The Joint Merge: Improving Work Zone Traffic Flows

NHTSA · 2013 · ROSA P / United States. Department of Transportation. Office of the Assistant Secretary for Research and Technology

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Summary

This study addresses the safety and efficiency challenges associated with work zone lane closures, which commonly cause congestion, delays, and increased crash risks. The research specifically evaluates the "Joint Lane Merge" (JLM) design against the conventional "Conventional Lane Merge" (CLM) specified in the Manual on Uniform Traffic Control Devices. While CLM grants right-of-way priority to the open lane, JLM utilizes blinking arrow signs to guide drivers in both lanes to merge using an alternating "zipping" pattern, granting equal right-of-way. The primary objective was to determine how these traffic control configurations influence driver behavior, workload, and safety. The researchers employed a full-scale passenger car simulator equipped with four screens to replicate interstate highway work zone scenarios. Thirty university students with valid driver licenses participated in the study. The experimental design compared JLM and CLM across two traffic density levels (high and low) and three lengths of advanced warning areas. Data collection focused on objective performance metrics, including average speed, maximum braking force, average deceleration, and the distance from the transition zone where lane changes occurred. Additionally, subjective workload measurements were gathered by asking participants to rate mental, physical, and temporal demands, as well as frustration, effort, and performance satisfaction after each trial. The results demonstrated that JLM outperformed CLM in both objective driving metrics and subjective driver experience. Participants reported lower mental activity, less effort, and higher satisfaction with JLM, noting an absence of time pressure associated with merging. Quantitatively, JLM yielded lower average operating speeds, deceleration, and braking forces compared to CLM. The most significant differences occurred at low traffic volumes, where merging speeds in JLM were 6 percent higher than in CLM. Furthermore, average braking force and deceleration in JLM were 34 percent lower than in CLM. Regarding merge timing, drivers in the CLM configuration stayed in the closed lane longer, initiating merges on average 1,090 feet prior to the transition zone, whereas JLM drivers began merging 1,950 feet prior. The study concludes that the Joint Lane Merge design reduces driver workload and improves traffic flow efficiency compared to conventional methods. By regulating task demands and preventing driver overload, JLM enhances safety and satisfaction. The findings suggest that implementing JLM can reduce congestion, increase road capacity, and improve safety within work zones. These results provide evidence for transportation designers and planners to adopt JLM strategies to optimize traffic flow and mitigate the negative impacts of lane closures.

Key finding

Under the Joint Lane Merge, average braking force and deceleration were 34 percent lower than the conventional merge and drivers began merging on average 1,950 feet ahead of the transition zone versus 1,090 feet for the conventional design.

Methodology

simulator

Sample size: 30

Provenance

The full processing record for this entry. Every stage of this paper's journey through the pipeline is logged — what ran, with which tool and model, how many attempts it took, and when it last completed. Discovered via bulk_ingest_rosap on 2026-05-23 (8 acquisition events logged).

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

Topics

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• work zones
• perceptual countermeasures