By Ben Cohen | Photographs by Timothy Mulcare for WSJ

Over the past 250 years, America has produced the world's most valuable inventions.

The lightbulb. The internet. The telephone and the iPhone. Since the founding of the United States, we have built airplanes, refrigerators and Costco. We dreamed up the microchip and we gave the world chocolate-chip cookies.

But the greatest American innovation that you won't ever find on a list of America's innovations might just be one that you see every day.

It's an unsung idea that changed a nation and spread all over the world — and it was driven by one guy.

In the 1950s, around the time Jonas Salk cracked the polio vaccine, a metallurgist named John V. N. Dorr became the champion of a different lifesaver: a white line on the right side of the road.

For years, Dorr told anyone who would listen — and everyone who wouldn't — about his simple way of making highways safer. A line on the side of the road, he argued, would give drivers somewhere to aim their eyes at night other than oncoming headlights. It was both cheap and incredibly effective, which made it a brilliant investment. Over time, his revolutionary stripe of paint would reach billions of people and guide drivers across the planet.

To this day, you depend on it without knowing anything about it.

"I've never found anybody that knew about it," said Barbara McMillan, Dorr's great granddaughter.

It was also unknown to me until I wrote about another ingenious creation hiding in plain sight — the arrow that tells drivers which side of the car the gas tank is on — and a reader pointed me toward this overlooked innovation. Like that arrow on a dashboard, a line of paint on the road wasn't always there. Someone had to put it there.

In this case, it was someone who became so utterly obsessed with an obscure idea that he spent the final years of his life crusading for it.

John Van Nostrand Dorr was born in 1872, long before the Model T. He grew up in New Jersey, where he apprenticed under Thomas Edison. As a teenage lab assistant, Dorr learned a lesson from the master himself: try anything once.

After college, he tried going West and struck gold with mining equipment that helped separate solids from slurry. The success of machines like the Dorr classifier and Dorr thickener led to the Dorr Company and the Dorr Foundation, where he would make his most enduring mark on society.

To understand how a line of paint could be vital, it helps to go back in time and picture yourself behind the wheel.

Without edge lines, it was natural to hug the center line. It was also perilous. If drivers going in opposite directions were anchored to the same line, they could easily collide. The risk was especially high at night and in poor weather, when they were blinded by the glare of headlights. And if they couldn't stick to the center, they did the next best thing and swerved to the shoulder.

There was only one problem with veering to the side of the road: They didn't know where the side of the road was.

Dorr engineered a solution.

As I dug through historical documents — newspaper archives, foundation reports and budgets, a trove of his letters stashed in a museum — I wanted to know how Dorr became so passionate about such a peculiar cause.

By then, he was in his 80s and could have poured his philanthropic energy into trying anything once. So why this? Yes, he was idealistic and altruistic and earnestly committed to saving lives and making life better. He was also, according to his own brother, a terrible driver.

In family lore, his relatives told me, he even managed to drive off the road while driving his granddaughter to the hospital to have a baby.

As it happens, there were lots of terrible drivers on the road — and in the ditches beside them. He wasn't even the only member of his family in need of an edge line. Dorr was inspired by his wife, Nell, a renowned photographer, who was tired of riding shotgun and craning her neck out the window to see where the asphalt ended. She convinced him there had to be another way.

Once he discovered it, Dorr proposed the line to his state's highway commissioner in 1952. The man in charge of Connecticut's roads told him to get lost.

"When I first suggested it," Dorr later wrote, "it was turned down completely."

The next time he suggested it, he wrote to the Westport Town Crier newspaper in 1953 and offered to pay for "a demonstration test of a few miles."

This time, he got a more welcoming response.

"Dr. Dorr's suggestion," the paper wrote in an editorial, "is a dandy."

Before long, Connecticut was testing his dandy idea on a few miles of the Merritt Parkway between Greenwich and Stamford. The study found that Dorr's line nudged cars away from the center line, into the middle of their lanes, and narrowed the speed gap between day and night. In other words, the study found scientific evidence that a single line could dramatically alter human behavior.

It was soon confirmed by a similar experiment on a section of highway in New York that had come to be known as "Death Valley." In the five months before the arrival of Dorr's line, there were 40 accidents in this treacherous corridor. Over the next five months, there were only 14.

Now that he had data, Dorr was relentless about getting it in the hands of people who could slap the line on more roads.

He sent monthly progress memos to a mailing list that included the highway commissioners of all 48 states. He pitched stories to publications with names like Better Roads and Traffic Engineering. He wrote letters to anyone who could make his idea a reality — governors, a Broadway star, former President Herbert Hoover.

Others may have tinkered with edge lines before Dorr, but he used his influence to make them part of everyday life.

Like sticky notes, rolling suitcases and the yellow first-down line in football, the solid white line on highways now sounds obvious. It wasn't. In fact, it once sounded radical.

When he began his campaign, the agency overseeing the safety of America's roads specifically warned against edge lines, fearing they would confuse drivers. This meant he was lobbying states to spend money on something that authorities said they didn't need — and something they dismissed as too expensive. The cost was $50 per mile per line, which government officials considered a waste of $50. Dorr considered it a bargain.

"Paint," wrote the New York Daily Mirror, "is cheaper than blood."

Despite those economics, the bureaucrats remained skeptical. Dorr kept trying to win them over and kept losing.

"We have not found any locations," Ohio's highway director told him, "where we believe edge-marking would yield sufficient value to warrant its extensive use."

It would soon be used quite extensively in Ohio, which became a Petri dish for Dorr's line. To measure its value, the state ran a controlled experiment and determined whether roads were striped or left unmarked by flipping a coin. The results were as unequivocal as heads and tails. Over the next year, the lined highways reported significantly fewer crashes and a 37% reduction in fatalities and injuries.

With those numbers, it was only a matter of time before the line went from discouraged to permitted to everywhere.

In less than a decade, Dorr's line was so popular that people wondered how they ever lived without it.

"The public is demanding it," a Bureau of Public Roads official declared in 1958. "Everywhere drivers are saying: 'This is the finest thing we've ever seen.'"

As soon as they saw it, they couldn't unsee it. Before he died in 1962, Dorr watched his idea stretch across the country, around the world — and all the way to his front door.

One morning, he stepped outside and there it was: a Connecticut highway department truck, painting a line down the side of the road.