The Institute for Transportation Research and Education at North Carolina State University conducted a study for the North Carolina Department of Transportation (NCDOT) observing various treatments on roadways for affecting merging behavior in order to improve travel times. These included zipper merge signage wide dotted white lane lines, and elongated route shields for pavement markings. The zipper merge was implemented at three sites across central and eastern North Carolina, with one being a rural arterial permanent two-to-one lane drop, another being a suburban freeway permanent three-to-two lane drop, and the last being a rural freeway two-to-one temporary lane drop inside of a work zone. Lane utilization was not proven to be greatly affected by this treatment, with the greatest increase in ending lane traffic at any site being five percent, although this is likely due to sign misunderstanding. Travel times at these sites generally decreased modestly, with some increases as well. The increases may be due to outside factors like crashes, but the actual cause is unknown. The most significant increase was at the work zone site, which utilized a dynamic zipper merge setup and saw a decrease in travel time of one minute, which equates to an 11 mile per hour increase in space mean speed. The biggest improvement observed with the implementation of the zipper merge was the safety improvement, as far fewer vehicles entered the shoulder in order to merge after implementation of the zipper merge. As for the wide dotted line sites, particularly at the freeway site studied, entering vehicles merged sooner and exiting vehicles merged later, which was determined to be a positive finding as it meant fewer interactions between vehicles while they were attempting to leave or enter the auxiliary lane between ramps. Lastly, the elongated route shield sites studied did not appear to see a significant change in crashes after having these pavement markings installed.
