Why can't Minnesotans zipper merge, and why do they get offended when others do it right?

Kate Thoma recently came upon a construction zone in Bloomington, and with traffic backed up in the left lane, she zoomed along in the unoccupied right lane until signs told her to move over.

She was zipper merging, but her efforts were thwarted by a left lane vigilante who would not let her in line.

"I'm certain he thought of me as rude and entitled, but I was just doing what my ninth-grade driver's ed teacher taught me," Thoma said.

Indeed, zipper merging is the law, but Thoma's experience prompted her to ask why Minnesotans can't zipper merge and why some motorists get all worked up when people do it. Two others sent in similar questions to Curious Minnesota, the newspaper's community-driven reporting project that invites readers to join the newsroom and ask the questions they want answered.

The Minnesota Department of Transportation in the early 2000s was the first in the nation to use the zipper merge to better manage traffic when a lane is closed in work zones. The concept is simple: Drivers remain in their lanes until a lane closes. Then, like we learned in kindergarten, drivers take turns falling in line.

"It's a great idea in theory, but theory is not how people always drive," said Dwight Hennessy, a traffic psychologist who teaches at Buffalo State College in New York. When people speed by in the open lane, he said, those waiting in line for a long time perceive them as being impatient rule breakers cutting in.

"It's perceived unfairness," said MnDOT work zone engineer Ken Johnson. But if drivers "use lanes to the merge point, fairness is taken care of."

Thoma has seen drivers intentionally blocking the open lane so nobody can pass.

That's a no-no, said Lt. Gordon Shank of the State Patrol, and a ticketable offense.

People view zipper merging as cutting in line, "and cutting in line is not 'Minnesota Nice,' " Thoma said. "It's not cutting in line. It's efficient."

Zipper merging in Minnesota is exclusively reserved for work zone bottlenecks, and not in situations such as when drivers use an "Exit Only" lane and then cut in at the last second instead of exiting.

"That is cheating. They are forcing themselves in," Johnson said.

But Minnesota remains committed and is continuing to teach the proper and polite way to merge. Through YouTube videos and a resource guide on its website, Johnson said the agency continues to educate drivers.

Thoma thinks a massive marketing campaign might help.

"I love the zipper merge," Thoma said. "If everyone did it, we'd all be better off."