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When traffic is heavy and I’m in a lane that’s ending up ahead, should I try to merge where I am or should I move to the front of the line? My wife and I disagree on this. I was always taught to move to the front of the line and merge there, but she says that’s butting in. When she’s driving, she refuses to let in “the cheaters.” So who’s right here? – Kate, Toronto

Sometimes, when drivers cheat and cut to the front of the line, we all win.

When a lane ends and traffic is snarled, moving to the front of the line isn’t necessarily cheating – it’s called the late merge, or zipper merge.

“Research has shown that, if done properly, it can reduce congestion by 40 per cent,” said Kristine D’Arbelles, CAA spokeswoman, in an e-mail. “But it’s not meant to be one car racing to the front of a long line – drivers should be using both lanes equally and then alternating, like a zipper, to merge into one lane.”

Each car in the destination lane lets one car in from the lane that’s ending and then moves up. Then, the next car does the same thing. And so on.

Open this photo in gallery:

In this 2011 file photo, motorists merge from four lanes into one as they enter the Lions Gate Bridge to drive into Vancouver.DARRYL DYCK/The Canadian Press

Take your turn?

“How do people leave an airplane after it has landed? You take turns,” said Angelo DiCicco, director of operations at Young Drivers of Canada’s advanced driving centre. “That’s the concept of the zipper and also an all-way stop.”

Merging early is fine when traffic isn’t backed up and everybody is going the speed limit.

But the zipper works when a lane is ending – like in a construction zone – and traffic is so slow that you can’t merge early.

The zipper is supposed to prevent a bottleneck where drivers further from the front of the line hold up traffic as they wait for somebody to let them in.

When that’s happening at various places along the line, it can snag traffic.

“The zipper gets caught on the fly,” DiCicco said. “By merging near the end, everyone will get ahead.”

For instance, on Vancouver’s Lions Gate Bridge, multiple lanes merge, a little miraculously, into one at the front of the line without signs telling anybody exactly what to do.

In Missouri, the department of transportation encourages the zipper by not telling drivers too far in advance exactly which lane is closed for construction, CAA said.

When not to zip

CAA chapters in Alberta, Saskatchewan and Quebec have endorsed the zipper, D’Arbelles said.

But there are times when you shouldn’t be zippering.

If there’s an accident and there are emergency workers on the road, you want to get out of that lane that’s ending as soon as you safely can.

And it doesn’t mean you get to skip to the front of a long line of cars waiting in a dedicated turning lane and wait for somebody to let you in.

Doing that is stopping the flow of traffic – and enraging the drivers around you, said Ian Law, president and chief instructor of ILR Car Control School.

“It is illegal to stop and block a live lane of traffic,” Law said in an e-mail. “If a driver has missed their opportunity to merge into the lanes they need to exit, they should not stop in the live lane and hope someone lets them in.”

If the lane is for going straight, then cars have to go straight – although sometimes it might be easiest, and safest, just to let them in anyway.

“Maybe they’re from Lost Rubber Boot, Ontario, and they don’t know any better and their kids are in the car,” DiCicco said. “So you want to be magnanimous.”

And blocking them to teach them a lesson might backfire. If the car behind you lets them in, that cheater might aggressively ride your tail.

“The last time someone blocked you from merging, did you say to yourself, ‘Wow, I just learned a lesson – I’ll never do that again?’” Law said. “No, you just cursed and swore at them.”

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