HEADLAMP BEAM USAGE ON U.S. HIGHWAYS

HEADLAMP BEAM USAGE BY DRIVERS AT SEVENTEEN LOCATIONS IN THE CONTINENTAL UNITED STATES WAS ANALYZED IN A STUDY CONDUCTED FOR THE BUREAU OF PUBLIC ROADS. INFORMATION OBSERVED FOR EACH VEHICLE INCLUDED: TYPE OF VEHICLE, NUMBER OF HEADLAMPS, DIRECTION OF TRAVEL, SPEED, INITIAL BEAM USAGE, BEAM CHANGE IN RESPONSE TO OPPOSING VEHICLE, DISTANCE FROM OPPOSING VEHICLE WHEN BEAM CHANGE WAS ACCOMPLISHED, PRESENCE OF LEADING VEHICLE, AND TRAILING DISTANCES. OBSERVATIONS WERE MADE AT SELECTED TEST SITES IN FIFTEEN STATES AND INCLUDED: (1) FOURTEEN UNLIGHTED, RURAL, TWO-LANE SECTIONS (ONE REPEATED), (2) ONE UNLIGHTED, SUBURBAN, TWO- LANE SECTION, (3) ONE UNLIGHTED, SUBURBAN, FOUR-LANE SECTION WITH DEPRESSED MEDIAN, AND (4) ONE SUBURBAN, TWO-LANE SECTION WITH OVERHEAD LIGHTING. THE FOLLOWING CONCLUSIONS WERE DRAWN FROM THE FINDINGS OF THE INVESTIGATION: (1) HEADLAMP BEAM USAGE IS HIGHLY DEPENDENT ON TRAFFIC SITUATIONS, (2) MOST DRIVERS DIMMING THEIR HEADLAMPS FOR AN APPROACHING VEHICLE DID SO AT LONG INTERCAR DISTANCES, ASSUMING THAT THE OPPOSING DRIVER WOULD DO LIKEWISE, (3) OVER 60 PER CENT OF VEHICLES OBSERVED WERE TRAVELLING AT SPEEDS IN EXCESS OF THOSE CONSIDERED SAFE, (4) THERE ARE MARKED VARIATIONS IN BEAM USAGE HABITS OF DRIVERS FROM AREA TO AREA IN THE UNITED STATES, (5) USAGE OF HEADLAMP BEAMS WAS OBSERVED TO BE INDEPENDENT OF TOPOGRAPHY, (6) WEATHER CONDITIONS DO AFFECT HEADLAMP BEAM USAGE, ALTHOUGH TO A RATHER SMALL EXTENT IN SPECIFIC CASES OBSERVED, AND (7) MOST DRIVERS APPEAR TO BELIEVE THAT STREET LIGHTING GENERALLY PROVIDES VISIBILITY BETTER THAN THAT AVAILABLE FROM AUTOMOBILE HEADLAMPS.