MADRID (MarketWatch) — Most of America is making a living on eighteen wheels.

That’s what research conducted by National Public Radio, which recently mapped out the most common jobs in each U.S. state, has revealed. And as of last year, in a majority of states, truck driving is the most popular job category. The NPR interactive map shows how the landscape for employment has changed across the nation from 1978, when farmers, secretaries and machine operators ruled the roost, to 2014, when truck driving emerged as No. 1.

By 1996, in fact, truck driving had become the most popular occupation across 29 states. The NPR map shows that while in the late 1970s, secretarial work was far more common than truck driving, the typing pool dwindled by the mid-1990s. Here’s NPR’s full examination of the data.

The Bureau of Labor Statistics has predicted that employment of truck drivers will grow 11% from 2012 to 2022. “Job prospects for heavy and tractor-trailer truck drivers with the proper training are projected to be favorable,” said the BLS. But before you sign up for truck-driving classes, read the rest of that paragraph: “Because of truck drivers’ difficult lifestyle and time spent away from home, many companies have trouble finding and retaining qualified long-haul drivers.”

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In four states where truck driving is not the most common job, software developer is: in Washington state (zero surprise), Virginia, Utah and Colorado. Primary-school teacher was the most common job in 2014 in six states.

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The most common job category in New York, where the secretary was long ascendant, were nursing aides, orderlies and attendants last year. A recent Glassdoor survey of the 25 best jobs in America, based on earnings potential, career opportunities and number of job openings, ranked physician assistant No. 1.

And if you’ve suspected most of the population in D.C. is composed of lawyers, then the map proves you’ve been on the right track. That lawyering is tops in only one state may gibe with the recent observation that, along with doctors, professors and stockbrokers, lawyers have lost some cachet of late.

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As for methodology, NPR used Census Bureau data, tossing out the too-vague categories of “managers not elsewhere classified” and “salespersons not elsewhere classified.” The reason truck driving is so heavily represented, they say, is that a “worker in China can’t drive a truck in Ohio, and machines can’t drive cars” — yet.

NPR also notes that when the government categorizes jobs, it lumps together truck drivers and delivery people, making for an extra-large category. The dwindling secretary category is explained in large part by the rise of personal computers, which have laid waste to much of what that role used to encompass.

If you saw the movie “Interstellar,” then the fading occupation of farming just might alarm you a bit. Only North and South Dakota are still waving the flags of that occupation as their most popular.