PROGRESS REPORT ON PLANTING FOR SCREENING HEADLIGHT GLARE AND FOR TRAFFIC GUIDANCE

WHEN THE GEOMETRIC DESIGN STANDARDS FOR THE MEDIAN WHEN THE GEOMETRIC DESIGN STANDARDS FOR THE MEDIAN ARE REDUCED BELOW 50 FEET IN WIDTH, THE NEED FOR PLANTING FOR SCREENING HEADLIGHT GLARE BECOMES VERY APPARENT. THIS NEED FOR SCREEN PLANTING IS GREATLY INCREASED WHEN UPPERBEAM HEADLAMPS ARE IN USE. AT SHORT DISTANCES OF ABOUT 200 FEET THE LUMINANCE VALUES FOR THE UPPER BEAMS ARE ABOUT TEN TIMES THOSE FOR LOWER BEAMS. AT DISTANCES GREATER THAN 200 FEET THE UPPER BEAMS GIVE FIFTEEN TO TWENTY-FIVE TIMES THE LUMINANCE FOR LOWER BEAMS. FROM THESE DATA, ONE CAN READILY SEE WHY IT IS IMPORTANT TO BE ABLE TO HAVE THE UPPER BEAM HEADLAMPS CONTINUOUSLY IN OPERATION WHEN DRIVING AT MAXIMUM SPEED. WHERE THE MEDIAN IS 50 FEET OR MORE, THE PLANTING COST FOR SCREENING HEADLIGHT GLARE MAY BE KEPT TO THE MINIMUM. PLANTING TO CONTROL THE HEADLIGHT- GLARE PROBLEM WILL OCCUR ONLY WHERE THE HORIZONTAL CURVATURE OF THE ALIGNMENT ALLOWS THE LIGHTS OF THE OPPOSING MOTOR VEHICLE TO SHINE ACROSS THE MEDIAN INTO THE EYES OF THE DRIVER TRAVELING IN THE OPPOSITE DIRECTION. VERTICAL CURVATURE OF ROADWAYS WILL PERMIT ONCOMING HEADLIGHTS TO PENETRATE OVER THE TOPS OF THE PLANTING UNLESS THE SIGHT LINES ON THE HIGHWAY PROFILES ARE PLOTTED IN ORDER TO DETERMINE THE EXACT HEIGHT OF PLANT MATERIAL REQUIRED. WHEN THE DESIGN STANDARDS ALLOW A NARROWER MEDIAN, THE PROBLEM OF ELIMINATING HEADLIGHT GLARE BY SCREEN PLANTING BECOMES MORE ACUTE. A SURVEY OF EXPERIMENTATION IN A DOZEN STATES SUGGESTS THAT MEDIAN PLANTINGS, TO BE EFFECTIVE, MUST ULTIMATELY MEASURE 4 1/2 TO 5 FEET IN HEIGHT AND THE COMPOSED OF PLANT MATERIAL THAT WILL PROVIDE A DENSE TWIG GROWTH. COMBINATION PLANTINGS OF CONIFEROUS TREES, BROAD-LEAF EVERGREENS, AND DECIDUOUS SHRUBS ARE MOST EFFECTIVE FOR YEAR-ROUND USE. /AUTHOR/

  • Supplemental Notes:
    • No 496, pp 55-73, 7 FIG, 2 TAB, 12 PHOT, 5 REF
  • Authors:
    • Deakin, O A
  • Publication Date: 1957

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  • Accession Number: 00205104
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Nov 22 1971 12:00AM