The technical literature was reviewed with respect to the loss of visibility distance caused by automobile windshields or other optical filters. A series of nighttime luminance measurements in the field provided baseline data for a visibility distance computer model that was developed to investigate nighttime visibility of diffusely reflective targets under low-beam illumination conditions seen through automobile windshields having different transmittances. The computer model offers three alternative luminance contrast threshold models: (a) Adrian's target visibility algorithm, (b) PCDETECT, and (c) Blackwell's 1946 contrast threshold data. The new model, which is based on Blackwell's 1946 data, considers the effects of age and observation time and determines the actual contrast from the target luminance, which depends on the target reflectance, the selected headlamps, and the current observation distance. Percent visibility distance loss graphs, as a function of the initial visibility distance (D sub 0) (using no windshield) were established. A tentative field factor of 2.28 for the Blackwell data was determined. The obtained percent visibility distance loss data were compared with those published earlier by Haber in 1955. This comparison indicates that the percent distance loss functions shown by Haber are misleading and wrong because they are proposed to apply for a target with a constant mean linear dimension of 91.4 cm (3 ft) over the entire initial visibility distance range. Furthermore, the data presented by Haber are conservative and too high. On the basis of the results of this investigation, it would appear to be of benefit to further validate the results in the field and to review the appropriateness of established minimum luminous transmittance standards.


  • English

Media Info

  • Features: Figures; References; Tables;
  • Pagination: p. 128-139
  • Monograph Title: Traffic control devices, visibility, and railroad grade crossings
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00714888
  • Record Type: Publication
  • ISBN: 0309061601
  • Files: TRIS, TRB
  • Created Date: Dec 12 1995 12:00AM