Nearly 10 years ago, something new — the “zipper merge” — was discussed in a “Safety on the Roads” column. Over the summer, the state Department of Transportation has implemented a zipper merge on I-490 in Rochester, where new bridges are being constructed over the Erie Canal and Kreag Road. It’s a $60.8 million project, and the first time the zipper merge has been used in the state.

Normally, when a lane is closed for a prolonged period on a multiple-lane interstate highway, drivers are warned that a particular lane is closed a mile ahead. The expected outcome is that drivers will move their vehicle into the open lane well before the actual lane closure. Normally this method works well, depending on traffic volume and speed.

A zipper merge works much differently. It is designed for drivers to continue in all available lanes until the merge point is reached where the lanes taper. At the merge point, vehicles from each lane are to take turns entering the through lane, much like the teeth of a zipper.

Each method of merging has its pluses and minuses. The early merge works reasonably well if traffic is very light, and highway speeds can be relatively maintained up to and through the construction zone. But, because any lane closure reduces the capacity of the highway, traffic jams often occur. Sometimes traffic backs up beyond the signs that give drivers advance warning of a lane closure.

The biggest negative with the zipper merge is that most drivers are not familiar with it and how it should work. It is, after all, new to drivers — not just in New York.

Studies have shown a late or zipper merge actually increases capacity through the construction zone by about 15% and simultaneously reduces the time it takes to get through the construction zone. This is predicated on drivers understanding of the zipper merge and performing it correctly.

I am very familiar with this method of merging, having driven through zipper merges in Montreal for several years as Quebec reconstructed the Turcot interchange on Autoroutes 20, 15 and 720, the busiest interchange in the province. It carries 300,000 vehicles a day, including 30,000 trucks.

Although there is always a delay, the late-merge scenario keeps queues shorter, albeit traffic moving at a slow pace, and, at the merge point, all drivers alternate their turn. In my experience, there is no bullying or forcing one’s way ahead of the alternating vehicles.

In the Rochester project, the first sign states “STAY IN LANE TO MERGE POINT.” This is followed by warning signs stating “ROAD WORK XX MILE,” followed by “RIGHT (LEFT) LANE CLOSED XX MILE,” another sign showing the right (left) lane closed ahead, and lastly by a sign at the merge point that reads “MERGE HERE TAKE TURNS.”

If you drive a lot, at some point you will encounter a zipper merge. When you do, don’t hesitate to continue in either lane right up until you reach the merge point.