. This is evident in the picture on the front page. The Camry is crushed up into its passenger compartment, but the structure of the Tundra is still intact.
Perhaps it is unwitting, but a driver of an SUV or pickup in a collision with a normal car depends on that car to absorb and dissipate the energy of the crash. The normal car is crushed more than it would be if it crashed into another, nonrigid car. In a collision between two normal cars, both are crushed and share the kinetic energy dissipation. But each is not crushed as much.
I have heard many SUV drivers say that they buy such a vehicle because of its safety features. Yes, it is safer for its occupants. But it buys this safety by laying the energy dissipation burden on other vehicles and endangering those drivers. This point is borne out in this tragic accident. SUVs and pickups are truly killer vehicles.
Frank Owen lives in San Luis Obispo.
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