LEGIBILITY DISTANCES OF HIGHWAY DESTINATION SIGNS IN RELATION TO LETTER HEIGHT, LETTER WIDTH, AND REFLECTORIZATION

A PREVIOUS PAPER BY ONE OF THE AUTHORS ANALYZED SIGN EFFICIENTY INTO (1) PURE LEGIBILITY (LONG TIME), (2) GLANCE LEGIBILITY (SHORT GLANCE), (3) TARGET VALUE AND (4) PRIORITY VALUE, THE LATTER TWO FACTORS DEALING WITH ATTENTION GETTING CHARACTERISTICS. AN EXTENSIVE STUDY IS REPORTED OF THE PURE LEGIBILITY OF STANDARD SERIES B (NARROW LETTERS) AND SERIES D (WIDE LETTERS), BLACK ON WHITE DESTINATION SIGNS. LETTER HEIGHTS FROM 6 TO 24 INCHES WERE USED. A TOTAL OF ABOUT 400 PEOPLE ACTED AS OBSERVERS AND MADE ABOUT 4600 INDIVIDUAL OBSERVATIONS. CHARTS SHOW MAXIMUM LEGIBILITY DISTANCE IN RELATION TO HEIGHT AND WIDTH OF LETTER, REFLECTORIZATION AND ILLUMINATION (DAY VS. NIGHT). THE DETERMINATION FOR EACH SIZE, WIDTH AND TYPE OF LETTER DEPENDED ON A GROUP OF FROM 50 TO 276 OBSERVATIONS. THE WIDTH LETTERS SHOWED GREATER EFFECTIVENESS THAN THE NARROWER ONES, BUT BOTH WIDTHS LOST APPROXIMATELY 15 PER CENT OF THEIR LEGIBILITY DISTANCE UNDER NIGHT CONDITIONS (FLOODLIGHTED). ROUGH PRACTICAL NORMS FOR DAY CONDITIONS AND "NORMAL" VISION GAVE 50 FT. PER IN. OF LETTER HEIGHT FOR THE WIDE AND 33 FT. PER IN. FOR THE NARROW LETTERS. IT IS SUGGESTED THAT THESE VALUES SHOULD BE REDUCED IN PRACTICE TO TAKE ACCOUNT OF THE POOR VISION OF MANY DRIVERS KNOWN TO BE ON THE HIGHWAYS. THE RESULTS ALSO INDICATED THE ADVANTAGE OF FLOODLIGHTED SIGNS AT ANY LOCATION WHERE A LIGHTED BACKGROUND IS ENCOUNTERED. REFLECTORS REDUCED THE DAYTIME LEGIBILITY OF THE LETTERS ONLY IN THE LARGEST SIZES, AND THE REFLECTORIZED LETTERS WERE AS EFFECTIVE AS THE FLOODLIGHTED ONES AT NIGHT AGAINST A DARK BACKGROUND. IT IS SUGGESTED THAT GLANCE LEGIBILITY TESTS WILL PROBABLY REDUCE THE LEGIBILITY DISTANCES SOMEWHAT, AND THAT A CORRECTION FACTOR MAY BE DEVELOPED, TO CORRESPOND MORE CLOSELY TO BRIEF GLIMPSES OF SIGNS OFTEN NECESSITATED BY HEAVY TRAFFIC. IF THE RESULTS ARE APPLIED TO GIVE THE MOTORISTS 10 SECONDS WARNING AT A SPEED OF 50 MILES PER HOUR, AT LEAST A 10 INCH SERIES D OR A 12 INCH SERIES B LETTER IS NEEDED FOR NIGHT CONDITIONS. /AUTHOR/

  • Supplemental Notes:
    • Vol 19, pp 321-335, 14 FIG, 2 TAB
  • Authors:
    • Forbes, T W
    • Holmes, R S
  • Publication Date: 1940

Media Info

  • Monograph Title: Proceedings of the Nineteenth Annual Meeting of the Highway Research Board Held at Washington, D.C. December 5-8, 1939
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00225968
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: Oct 3 1971 12:00AM