A Single Portable Dynamic Message Sign Located Upstream from a Freeway Lane Closure Can Increase Merge Lane Utilization by Up to 3.2 Percent Compared to Static Signage.
Field Evaluation of Three Work Zones Lane Closures in 2023 and 2024 in Michigan Assessed Lane Utilization Behavior Under Zipper Merge Lane Control.
Michigan, United States
Improving the Effectiveness of Zipper Merge Lane Control in Freeway Work Zones
Summary Information
The late merge, or “zipper” merge, is a commonly used strategy to increase work zone capacity by encouraging drivers to stay in their lanes until they reach a defined merge area, where they take turns merging. This study considered zipper merge conditions in tandem with portable dynamic message signs (i.e., portable changeable message signs (PCMS)). Field evaluations were conducted at three freeway work zone lane closures in in Michigan in 2023 and 2024 to assess lane utilization behavior under zipper merge lane control. This study also explored strategies to improve compliance in advance of single-lane closures.
METHODOLOGY
The field evaluations focused on utilization of the soon-to-be-closed lane, measured as the proportion of all vehicles that were in that specific lane. Three freeway work zones along I-94, I-96, and M-53 were evaluated. The following sign test conditions were tested using PCMS.
- Condition A: Static zipper merge signage.
- Condition B: Static zipper merge signage plus one PCMS sign upstream of the taper displaying “USE BOTH LANES” and “DURING BACKUPS” on alternating panels.
- Condition C (Tested at I-94 and I-96 only): Conditions A and B plus a second PCMS sign downstream closer to the taper, alternating between the messages “MERGE HERE” and “TAKE TURNS.” on alternating panels.
FINDINGS
For Condition B:
The field evaluations focused Three freeway work zones along I-94, I-96, and M-53 were evaluated. The following sign test conditions were tested using PCMS:
- Condition A: Static zipper merge signage.
- Condition B: Static zipper merge signage plus one PCMS sign upstream of the taper displaying “USE BOTH LANES” and “DURING BACKUPS” on alternating panels.
- Condition C (Tested at I-94 and I-96 only): Conditions A and B plus a second PCMS sign downstream closer to the taper, alternating between the messages “MERGE HERE” and “TAKE TURNS.”
For Condition C:
- On I-96, lane utilization increased by 3.2 and 1.9 percent at 1,800 ft and 2,500 ft upstream of the taper, respectively.
- When the data were combined for both sites, compared to Condition B, installing a second PCMS increased lane utilization by only 0.5 and 0.2 percent within half a mile, and beyond one mile from the start of the taper, respectively.
Volume-Dependent Results:
- The results showed that for every 100 vehicles/hour increase in traffic volume, lane utilization increased by 0.25 to 0.83 percent across sites.
- The average increase in lane utilization across all sites was 0.62 percent for every 100 vehicles/hour.
