Eric C. Traube

Effects of retroreflector positioning on nighttime recognition of pedestrians

This field study investigated potential effects of retroreflector positioning on recognition of nighttime pedestrians. The subjects task was to press a response button whenever he/she recognized a pedestrian on or alongside the road, while in a car with low-beam lamps on that was driven at a constant speed on a dark road. The results showed that each retroreflector configuration yielded significantly longer recognition distances than the no-retroreflector configuration. More importantly, the retroreflective markings attached to the limbs led to significantly longer (about 60-80%) recognition distances than when the retroreflective markings were attached to the torso. Furthermore, a pedestrian was more recognizable while crossing the road than while approaching the subject vehicle, except for configurations involving no retroreflective markings.

A Market-Weighted Description of Low-Beam Headlighting Patterns in the U.S.

This study provides updated, market-weighted photometric information about current European low-beam headlamps for model year 2003. The sample included 20 headlamps manufactured for use on the 20 best-selling passenger vehicles in 19 European countries. The vehicles sampled represent 47% of all vehicles sold in these countries. These lamps were purchased directly from vehicle dealerships and the photometric information for each lamp was weighted by the sales figures for the corresponding vehicle. The results are presented in tabular form for the 25th-percentile, 50th-percentile and the 75th-percentile luminous intensities. The results are also presented in graphic form for the median luminous intensities as well as for the median illuminance incident on vertical surfaces at various locations on the roadway. The data presented in this report should provide valid estimates of the luminous intensities that can be expected at various angles with respect to the headlamp axes of low-beam tungsten-halogen headlamps. This data could be used to calculate the expected illuminance reaching targets with known geometric relationships to the headlamps, such as traffic signs, road delineation, or rearview mirrors on receding vehicles.

Effects of Overall Low-Beam Intensity on Seeing Distance in the Presence of Glare

Previous studies have demonstrated that current low-beam headlamps do not provide adequate seeing distance for safety. Could this situation be improved by providing more total light from low-beam headlamps, leaving the relative distribution of light unchanged? Although such a proposal is probably not the best practical solution, it is important to consider some of the visual consequences of a general increase in light to analyze the overall problem of low-beam headlighting. In a nighttime field study we measured seeing distance in the presence of glare as a function of headlamp intensity, always varying the intensity of the seeing light and glare light by the same proportion. Increasing intensity by a factor of about 3.8 increased seeing distance by about 17% for both young and old drivers. This result is consistent with predictions from quantitative vision modeling using veiling luminance to represent the disabling effects of glare. We also collected subjective estimates of discomfort glare and found, as expected, that the higher intensities produced substantially more discomfort. Our findings suggest that, if objective visual performance is the only criterion, there is no clear upper limit to how intense low-beam headlamps should be. However, there may be a level at which people simply will not tolerate the subjectively discomforting effects of glare, or at which glare indirectly affects objective performance through its effects on subjective comfort. Because subjective discomfort, rather than objective visual performance, may be the limiting consideration for setting maximum glare levels, more research should be done to understand the nature and consequences of discomfort glare, including possible effects of subjective comfort on objective visual behavior.

Effects of turn-signal colour on reaction times to brake signals

This laboratory experiment was designed to compare reaction times to brake signals when they appear with red or yellow turn signals. The subjects task was to respond as quickly as possible to the onset of peripherally presented brake lamps, while engaged in a central tracking task. There were three lamp conditions: brake lamps alone, brake lamps while turn signal was on, and a turn-signal lamp alone. The results showed that yellow turn signals, in comparison to red turn signals, led to significantly shorter reaction times to brake signals.

DRIVER PERCEPTUAL ADAPTATION TO NONPLANAR REARVIEW MIRRORS

This study examined perceptual adaptation to nonplanar (spherical convex and aspheric) rearview mirrors. Subjects made magnitude estimates of the distance to a car seen in a rearview mirror. Three different mirrors were used: plane, aspheric (with a large spherical section having a radius of 1400 mm), and simple convex (with a radius of 1000 mm). Previous research relevant to perceptual adaptation to nonplanar mirrors was reviewed. It was argued that, in spite of some cases of explicit interest in the process of learning to use nonplanar mirrors, previous research has not adequately addressed the possibility of perceptual adaptation. The present experiment involved three phases: (1) a pretest phase in which subjects made distance judgments but received no feedback, (2) a training phase in which they made judgments and did receive feedback, and (3) a posttest phase with the same procedure as the pretest phase. Initially subjects showed substantial overestimation of distance with the convex mirror relative to the aspheric mirror, and with the aspheric mirror relative to the plane mirror. At the beginning of the training phase, overestimation with the convex mirror quickly diminished, but after about one hour of experience the convex and aspheric mirrors still showed significant overestimation relative to the plane mirror. The present results demonstrate the existence of a rapid, but incomplete, form of adaptation. Whether there is a further mechanism that might operate over a longer time, but lead to more complete adaptation, is an open question that should be addressed by further research. Future research should also address the question of what forms of experience or training are most conducive to adaptation. If substantial adaptation is indeed possible, the use of nonplanar rearview mirrors would be strongly encouraged.

Daytime veiling glare and driver visual performance: Influence of windshield rake angle and dashboard reflectance

Abstract Reflections of the top of the dashboard seen in the windshield can result in disability glare because these reflections reduce the contrast of objects in the road scene. This phenomenon, which occurs mainly in direct sunlight, is due to the veiling luminance of the reflected sunlight being superimposed on the image of the road scene. The amount of veiling glare is influenced by the windshield rake angle and the dashboard reflectance. A field experiment under controlled sunlight conditions was performed. The independent variables included windshield rake angle, reflectance of the top of the dashboard, and subject age. The subjects were asked to detect pedestrian dummies having either high or low contrast against the background. Reaction times to the high-contrast pedestrian and misses of the low-contrast pedestrian were used as the main dependent variables. The results showed that both windshield rake angle and dashboard reflectance affected visual performance. Visual performance decreased with larger windshield rake angles and with higher dashboard-top reflectance. During those conditions, subjects needed more time to detect objects, and they had more misses in detecting low-contrast objects. The effect was particularly pronounced if a large rake angle was combined with a high dashboard reflectance, and older subjects were more affected by reductions in contrast then were younger subjects.

Color identification in the visual periphery: consequences for color coding of vehicle signals

In this field study we investigated the efficiency of color coding for peripheral identification of vehicle signals. Specifically, the study dealt with identification of stimuli as yellow or red when presented at intensities corresponding to typical turn-signal lamps and side-marker lamps. Turn-signal lamps were studied both during bright, sunny conditions and at night, whereas side-marker lamps were studied at night only. We used two yellow stimuli and two red stimuli. For each color category, one stimulus was relatively far from the contrasting color category and the other stimulus was relatively near. Four viewing angles were used: 0°, 10°, 20°, and 30° from visual fixation. We tested 28 participants ranging in age from 21 to 78 years. Nighttime identification of colors was perfect at all viewing angles for stimuli representing turn-signal lamps. On the other hand, strong effects of viewing angle were found for turn-signals in the daytime and for side-marker lamps at night. Although in these 2 conditions performance deteriorated for stimuli in both color categories, it did so more for the red stimuli. This finding is consistent with the previously reported finding that peripherally presented red stimuli often appear yellow. The findings imply that coding signals yellow and red is not sufficient for their peripheral identification under the 2 most difficult conditions tested (turn signals during bright daytime and side-marker lamps during nighttime). To the extent that peripheral discriminability is important in actual driving, efficient signaling should rely on other coding parameters (e.g., intensity, and flashing vs. steady burning).

Do changes in voltage result in proportional changes throughout headlamp beam pattern

This study evaluated the effects of voltage changes on beam patterns of low-beam headlamps. Seven different types of filament lamps were tested. The voltages used were 12.0, 12.8 and 13.5V. The photometry was performed from 20° left to 20° right, and from 5° down to 5° up, all in steps of 0.5°. The main finding of this study is that, for all seven lamps tested, voltage changes between 12.0V and 13.5V caused light output to change by the same proportion throughout the beam pattern. Therefore, for filament lamps, it is reasonable to use a single constant for all values in a beam pattern when converting a headlighting specification at one voltage to a specification at a different voltage, at least if the voltages in question are between 12.0 V and 13.5 V. The constants obtained across the seven lamps tested were similar to each other. Furthermore, these constants were in general agreement with the constants derived using the standard IES formula relating light-output changes to voltage changes.

Fog Lamps: Frequency of Installation and Nature of Use

The goal of this study was to provide information about the frequency of installation and use of fog lamps. Two surveys were performed. In the first one, installation of fog lamps was estimated by a survey of parked vehicles in two large shopping centers. The second survey studied the usage of fog lamps during daytime and nighttime, under clear, rainy, or foggy conditions. In this survey, an observer in a moving vehicle noted the types of lamps that were energized on the fronts of oncoming vehicles, and whether fog lamps were installed at all.

On-the-Road Visual Performance with Electrochromic Rearview Mirrors

The study was part of a series of studies on variable-reflectance rearview mirrors. Previous work included laboratory studies of human visual performance, field collection of photometric data, and mathematical modeling of the visual benefits of variable-reflectance mirrors. The authors extended that work in this study by collecting photometric and human performance data while subjects drove in actual traffic. Results indicated that variable-reflectance mirrors provided substantial reduction in discomfort glare without a measurable reduction in subjective ratings of rearward seeing ability. No major improvements were caused in forward seeing. The present study is inconclusive with respect to the benefits of a variable-reflectance driver-side mirror relative to a fixed-reflectance mirror with 50-percent reflectance. The reason for this is that the particular driver-side mirror used in this study became noticeably green in the low-reflectivity state, and thus low reflectivity was confounded with a color change. The effect of the driver-side mirror should be clarified by further research.