Work vehicle warning lights : color options and effectiveness.

Howell, Brian; Pigman, Jerry; Agent, Ken · 2015 · ROSA P / University of Kentucky Transportation Center

archive: archived pipeline: cataloged verified

Get this paper ↗ (full text — opens at the source; we link to it, we don't host it)

Summary

This study addresses the lack of national standards for warning lights on highway work vehicles and the specific need for the Kentucky Transportation Cabinet (KYTC) to establish effective lighting protocols. The research was motivated by stakeholder concerns that red warning lights on KYTC vehicles could be confused with emergency service vehicles, leading to a prohibition on red lights. The primary objective was to synthesize existing literature, statutes, and state practices to recommend optimal color options, light sources, and configurations for enhancing worker safety and motorist visibility. The researchers conducted a comprehensive review of regulations, including Kentucky Revised Statutes and the Manual on Uniform Traffic Control Devices (MUTCD), alongside guidance from the American Association of State and Highway Transportation Officials (AASHTO). They analyzed prior state-level studies from Illinois, Indiana, Iowa, Minnesota, Ohio, and Texas regarding light color effectiveness. Additionally, the team executed two external surveys: one of LED vendors to assess available product colors and a second of state Department of Transportation (DOT) agencies to determine current practices regarding light color, source, intensity, and placement. The DOT survey received 16 responses detailing agency policies and previous research findings. The literature review revealed that amber and white lights elicited better motorist responses than blue or red, with amber being strongly associated with maintenance operations. AASHTO guidelines recommended asynchronous flashing patterns with slow frequencies (1 Hz) and LED sources for optimal reaction times. State studies generally supported amber as the primary color, though Ohio recently adopted green strobes to reduce rear-end crashes. The vendor survey confirmed that fluorescent yellow-green LEDs were unavailable, while amber, blue, green, red, and white were common. The DOT survey indicated that 100% of responding agencies used amber lights and LEDs, with over 75% placing lights on vehicle roofs for 360-degree visibility. Practices varied significantly regarding the differentiation of light colors by vehicle type and intensity adjustments for day versus night conditions. Based on these findings, the authors recommend that KYTC adopt amber and white as the primary warning light colors for work vehicles. They advise using LED bulbs with an asynchronous flashing pattern at slow frequencies to maximize motorist response without causing excessive glare. Furthermore, the report recommends placing warning lights at high elevations on the vehicle against a solid-colored background to ensure contrast and visibility. The study concludes that while amber is the standard, further investigation is needed to determine the feasibility of yellow-green LEDs as a viable warning light option.

Key finding

All 16 responding state DOTs reported using amber lights as part of their warning light ensemble with LED sources, and national research indicates amber and white lights elicit better motorist responses than red or blue.

Methodology

survey

Sample size: 16

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 (9 acquisition events logged).

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

Topics

Ranked by relevance to this paper. Hover a topic for its definition.

• emergency work zone conspicuity
• vehicle conspicuity
• roadway lighting effects