Driving safety tips and resources from the Arizona Department of Transportation at FocusOnDriving.com keep motorists prepared on Arizona’s roads.

Zipper merge: In the right situations, two lanes can be better than one

By Tom Herrmann / ADOT Communications

The concept is simple: Using two lanes as long as possible into a lane restriction can move traffic more efficiently than everyone trying to merge earlier. For a construction project with the right combination of traffic volume and anticipated slowdown, a line of vehicles that could stretch for a mile or more in one lane can have a shorter backup and move more efficiently in two – as long as drivers cooperate at the merge point.


ADOT has used the zipper merge for a few projects now, including construction of a new westbound Davidson Canyon bridge on I-10 east of Tucson. Now drivers along I-10 in western Arizona will use it next week.

From 6 a.m. to 6 p.m. on Tuesday, April 25, the zipper merge will be in place on eastbound I-10 about 20 miles east of Quartzsite. A lane will be closed between mileposts 37 and 39 for a paving project.

With old-fashioned merges, most drivers move over to the appropriate lane as soon as they see traffic signs.

With the zipper merge, traffic engineers want drivers to remain in their lanes and merge just before the lane closure begins. Signs saying “merge here” and “take turns merging” show when it’s time to merge.

The zipper merge works best for construction projects with heavier traffic and slower speeds.

Kansas, Colorado, Nevada, Georgia, Missouri, Minnesota and Washington are among other states using the zipper merge.

ADOT is continuing to evaluate the results from use of the zipper merge to see if it should be used for future projects.