The techniques used in this study permit the determination of sign visibility under controlled conditions for observers with both normal and reduced visual acuity. Sixteen familiar road sign messages (regulatory and warning) were examined in both alphabetic and symbolic form for observers with visual acuities from normal to as low as 6/21. Threshold legibility distances were calculated using probit analysis for individual signs and groups of signs. The experiments show that: (a) the average 50 percent threshold legibility distance for symbolic signs is about twice that for alphabetic signs for all levels of visual acuity; (b) the shape coding included on the signs does not enhance their legibility among a set of signs; (c) the sign size required for 0.95 probability of correct identification is approximately 1.7 times larger than the size giving 0.50 probability of correct identification; and (d) reduced visual acuity has a predictable effect on legibility distance, e.g. a change in visual acuity from 6/6 to 6/12 halves the 50 percent threshold legibility distance. Practical sign design for the actual driver population is discussed and, it is concluded that the use of symbolic sign messages and larger alphabetic sign messages is required.

  • Record URL:
  • Availability:
  • Corporate Authors:

    ARRB Group Ltd.

    Vermont South, Victoria  Australia 
  • Authors:
    • Jacobs, R J
    • Johnston, A W
    • Cole, B L
  • Publication Date: 1975-5

Media Info

  • Pagination: p. 68-86
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00133530
  • Record Type: Publication
  • Source Agency: Highway Safety Research Institute
  • Files: TRIS, ATRI
  • Created Date: Aug 23 1976 12:00AM