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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations

This report is an archived publication and may contain dated technical, contact, and link information
Publication Number: FHWA-RD-94-069
Date: July 1997

Symbol Signing Design for Older Drivers



There has been an increasing use of symbols, including those on highway signs, over the past 2 decades. At the same time, there has been a rapid growth in both the numbers and proportions of older drivers. Research on symbols has shown that many symbols are poorly understood and/or difficult to recognize at a distance, especially by older drivers. In spite of the considerable research on traffic sign symbols, there has not yet been a thorough evaluation of all symbols used on U.S. highways.

This report presents a review of the literature on information processing abilities of older drivers and human factors research on traffic sign symbols. It describes a series of studies, surveys, and laboratory experiments that examined symbols in the U.S. Manual on Uniform Traffic Control Devices (MUTCD). Initially all symbols in the Manual were evaluated for comprehension and daytime legibility distance among drivers of all ages. This was followed by evalation of a set of 18 symbols using measures of nighttime legibility (with and without glare), reaction time, glance legibility, and conspicuity. Older drivers were found to have poorer understanding of the symbols, as well as shorter legibility distances, higher glance legibility thresholds, reaction times, and conspicuity search times. Glare was found to reduce legibility of signs only for older drivers. Modifications and redesigns to 13 of the symbols resulted in better understanding of 3 symbols and increased legibility of 11 new designs. Understanding and legibility of five novel symbols which were developed for this project were found to be comparable to those of the redesigned symbols.

Recommendations were made for changes to specific symbols and guidelines were proposed for the design of symbol traffic signs. A proposal was made for the use of design optimization techniques, using computer, in the development and evaluation of signs.


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1. Report No.


2. Government Accession No. 3. Recipient's Catalog No.
4. Title and Subtitle


5. Report Date

July 1997

  6. Performing Organization Code
7. Author(s)

Robert Dewar, Donald Kline, Frank Scheiber, and Allen Swanson

8. Performing Organization Report No.
9. Performing Organization Name and Address

Swanson Transportation Consultants, Ltd.
P.O. Box 83001, Canyon Meadows Post Office
Calgary, AB Canada, T2W 6G8

10. Work Unit No. (TRAIS)


  11. Contract or Grant No.


12. Sponsoring Agency Name and Address

Office of Safety and Traffic Operations R&D
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101–2296

13. Type of Report and Period Covered

Final technical report June, 1991 June, 1994

  14. Sponsoring Agency Code
15. Supplementary Notes

Contracting Officer's Technical Representative (COTR) : Dr. Truman Mast HSR–30

16. Abstract

This project evaluated the effectiveness of symbol traffic signs for young, middle–aged and elderly drivers. Daytime legibility distance and comprehension of 85 symbols in the Manual on Uniform Traffic Control Devices (MUTCD) were measured. Legibility distance under night and night–with –glare conditions, glance legibility, reaction time and conspicuity were measured for 18 of these symbols. Selected symbols were modified or redesigned and five novel symbols were designed, using an image–processing iterative filterredesign approach. These new signs were evaluated on measures of comprehension and legibility distance under day, night and night–with–glare conditions. Of the 85 symbols many were well understood, but 10 were understood by fewer than 40% of drivers. Increased driver age was associated with lower comprehension levels and legibility distances (under all test conditions), as well as higher glance legibility thresholds, reaction times and conspicuity search times. Modifications and redesigns to the symbols resulted in better understanding of three messages and improved daytime legibility distances of 11 of the new signs. Glare reduced legibility of the signs only for the elderly drivers. Recommendations were made for changes to specific symbol signs. Guidelines were proposed for the design of symbol traffic signs, and a proposal was made for design optimization techniques to be employed in the future development and evaluation of such signs.

17. Key Words

symbols, traffic signs, comprehension, Legibility distance, glance legibility, reaction time, conspicuity, older drivers, night legibility, glare

18. Distribution Statement

No restrictions. This document is available to the public through the National Technical Information Service, Springfield, Virginia, 22161.

19. Security Classif. (of this report)


20. Security Classif. (of this page)


21. No. of Pages


22. Price

Form DOT F 1700.7 (8–72) Reproduction of completed page authorized



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