Citation

Mortimer RG, Becker JM. Transp. Res. Rec. 1974; 502: 34-40.

Copyright

(Copyright © 1974, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

unavailable

PMID

unavailable

Abstract

A digital computer simulation was used to evaluate some factors that determine the overall effectiveness of current and proposed beams. Specifically, simulation was used to derive predicted visibility distances for a typical U.S. low beam and a proposed midbeam, with correct aim and with 1-deg (0.017-rad) upward or downward misaim. This demonstrated that aiming errors of this amount significantly affect a driver's visibility and the glare intensities to which opposing drivers are exposed. The midbeam offered a 20 percent increase in visibility of a target located at the right edge of the lane on a 2-lane road compared to the present low beam when the beams were correctly aligned. Because the midbeam provides greater visibility than the low beam, it was shown that it is appropriate to dim earlier from high beam to midbeam than to low beam, thereby obtaining better visibility and earlier reduction of high-beam glare. Use of the midbeam as the major meeting beam would make it more feasible to increase the intensity of the high beam. An examination of glare intensities from the beams in rearview mirrors showed the importance of lamp aim and mirror reflectivity to glare discomfort. For the conditions studied, it was concluded that the midbeam offers a satisfactory increase in visibility compared to the low beam and does not significantly increase glare if lamp aim is adequately controlled.