Nighttime Legibility of Ground-Mounted Traffic Signs as a Function of Font, Color, and Retroreflective Sheeting Type

Chrysler, Susan T.; Carlson, Paul J.; Hawkins, H. Gene · 2002 · ROSA P / Texas Transportation Institute. Texas A&M University

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Summary

This study investigates the nighttime legibility of ground-mounted traffic signs, specifically examining how font type, sign color, and retroreflective sheeting material affect visibility. The research was motivated by the aging driver population and the need to optimize sign design for safety, as standard Highway Series fonts have remained unchanged for decades despite advancements in retroreflective materials. The study aimed to determine if experimental fonts or specific sheeting types could improve legibility distances for older drivers under nighttime conditions. The researchers conducted a closed-course nighttime field study involving 24 participants aged 55 to 75. Participants drove a passenger sedan at 30 mph along a designated course, attempting to read ground-mounted signs positioned on the right shoulder. The experimental design utilized 48 signs, each measuring 12 inches by 30 inches with 6-inch letters. Three font types were tested: the standard Highway Series D, Clearview Condensed Road (used for white-on-green signs), and a D-Modified font with thicker strokes (used for black letters on white, yellow, and orange backgrounds). Additionally, three types of retroreflective sheeting were evaluated: ASTM Types III, VIII, and IX. The primary metric was the legibility distance, defined as the distance at which drivers could successfully read the sign text. The results indicated no significant difference in legibility performance between drivers aged 55–64 and those aged 65–75. Overall legibility distances ranged from 143 to 206 feet, yielding legibility indexes between 24 and 34 feet per inch of letter height. Sign color was a significant factor, with yellow and white signs producing the longest legibility distances, followed by green, and then orange. Retroreflective sheeting type also significantly impacted legibility, though the specific effects varied depending on the sign color. Contrary to expectations, the font results showed that the standard Highway Series D performed better than or equivalent to both experimental alternatives. Notably, the tested version of Clearview performed slightly worse than the standard font. The findings suggest that for small, ground-mounted signs, the standard Highway Series D font remains effective and may outperform newer experimental fonts like Clearview in certain contexts. The study highlights that color and retroreflective sheeting are critical variables in sign design, with yellow and white offering superior nighttime visibility. These results provide practical guidance for traffic engineers, indicating that optimizing sheeting type and color selection may yield greater improvements in nighttime legibility for older drivers than altering font styles. The research supports the continued use of standard fonts while emphasizing the importance of material and color choices in enhancing sign conspicuity and readability.

Key finding

Yellow and white sign backgrounds yielded the longest legibility distances, and the standard Highway Series D font outperformed or matched experimental fonts including Clearview Condensed.

Methodology

on_road

Sample size: 24

Provenance

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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.

• sign visibility legibility
• vehicle conspicuity
• signage environment
• visibility analysis litigation
• roadway lighting effects