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, because smokers had accepted any health risk arising from their habit. Even if that was true, it certainly wasn’t for others forced to breathe polluted air.

Secondhand smoke galvanized the anti-smoking movement. “You’re suddenly not talking about suicide,” said Robert Proctor, a history professor at Stanford University. “You’re talking about homicide.”

By the end of the 1990s, smoking was banned on domestic flights as well as across an expanding number of bars, restaurants, and workplaces. Tobacco use tumbled: In 2000, 25 percent of Americans said they smoked a cigarette during the prior week, down from 38 percent in 1983.

Secondhand smoke is a textbook example of a negative externality: a product’s costs that are paid by society instead of its users. It’s a framework that helped turn the public against tobacco, and it carries lessons for another product that is as ubiquitous today as cigarettes were 50 years ago. And like tobacco, its use can — and often does — kill innocent bystanders. I’m talking about oversized cars.

Over the last half-century, American sedans and station wagons have been replaced by increasingly enormous SUVs and pickup trucks that now comprise 80 percent of new car sales, a phenomenon known as car bloat. Much like secondhand smoke, driving a gigantic vehicle endangers those who never consented to the danger they face walking, biking, or sitting inside smaller cars. Although not widely known, car bloat’s harms are well-documented. Heavier vehicles can pulverize modest-sized ones, and tall front ends obscure a driver’s vision, putting pedestrians and cyclists at particular risk. Deaths among both groups recently hit 40-year highs in the US. The threat of hulking vehicles could even deter people from riding a bike or taking a stroll, a loss of public space akin to avoiding places shrouded in tobacco smoke.

Despite ample research demonstrating car bloat’s harms, American policymakers have done virtually nothing to counteract them. The political headwinds are powerful: Encouraged by carmaker ads depicting SUVs traversing rugged terrain, millions of Americans use oversized vehicles daily simply to get to an office, store, or school.

Convincing policymakers to regulate the size of automobiles would require a broad base of public support. The story of secondhand smoke shows how reformers could build it.

How the anti-smoking movement won over the public

Tobacco use was ubiquitous during the mid-20th century, even though scientists had started to link smoking and cancer before World War II. During the 1940s and 1950s, over 40 percent of Americans smoked cigarettes regularly, with most of them going through at least a pack a day. The cigarette industry was a political powerhouse, with many of its closest allies hailing from North Carolina, then home to more than a fourth of American tobacco farms.

In the postwar years, medical researchers produced a growing pile of studies concluding that tobacco damages smokers’ health. In 1964, the Office of the Surgeon General spurred a national conversation with a historic report linking smoking to lung cancer and heart disease. In 1967, the lawyer John Banzhaf, dubbed “the Ralph Nader of the tobacco industry,” cited that report when he convinced the Federal Communications Commission to require that TV networks broadcast anti-smoking ads that would counterbalance tobacco commercials.

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