Prof: Car weight doesn't equal safety


Dad's advice to buy a heavier car for safety's sake may not be as good as he thought, a University of Michigan physicist says.

U-M physicist Marc Ross and Tom Wenzel, a research scientist at Lawrence Berkeley National Laboratory, say their research indicates vehicle quality is a better predictor of safety than weight.


"It turns out that relatively inexpensive light cars do tend to be unsafe but more expensive light cars are much safer and are as safe as heavier cars and SUV (sports utility vehicle) models," Ross said.

"In any event, the argument that lowering the weight of cars to achieve high fuel economy has resulted in excess deaths is unfounded. If designers pay careful attention to vehicle design, smaller cars can be, and indeed have been, made as safe as larger ones."

Much of the argument over whether to force automakers to increase mileage has centered on safety, with carmakers arguing forcing Americans to give up their sport-utility vehicles in favor of smaller, lighter, more fuel-efficient models would lead to an increase in traffic fatalities.


"We set out to see whether that risk is real, whether SUVs really are safer than cars," Ross said. "The answer, by and large, is no."

However, the Insurance Institute for Highway Safety disagrees.

"No matter what you do, you cannot repeal the laws of physics," institute spokesman Russ Rader said. "A larger, heavier vehicle is always going to be safer than a smaller, lighter vehicle. If you're looking at small cars vs. larger cars, small cars have twice as many occupant deaths as large cars."

Rader said statistics indicate death rates go down as vehicle weight goes up, especially in single- and two-vehicle crashes. He noted, however, SUVs have a higher rollover risk and are disproportionately involved in single vehicle crashes.

Ross said the safety question depends how categories are divvied up.

"Analyzing statistical things is sort of funny," Ross said. "If you choose categories so you get cheap cars in your category, then the death rates go up. What we found is that the price of a car is a much better predictor of risk in traffic accidents than the weight of the car."

Ross and Wenzel said their research indicates SUVs are no safer for their drivers than cars and that popular midsize cars, minivans and import luxury cars have the safest records. SUVs are about as risky as the average midsize or large car and no safer than many compact and subcompact models based on the number of deaths per year per million miles.


In considering other factors as well, pickups are ranked as the most dangerous vehicles.

"Clearly the characteristics of the drivers of certain types of vehicles also have a strong effect on their safety," Ross said. "However, it is not clear exactly what that effect is, and the age and sex of drivers do not fully explain these results."

The researchers examined such factors as new car price, used car price, Consumer Reports safety ratings and country of origin.

"Safety is a challenging concept," Ross said. "It includes the design of the car itself, driver demographics and behavior, the kinds of roads, the time of day -- a whole host of factors. What we need to do is move away from the idea that bigger and heavier vehicles are automatically safer."

Ross and Wenzel plan to present their research Tuesday at Lawrence Berkeley's Washington office.

Latest Headlines