Why didn't more people die when 35W fell?

It is no comfort to the loved ones of the 13 who appear to have died, or to those facing lifelong disability from the fall of the I-35W bridge, but the greatest puzzle of the disaster is that so many survived. What are Minnesotans made of?

How did so many survive?

It's hard to imagine anyone surviving a six-story drop into the Mississippi River.

But it's now apparent that the vast majority of those who were on the Interstate 35W bridge when it collapsed Wednesday escaped with relatively minor injuries.

Although the final death toll is still unknown, doctors and safety experts say that a combination of factors, from physics to shock absorbers, probably helped cushion the blow for those plunging from the bridge in their vehicles.

In general, they say, the cars and the bridge itself helped absorb some of the impact that would have killed someone free-falling from that height.

"I would say over two-thirds of the people walked away," said Dr. Marc Conterato, an emergency room physician at North Memorial Medical Center in Robbinsdale, who was at the site. "Believe me, the human body can absorb a lot of trauma."

As of Saturday, the death toll stood at five, and 24 people remained hospitalized, five in critical condition and four in serious. About 75 others were treated and released. About eight people are missing and presumed drowned.

As tragic as that is, it's a far cry from what some at the scene expected.

"I figured we'd probably have a couple of hundred injured, and 25 or 50 fatalities," said Dr. John Hick, an emergency doctor and disaster coordinator at Hennepin County Medical Center.

Many of those treated at hospitals had broken bones, fractures or back injuries from the vertical fall, according to physicians.

"I've certainly seen many worse injuries in car crashes," said Dr. Jeffrey Chipman, a trauma surgeon at the University of Minnesota Medical Center, Fairview.

In some cases, the vehicles dropped straight down on top of a portion of the bridge as it hit the water. That "would have created some kind of cushion when they landed," Chipman said.

James Kakalios, a physics professor at the University of Minnesota, agreed. "Some of them were able to ride parts of the expressway down," he said. "And that helped distribute the force and save the individual cars, as opposed to a car just falling 50 feet on its own."

Vehicle safety designs probably also played a role, said Lanny Berke, a mechanical engineer and safety specialist in Plymouth who is a frequent expert witness in accident cases.

"Let's start with the school bus," he said, referring to the bus carrying dozens of children. Because of federal safety rules, he said, it had an emergency door at the rear through which they could escape. "So the federally mandated design features for school buses saved those kids' lives," he said. "Because there's no way in hell they could have gotten out the front."

At the same time, he said, seat belts and airbags could have helped some survive, as well.

And the survivors had another thing going for them, the experts agree. "We were lucky," said Conterato. "We were actually in an area that was very well populated. People had relatively easy access to the area. Plus, we were relatively close to two large medical facilities, the university and Hennepin County. So we were able to put people on the scene relatively quickly.

I'm sure the cars were helpful, but the construction workers were standing on the bridge. They lost one person. Did they fly?

I suspect a lot of incidental bystanders took heroic risks to help people, risks that by rights should have killed them as well. Somehow even the rescuers survived. The rush hour group is also probably younger and more vigorous than a random population sample, Minnesotans are relatively healthy by national standards, the river is warm right now, and we obviously have a lot of competent swimmers ...