Evaluation of Early Merge Static Work Zone Signing in Oklahoma

This research examined the safety and operational benefits of having traffic merge early into the open lane prior to a work zone merge area. A 2007 law in Oklahoma adopted the use of additional “STATE LAW MERGE NOW” static signing in the advance warning areas approximately 1/2-mile upstream from freeway merge areas. Work zones that were continuations from the 2006 construction season did not use this signing, while new work zones did. This provided a unique opportunity to compare the impact of early merge signing in actual work zone environments. Measures of effectiveness examined included the number and percentage of traffic that remained in the closed lane and the number of conflicts that occurred at the merge area. It was found that the early merge signs did not appear to reduce the percentage of vehicles that remained in the closed lane. However, at least for right-lane closures, there appeared to be a significant benefit to using the STATE LAW MERGE NOW signing to reduce the number of observed conflicts at the merge area. This was evident when the hourly volumes were more than 550 vph. It seemed likely that although the early merge signs themselves did not improve early merging, the signs seemed to encourage drivers to consider earlier how they would make their merge maneuver, so when the reached the merge area the drivers that must merge were more likely to be able to make the merge without the need to vie for position against other drivers.