Zipper Merge Gains Traction

October 17, 2016

An Arizona Department of Transportation project in the West Valley this weekend will employ whatís known as a zipper merge to get traffic into one lane in a way that reduces delays.

The merge will be used during daytime hours on westbound Interstate 10 between Watson Road and State Route 85 in Buckeye, where one of the two lanes will be closed from 10 p.m. Friday, Oct. 7, until 5 a.m. Monday, Oct. 10. The zipper merge will be in place between 6 a.m. and 8 p.m., when traffic is heavier. At night, drivers should merge earlier when it is convenient and safe.

This work also will close on- and off-ramps at Miller Road from 9 p.m. Friday, Oct. 7, until 9 p.m. Saturday, Oct. 8, and westbound I-10 connecting ramps to SR 85 from 9 p.m. Saturday, Oct. 8, until 5 a.m. Monday, Oct. 10.

The zipper merge works best for construction projects with heavier traffic and slower speeds. Digital message boards instruct drivers to remain in both lanes until right before the lane restriction. Then vehicles take turns getting into the open lane, much like a zipper closes.

For the zipper merge to be as effective as possible, drivers approaching the work zone need to cooperate and let go of the notion that they need to merge early. In the interest of safety and efficiency, drivers also must resist the urge to straddle both lanes to keep others from getting around them.

The payoff: A zipper merge can reduce the length of a traffic backup by up to 40 percent, according to the Federal Highway Administration, while providing more predictable driver behavior. Keeping traffic in both lanes longer enhances safety by reducing the speed differential between the lanes.

This will be ADOTís second use of the zipper merge, which was also employed earlier this year at an I-10 bridge project east of Tucson (shown in the video above). ADOT will evaluate the results to see if it should be used for future projects.

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