The Colorado Department of Transportation (CDOT) is updating its standards and installing new road signs to encourage the zipper-merge technique in work zones [1].

This shift in traffic management aims to reduce the significant delays often found in construction areas. By utilizing all available lanes until the merge point, the state expects to improve the overall efficiency of traffic flow during roadwork projects.

CDOT updated its standards on Sept. 22 [1]. The agency is implementing these changes across Colorado work zones, including high-traffic areas such as the Aspen Airport corridor [2, 4].

The zipper-merge requires drivers to continue driving in their lane until they reach the merge point, then take turns alternating into the open lane. This method prevents the premature merging that often creates long, single-file queues, a common source of frustration for motorists.

According to CDOT, the adoption of this technique can reduce work-zone traffic congestion by up to 40% [2, 3]. The agency said the goal is to maximize the use of pavement and decrease the length of traffic backups.

New signage will be placed in construction zones to notify drivers of the change and instruct them to take turns merging. The agency said the updated standards provide a formal framework for these installations across the state's highway system [1].

“CDOT standards were officially updated on September 22.”

The transition to a formal zipper-merge standard reflects a shift toward data-driven traffic engineering to handle construction bottlenecks. By legitimizing a practice that was previously viewed by some drivers as aggressive or incorrect, CDOT aims to standardize driver behavior to shorten queues and improve safety for both motorists and road crews.