Over the past few decades, the annual death rate in America has declined dramatically, but the leading causes of death have remained the same. Heart disease kills the most people, and then cancer. Strokes kill a smaller portion of us, but they're often up there, too. After that, often, it's accidents that kill people—especially younger people. According to the Centers for Disease Control and Prevention, "injuries are the leading cause of death for people ages 1-44." And the largest single cause of those injuries are car accidents.
But, really, it's incredible that more people don't die in motor vehicles (which are, essentially, giant chunks of metal hurtling through space, on the enormous strength of combustion). In 2010, the death rate from motor vehicle-related injuries was about two-fifths of what it was in the 1970s, when it peaked. In other words, safety standards worked. But making them work required a very specialized piece of technology—the "anthropomorphic test device," more popularly known as the crash-test dummy.
The first of these were designed for America's aerospace program, which wanted to test jet-ejection seats. The car industry, meanwhile, was testing its first safety devices on cadavers, which, as The New York Times later wrote—quite delicately!—"lacked the durability required for repeated trials." There were other problems with this method, besides the obvious ones: Cadavers do not come in standard shapes, and in crashes they don't behave like the bodies of living people. Pigs were also early test subjects.