THE EFFECT OF WIDE-ANGLE HEADLIGHT ILLUMINATION ON DRIVER PERFORMANCE

The purpose of this study was to identify possible improvements in the present U.S. low beam head-light system, using an instrumented passenger car to evaluate the effect of experimental wide-angle low beam lighting on various driver performance measures: speed, brake pressure, longitudinal acceleration, steering wheel position, lateral acceleration, lateral lane position, and electrodermal response (GSR), for over 1,000 vehicle miles (30 hours) on a winding rural highway at night. The present U.S. low beam system poses a visibility problem in rural night driving for two reasons: down-the-road preview distance in curves is severely limited due to the narrow angular coverage of U.S. low beams; and many drivers tend to use low beams continuously on two-lane rural roads, even after opposing traffic has passed. Improvements in the U.S. low beam system may contribute significantly to a reduction in the much higher nighttime increase in the rate of single vehicle fatal accidents which occur on curves vs. straight sections. Eighteen subjects in Experiment 1 and ten subjects in Experiment 2 provided performance data for 134 test runs, sampled by a digital computer-compatible tape recorder at 5 Hz. This time-based data was subsequently computer processed and converted to distance-based data in order to average across subjects for each 10 m segment of the test road, and to permit an analysis of variance within subjects for lighting pattern, left/right curve vs. straight, outbound vs. inbound, first four runs vs. second four runs. Average values of the driver performance measures showed only slight differences as a function of the different headlight patterns, but the statistical significance of these differences suggests that another approach to analysis of the data base would show much stronger lighting effects. Complex interactions of the lighting variable with roadway geometry and familiarity showed that lighting affects driver performance only at specific critical points along the roadway. High beam produced significantly lower electrodermal response than the three low beam systems, and the widest low beam system showed greater lateral lane position variability than high beam and the other two low beam systems. In a survey after the test runs, subjects consistently preferred the widest-angle low beam system for driving on the winding rural highway, even over the standard high beam system. (NHTSA)