Highway drivers should be mindful of the zipper
Traffic control experts say the ‘late merge’ is the easiest, safest way to merge two lanes, despite our emotions
It’s the burr in the saddle for drivers all across Niagara this summer — lane closures and forced mergers in construction zones.
When two busy highway lanes converge into one, experts say there is a right way to handle it.
And the right way doesn’t include refusing to let vehicles merge into your lane when theirs has ended.
It also doesn’t include straddling the centre line so drivers losing their lane can’t get ahead and butt into your line.
The right way, they say, is known as the zipper merge — the late merge — whereby drivers in the lane that’s closing stay there until the very end.
Then like a closing zipper they merge one by one with vehicles in the continuing lane.
The evidence is in — in high-volume traffic it works, says Brian Malone, vicepresident of transportation for the engineering and urban planning firm CIMA+ in Burlington.
The idea, he says, is that “we’re all in this together — OK you go, then I’ll go.
“Then you do get, or should get, a relatively even balance between the merging that takes place.”
The other way — merging early — might feel like the polite way, but it can force drivers in both lanes to slow down and lead to lane changes and traffic flow issues.
It might go against the grain for drivers who don’t want to let the other guy butt in, but studies show the zipper merge is the fastest way to move traffic where lanes are reduced.
Lineups are shorter and there are fewer collisions compared to having drivers merge before their lane ends.
“You maximize the available space on the road for storage, have people ready to make a merge, and then they merge at the last moment,” says Malone.
But merging traffic can be a sore point for drivers who don’t want to let the other vehicle in.
In extreme cases it can turn tragic, as happened in 2013 in Niagara Falls when a pickup truck driver on Highway 420 refused to let another vehicle merge to reach an exit.
Eventually both vehicles were speeding and their wheels touched, court was told. The second driver lost control of her car and was killed when it struck a light standard.
After pleading guilty to dangerous driving causing death, the truck driver was sentenced to 18 months in jail and barred from driving for 10 years.
In light traffic, early merging works fine because there are obvious gaps between vehicles.
In 2016, a study by North Carolina State University found “a new traffic treatment called a ‘zipper merge’ has the potential to reduce traffic backups by as much as 50 per cent in areas where there are lane reductions, or dropoffs.”
In it, state traffic engineer Kevin Lacy acknowledges it requires a change of thinking, but adds, “with a little extra courtesy we could greatly reduce the length of traffic jams, decrease travel times and increase safety.”
On its website, CAA notes the zipper merge “is antithetical to Canadians’ usual politeness: zooming up a clear line before a construction zone and attempting to merge late … rather than merging early into the through lane at the first sign of construction.” Yet it works, the agency reports. Says Malone, “While it may not work perfectly — you get people who either refuse to or fail to understand they need to yield to alternate between each of the lanes — when it’s relatively congested and speeds are relatively low it actually works fairly well, studies show.”