RALEIGH – The N.C. Department of Transportation recently introduced new technology in several busy work zones to improve safety, ease congestion and reduce backups when two lanes of traffic merge into one lane.
The Dynamic Zipper Merge relies on a series of speed sensors set up on the side of the highway several miles before drivers must merge into a single lane in work zones. The sensors gather data about traffic congestion and then feed the data to a message board that changes the message drivers see based on the traffic patterns approaching the work zone. For instance, the messages may indicate “Slow Traffic 1 Mile” or “Stopped Traffic 2 Miles.”
When congestion is heavy at an Interstate 77 North project in Yadkin County, for instance, signs using the new system display “Merge Here” and “Take Turns” at the start of the work zone.
As its name suggests, this type of merge is intended to work like a zipper. By taking turns at the merge point, drivers experience smoother merging conditions, which reduces traffic backups.
“The use of these messages in heavy traffic reduces the confusion between drivers who think they should merge early versus those who want to use the open lanes for as long as possible,” said Kevin Lacy, the department’s chief traffic engineer. “This helps remove aggressive driving behavior.”
The Dynamic Zipper Merge has already worked well to reduce congestion on North Carolina interstates where it was introduced this spring. When construction closed one of two lanes at the I-77 North project in Yadkin County in March, the line of backed-up traffic reached 8 miles. In May, after the Dynamic Zipper Merge system was installed, the maximum backup was reduced to about 2 miles.
The system also was installed in April ahead of these two work zones in Davie County near Winston-Salem: Interstate 40 East and I-40 West. A fourth system is scheduled to be installed next week for the other direction (I-77 South) where the concrete roadway is being replaced in Yadkin County.
Here’s what drivers who use those interstates can expect:
When traffic is flowing freely, the messages will tell drivers which lane is closed and how many miles ahead they must merge. The idea is that in light traffic, everyone can start moving into the correct lane well ahead of the work zone.
When average speeds approaching the work zone fall below 40 mph, the message boards will tell drivers to be alert for either slow or stopped traffic and how far ahead those conditions exist.
When traffic is heavier and has slowed below 25 mph – or even stopped – for at least 1.5 miles long, signs will tell drivers where the backups are occurring to “Use Both Lanes To Merge Point.” In these situations, NCDOT does not want motorists to merge until they reach the work zone, where they can take turns filing into a single lane.
The Dynamic Zipper Merge system does not work for every work zone. Because of the complexity of setting up the sensors, the system functions best for highways with travel lane reductions that will last for several months.
Engineers at the department have spent the past several weeks fine-tuning the system where it has been deployed, and they will evaluate where else it could be deployed in the future.
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