Optimizing Work Zone Zipper Merge Using Federated Driving Simulators

Sun, Carlos; Edara, Praveen; Anowar, Sabreena; Canfield, Casey · 2021 · ROSA P / Missouri. Department of Transportation. Construction and Materials Division

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Summary

This study addresses the inefficiencies and safety risks associated with traditional early-merge strategies at work zone lane closures, such as wasted lane capacity, extended queues, and aggressive queue-jumping behavior. To mitigate these issues, the researchers investigated the optimization of the "zipper merge" (late merge) strategy, which encourages drivers to use both lanes until the taper point. The research focused on four key deployment factors: the necessity of public education, the impact of traffic speed, the effect of traffic flow volume, and the optimal placement of Changeable Message Signs (CMS). The methodology combined a literature review, an analysis of existing educational materials, and a controlled driving simulator experiment involving 50 licensed Missouri drivers. The simulator study allowed for the isolation of specific variables under congested conditions that are difficult to replicate in field studies. Participants underwent pre- and post-education phases, where they received concise instructional materials about zipper merge protocols. The experiment tested driver behavior across varying traffic speeds (40 mph and 55 mph), traffic flows (medium and high volumes), and CMS placements (300 feet vs. 700 feet from the taper). The results demonstrated that public education is critical for compliance, as over 60% of participants were initially unfamiliar with zipper merge and many misinterpreted standard signage. Education significantly altered driver behavior; after instruction, drivers signaled to merge 570 feet closer to the work zone and executed the merge 747 feet closer to the taper compared to pre-education baselines. Regarding operational conditions, while drivers preferred lower speeds and higher traffic volumes, simulator data showed that zipper merge remained effective at higher speeds (55 mph) and moderate traffic flows (approximately 700 vehicles per hour per lane). Furthermore, placing the CMS closer to the taper (300 feet) resulted in statistically significant improvements in merge timing, encouraging drivers to utilize the closed lane capacity more effectively. The study concludes that successful zipper merge implementation requires robust public education to overcome ingrained early-merge habits and signage confusion. The authors recommend that the Missouri Department of Transportation adopt specific engineering policies, including placing CMS signs near the taper and utilizing concise, "chunked" educational materials in both written and video formats. These findings provide a data-driven framework for improving work zone efficiency, reducing congestion, and enhancing driver safety through optimized late-merge strategies.

Key finding

Drivers signaled and merged significantly closer to the taper after receiving education, and zipper merge operations remained effective under higher speeds and moderate traffic flows despite driver preferences for lower conditions.

Methodology

simulator

Sample size: 50

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

Topics

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• work zones
• perceptual countermeasures
• traffic density

Information type

What kind of knowledge this paper contributes, grouped by family — independent of topic (what it is about) and method (how it was studied).

• Applied Guidance: countermeasure evaluation
• Empirical Findings: observational prevalence
• Methodological Resource: tool software