Summary Report: Improvements In Symbol Sign Design To Aid Older Drivers

Dewar, Robert; Swanson, Allen · 1994 · ROSA P / United States. Joint Program Office for Intelligent Transportation Systems

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Summary

This report addresses the critical need to evaluate and improve the effectiveness of symbol traffic signs for older drivers, a demographic group experiencing rapid growth and increased vulnerability to traffic accidents. Motivated by evidence that older drivers have higher accident rates—often due to failure to heed signs—and that many existing symbols are poorly understood or difficult to recognize at a distance, the study aimed to systematically assess symbol signs found in the U.S. Manual on Uniform Traffic Control Devices (MUTCD). The research sought to determine which symbols were problematic, develop improved designs, and establish guidelines for future sign development that account for age-related sensory and cognitive declines. The study employed a two-phase experimental design involving licensed drivers across three age groups: young (18–39), middle-aged (40–59), and older (60+). In Phase 1, researchers evaluated 85 standard MUTCD symbols for daytime legibility distance and comprehension. Based on these results, 18 symbols representing best, intermediate, and worst performance were selected for further testing. These 18 symbols were assessed under nighttime conditions, including scenarios with peripheral glare, as well as for glance legibility, reaction time, and conspicuity. In Phase 2, 13 of these symbols were modified or redesigned, and five novel symbols were created using an iterative image-processing approach. These new designs were then tested for comprehension and legibility under daytime, nighttime, and nighttime-with-glare conditions. The findings revealed that increased driver age was consistently associated with lower comprehension levels, shorter legibility distances, higher glance legibility thresholds, longer reaction times, and increased conspicuity search times. Specifically, glare was found to reduce sign legibility only for older drivers. Among the 85 standard symbols evaluated, 10 were understood by fewer than 40% of drivers. The modifications and redesigns proved effective: three redesigned symbols showed improved understanding, and 11 new designs demonstrated increased daytime legibility distances. Furthermore, the five novel symbols developed for the project achieved comprehension and legibility levels comparable to the redesigned symbols. The significance of this work lies in its comprehensive evaluation of symbol effectiveness across multiple metrics and its practical recommendations for traffic control authorities. The report proposes specific changes to existing regulatory, warning, guide, and recreational signs to enhance both comprehension and legibility. It also establishes design guidelines emphasizing consistency, simplicity, and uniformity to accommodate the visual and cognitive limitations of older drivers. Additionally, the study advocates for the use of computer-based design optimization techniques in future sign development, providing a framework for creating traffic signs that are safer and more accessible for an aging driving population.

Key finding

Older drivers exhibited significantly poorer symbol comprehension, shorter legibility distances, and slower reaction times than younger drivers, and peripheral glare reduced sign legibility only for the elderly.

Methodology

lab_experiment

Provenance

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Topics

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

• sign visibility legibility
• signage environment
• age related perceptual decline
• sensory abilities
• contrast sensitivity
• disability glare