Evaluation of Lane Reduction and Late Merge Signing

Katz, Bryan J; Kissner, Erin; Filler, Erin; Jackson, Steve; Vaughan, Christopher L.; Cunningham, Christopher M. · 2023 · ROSA P / United States. Federal Highway Administration. Office of Research, Development, and Technology

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Summary

This study evaluates the effectiveness of static late merge (zipper merge) signing on arterial roads, addressing a gap in research where prior studies focused primarily on freeways or managed work zones. The research was motivated by inconsistent signing practices across transportation agencies and a lack of data on how specific sign designs influence driver behavior at static lane reductions. The primary objective was to identify sign series that best convey the late merge concept—encouraging drivers to use all lanes until the merge point—and to assess their impact on right lane utilization (RLU). The methodology comprised two phases: a laboratory study and a field study. The laboratory study involved 100 participants who evaluated five sign series alternatives through video-based simulations. Participants completed comprehension tests, subjective rankings, and created ideal sign series to determine which designs most effectively communicated the need to merge, the timing of the merge, and the right-of-way rules. Based on these results, a single hybrid sign series was selected for field testing. The field study was conducted at 12 sites across Maryland, North Carolina, and New Hampshire. Researchers installed cameras to capture driver behavior during three observation periods: before sign installation, immediately after (transition), and at least six weeks after (after). The primary metric was RLU, defined as the proportion of vehicles occupying the lane that ends at the merge point. Laboratory results indicated that sign alternatives 3, 4, and 5 were superior in conveying the zipper merge concept, particularly regarding the instruction to alternate merging. Consequently, a sign series combining elements from alternatives 4 and 5 was deployed in the field. Field results showed that installing the late merge signs increased RLU in the long term (after period) by an average of 3.3 percentage points, though no significant change occurred during the short-term transition period. Statistical modeling revealed that RLU was significantly lower at sites with merge arrow pavement markings, suggesting these markings may contradict the late merge message by implying early merging is required. Conversely, the presence of driveways or businesses on the right side of the road was associated with an 8.7-percentage-point increase in RLU, likely due to vehicles entering the roadway near the merge point. The study concludes that the tested late merge sign series effectively increased right lane utilization at both the intersection and the merge point over time. The findings suggest that driver behavior changes gradually, likely as familiar drivers learn the new signage. The research highlights that pavement markings, particularly merge arrows, can undermine the effectiveness of late merge signs. The authors recommend supplementing the sign series with a "USE BOTH LANES" sign and implementing public outreach campaigns to further improve compliance and clarify that using all lanes until the merge point is the intended and beneficial behavior.

Key finding

Installing late merge signs increased right lane utilization at both the intersection and merge point in the long term, though effectiveness was significantly reduced at sites with merge arrow pavement markings.

Methodology

mixed_methods

Sample size: 100

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 (6 acquisition events logged).

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

Topics

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• signage environment
• perceptual countermeasures
• signaling behavior