Driving through a cone zone? Merge like a zip — experts insist it’s OK

Nobody likes that jerk who races to the front of a traffic lane that’s been blocked for construction and then merges at the last second.

But that jerk might be doing it right, according to traffic studies.

While the so-called “zipper merge” may not be new — some state transportation departments have promoted it in recent years — AAA mid-Atlantic is again asking drivers to use the strategy as construction zones pop up on area roadways.

With major transportation projects in Northern Virginia, Maryland and D.C., “the whole landscape is one big cone zone,” said John Townsend, AAA Mid-Atlantic’s manager of public and government affairs. “No matter where you travel, you will encounter a work zone.”

Townsend said drivers can benefit from the merging strategy, in which drivers approaching construction drive right up to the point where a barrier narrows the roadway into the neighboring lane, and then merge — one at a time — by taking turns.

Traffic engineers liken it to the action of when the individual teeth of a zipper are joined, hence the term “zipper merge.”

WTOP Traffic reporter Dave Dildine said the method is sound — in theory.

“In most circumstances, the zipper merge is the most efficient use of the available driving surface,” he said, but it doesn’t take into account what happens in practice.

When drivers shift lanes to accommodate the work zone see others sliding into the lane they just vacated, it can really generate anger. “Not all drivers can cope with seeing other drivers zip right past them to the front of the queue,” said Dildine.

Depending on the roadway speeds, it’s generally best to have all drivers in all lanes move to the front of the queue and merge at that point, said Kara Kockelman, a transportation engineering professor at the University of Texas at Austin. But it’s often not popular.

When all drivers merge early and make a single lane, leaving the lane that is being narrowed vacant, they’re not making the best use of road capacity, Kockelman said, “and yet, a lot of people do it because they think they’re behaving properly.”

The problem with the zipper merge, Townsend concedes, is that everyone has to buy in.

“Everyone has to cooperate,” she said.

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