Q: You say that seat belts save lives, but have you considered that those involved in a fatal crash don’t need extensive medical care? It’s the non-fatalities through use of seat belts that often require extensive and costly medical services.

A: It sounds like you’re suggesting that the reason we shouldn’t use seat belts is because it’s cheaper to have people die than to treat them.

I see two possibilities for people who think like this: They who don’t care about other humans and people who don’t care about physics or biology. I want to assume you care about other people, so we’ll focus on your neglected science lessons.

The human body has a limit on how much force it can sustain in a crash. The National Highway Traffic Safety Administration figures that 60G’s (60 times the force of gravity) for three milliseconds results in a high likelihood of serious injury or death. Probably death.

G-force doesn’t mean much without context. What does it take to generate the kind of G-force that causes severe injuries or death? There are a lot of ways to crash, and they all have different effects on the body, so I’m going to simplify things and just consider a head-on crash into a fixed object, like a wall or a full-grown maple tree.

When you crash into something, you don’t stop immediately. There’s a fraction of a second when the crushing happens (to your car, not you hopefully). That’s the time it takes to come to a complete stop. Without a seat belt, the stopping time is about the same for your body and your car. You fly through the space between your seat and your steering wheel/dashboard/windshield at the speed you were driving, and that stuff stops you. When you wear a seat belt, that time is extended for your body, as your seatbelt slows the time it takes you to travel from your sitting position to the steering wheel.

That tiny bit of time has a huge effect on the force you experience. If you drive straight into a concrete wall at 35 mph while wearing your seat belt, you will experience about 40G’s. It’ll hurt, but you’ll likely survive. We know this partly due to research done in the 1940s when Dr. John Stapp of the Air Force built a rocket-powered sled to test the effects of G-force on the body.

Stapp was his own test subject; in his 16 runs he suffered multiple injuries, including broken bones, and on his most dramatic (and final) run when he decelerated at 46 G’s, temporary blindness. Take away the seat belt, and that same crash generates, according to nerds who make physics calculators, about 200 Gs. This is why your suggestion that seat belt use increases medical costs is severely flawed. Eliminating seat belts just shifts serious injuries (and costly medical services) to lower-speed crashes.

You’re also reducing the speed at which people are likely to die. I guess you’re right that there won’t be medical costs for the people who die, but many of those low-speed crashes that buckled drivers walk away from would become serious injury crashes. The end result of your thought experiment is a probable increase in serious injury crashes and a dramatic increase in fatalities.

The takeaway here, besides avoiding roads with concrete walls in them, is that seat belts save lives; more lives than any other vehicle technology. 94% percent of us agree and wear our seat belts.

Doug Dahl writes a weekly column for this newspaper. He is with the state Traffic Safety Commission.