G. Adachi

Michael J. Flannagan

M. Sivak

Brandon Schoettle

This study was designed to compare the illuminated surface areas of HID and tungstenhalogen low-beam headlamps in the U.S. A sample of 20 tungsten-halogen lamps and 17 HID lamps for model year 2000 vehicles in the U.S. was examined. The illuminated surface area was determined using a modified version of an ECE method for evaluating the illuminated surface of signaling devices. The main finding is that the HID low beams generally have smaller illuminated surface areas than do the tungsten-halogen low beams. Because smaller light sources result in more discomfort glare (presumably via greater luminance), the present finding suggests that the smaller illuminated area is one reason for drivers reporting more discomfort from HID lamps. An implication is that the increased discomfort from HID lamps could be reduced by increasing their illuminated surface area.

The Illuminated Surface Areas of HID and Tungsten-halogen Headlamps in the U.S.

Mary Lynn Buonarosa

This in-traffic study evaluated driving performance with and preference for HID low beams. Subjects drove two identical luxury sedans. One vehicle was equipped with HID low beams and the other with tungsten-halogen low beams. The main difference between the two beams was that the HID lamps provided more spread light. Driving performance was evaluated by analyzing steering frequencies. The hypothesis was that the wider beam pattern of the HID lamps would be beneficial by reducing the steering effort in the 0.3 to 0.6 Hz range, which has been used in previous studies as an index of steering-task difficulty. The main finding is that the wider HID beam pattern made lane maintenance less demanding, as measured by a reduction in the steering frequencies between 0.3 and 0.6 Hz. The implication is that HID headlamps may be beneficial to safety, because their wider beam pattern allows more of the limited information processing resources of drivers to be allocated to other tasks. When the subjects were not primed before driving to pay attention to the headlamps, they did not show, as a group, preference for either type of lamp. However, when they weretold to pay attention to the headlamps, they overwhelmingly preferred the HID lamps.

Driving Performance with and Preference for HID Headlamps

Y. Nakata

This analytical study compared the median beam pattern of a sample of 19 HID low beams manufactured for model year 2000 vehicles sold in the U.S. with a market-weighted median beam pattern of tungsten-halogen lamps for vehicles of the same model year. The results indicate that the HID lamps tended to provide wider beam patterns than did the tungsten-halogen lamps, which, in turn, should improve the visibility of pedestrians on curves and may make the lane-maintenance task less demanding. On right curves, there was an increase in glare illumination towards oncoming drivers, while on left curves there was a decrease in glare illumination. On straight roads, the HID lamps produced more illumination for pedestrians and road delineation on the left side of the road. This was also the case for the right side of the road, but only for the projector HID lamps; the nonprojector HID lamps produced less illumination at the relevant locations than did the tungsten-halogen lamps. Finally, on straight roads HID lamps produced less glare for oncoming drivers than did the tungstenhalogen lamps. The results for traffic-sign illumination varied with the location of the sign.HID lamps produce more light than do tungsten-halogen lamps. Consequently, they hold great promise for improving the nighttime safety of driving by improving the lowbeam light distribution. The present analysis indicates that this promise has already been partially met in the first generation of HID lamps on vehicles in the U.S.

Performance of the First Generation of HID Headlamps in the United States

Matthew P. Reed

Turn signals mounted on exterior rearview mirrors are increasingly being used as original equipment on passenger cars and light trucks. The potential for mirror-mounted turn signals (MMTS) to improve the geometric visibility of turn signals is examined in this paper. A survey of U.S. and UN-ECE regulations showed that the turn signals of a vehicle that is minimally compliant with U.S. regulations are not visible to a driver of a nearby vehicle in an adjacent lane. Measurements of mirror location and window geometry were made on 74 passenger cars and light trucks, including 38 vehicles with fender-mounted turn signals (FMTS). These data were combined with data on driver eye locations from two previous studies to assess the relative visibility of MMTS and conventional signals. Simulations were conducted to examine the potential for signals to be obstructed when a driver looks laterally through the passenger-side window. With a vehicle population that is fifty percent light trucks, MMTS are visible 52 percent more often than FMTS in this scenario. Based on the lateral visibility analysis, the optimal height for geometric visibility of a signal in the adjacent-vehicle scenario is 124 cm above the ground, approximately the average height of a light truck mirror. A plan-view eccentricity analysis showed that an MMTS is much closer to the viewing driver's forward-directed line of sight than rear-mounted turn signals when the viewing driver's vehicle is in or near the blind zone between the signaling driver's mirror and direct peripheral fields of view. MMTS can improve the geometric visibility of turn signals in the adjacent-vehicle scenario that is believed to precede many lane-change/merge crashes. Further research will be necessary to determine if improved geometric visibility is accompanied by improved detection of turn signals by viewing drivers, and whether improved detection of turn signals has important safety implications.

Michael J. Flannagan

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