When a lane on a highway is temporary closed due to construction and traffic is backed up, drivers may see road signs asking them to merge in a specific fashion known as the zipper merge (or late merge). In certain situations, this makes the traffic flow more efficiently for drivers in both lanes. A zipper merge has drivers use both lanes until reaching a defined merge point. Drivers then take turns merging into the open lane in a zipper like fashion.

Remember, drivers who are changing lanes must signal, while drivers who are remaining in the through lane must let in one vehicle.