PennDOT Trying Approach To Merging That's New To The Area

Sep 26, 2017

Traffic merging on North Atherton Street in advance of construction work in State College.

It’s a weekday morning on North Atherton Street in State College. For David Reitter, a Penn State faculty member, and others commuting on that road, it usually means one thing.

“Just like everybody else, I get stuck in traffic.”

A gas line relocation project means torn up roads on North Atherton in advance of a Pennsylvania Department of Transportation roadway project. Drivers there dutifully merge from two lanes into one, sometimes well in advance of road work.

Many people use North Atherton to commute to work, and the situation can be dismaying by State College traffic standards.

“We’ve got literally hundreds of cars and buses waiting to get to the Atherton, Park Avenue intersection," Reitter said. "Oh my, I don’t even want to get into this.”

That’s Reitter, taking stock of the situation. An assistant professor who studies how people make decisions, Reitter is one of those who hope more drivers will use both lanes for as long as possible, rather than merging far ahead of a construction site. He points to the research backing that idea.

“We’ve got that convention. We try to merge early. We try to wait in line and take our turn. And when there’s already a long line of cars waiting, we queue up at the end," Reitter said. "The problem is, it’s a bad idea.

“If there’s road to be used, use it and merge late.”

As it turns out, PennDOT has started using that approach to merging, and plans to use it more.  

“It’s called the late merge concept. And, basically, that means that both lanes are open for motorists up to the actual merger or closing point," said Erik Brown, district traffic engineer with PennDOT. His district includes nine counties in central and northcentral Pennsylvania.

With the late merge or zipper method, large signs on both sides of the road tell drivers to use both lanes up to the merge point. At the merge point, a sign tells drivers to “merge here” and “take your turn.”

Brown points to research on the late merge or zipper method.

“They found out that allowing motorists to use both lanes right up to the merge point – it increases capacity by 20 percent. They also found out that there was a 50 percent reduction in queues, meaning stacked traffic waiting to get through the construction zone.”

That’s important because if drivers get stuck in a single long line waiting for construction, that queuing can lead to stopped traffic before the project, which can contribute to rear-end collisions.

PennDOT did try the late merge another time in the district — on South Atherton Street— with mixed results. Many drivers merged earlier than they needed to, leaving one lane wide open except for the occasional motorist who zipped down it to the merge point.

“Really, I think it’s just a familiarity, and motorists are always so used to the old concept of just the typical lane closure and just trying to get over into that open lane as soon as possible. This late merge concept is something new to a lot of motorists, so I think it will get better with time.”

Drivers who missed the chance to try late merging on South Atherton Street will have another chance next year. Brown said plans are to use the late merge approach on more projects. Look for it in the fall 2018 on a resurfacing project on Interstate 99 from Valley Vista to Fox Hollow Road.

I’m Anne Danahy, WPSU.