An experiment was conducted which showed that distance estimates of a series of targets (at 5M to 25M distance) were greater and that size was over-estimated under fog conditions. Instances of apparent growth in size of objects with increased distance are discussed, particularly in relation to driving. The physics of visibility is discussed. It is pointed out that an object becomes invisible when its contrast with the background reduces to 2 per cent. An experiment confirmed that the contrast drops off exponentially with viewing distance in a given medium. The author discusses other distance clues and the adaptation of people moving to a climate of differing visibility. The influence of colour contrast on aerial perspective is considered in relation to the psychology of distance estimation. The part played by poor visibility by reducing visual clues is discussed, particularly by the impairment of stereoscopic acuity and the reduced visibility in the peripheral field of view. This is related to driving, particularly on motorways. The author concludes by stressing that the visual system (eyes and brain) becomes less efficient when the amount of visual information is low, and so fog not only reduces visual information but also leads to distortion. /TRRL/

  • Availability:
  • Corporate Authors:

    IPC Magazines

    66-69 Great Queens Street
    London WC2E 5DD,   England 
  • Authors:
    • Ross, H
  • Publication Date: 1975-6-19

Media Info

  • Features: Figures; Photos;
  • Pagination: p. 658-680
  • Serial:
    • Volume: 66
    • Issue Number: 954
    • ISSN: 0262-4079

Subject/Index Terms

Filing Info

  • Accession Number: 00129560
  • Record Type: Publication
  • Source Agency: Transport and Road Research Laboratory (TRRL)
  • Files: ITRD, TRIS
  • Created Date: Apr 7 1976 12:00AM