Gigantic SUVs are a public health threat. Why don’t we treat them like one?

With an annual toll of 40,000 American lives, the deadliness of secondhand smoke is now common knowledge. But it was only a few decades ago that puffing on a cigarette was defended as an act that affected only the smoker.

In the 1980s, researchers for the first time demonstrated that smoking can kill people who never themselves lit a cigarette. Those findings undercut tobacco industry claims that smoking need not be restricted...