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Modern roundabout facilities are increasing in number throughout North America and the world. Appropriate vehicle lighting, including the application of intelligent headlighting systems, might help support safe, efficient driving behavior while navigating through these new intersection types. We present the results of a field study conducted to compare different vehicle lighting systems in terms of drivers' ability to detect and identify pedestrian activity, under different amounts of illumination from fixed outdoor lighting systems. The results are compared to analytical predictions of visibility using a validated visual performance model.

Vehicle headlamps are essential for driver safety at night, and technological evolution of headlamps over several decades has brought substantial improvements to driver visibility and comfort. Nonetheless, glare remains an important concern among many in the driving public, perhaps even more so in North America, where requirements for headlamps differ from those in much of the rest of the world. In most of the world, headlamps producing higher luminous flux are required to have automatic leveling and cleaning systems, thought to help reduce glare. The arrival of headlamp systems in the worldwide marketplace with luminous flux values just below those triggering requirements for leveling and cleaning systems will bring new questions about the causes of and countermeasures for glare.

Rear signal lighting on vehicles has two primary functions: informing other drivers about the presence of a vehicle on the roadway, and alerting those other drivers to intentions of a vehicle's driver before actions such as turning or stopping occur. In the present paper, reports, articles and other technical literature, pertaining to rear lighting signal system photometric requirements and use of dynamic display features, are reviewed. The objective is to synthesize recommendations for configuring rear lighting in order to optimize systems for different ambient weather and lighting conditions, dirt accumulation, and warning functions. Research results from European, North American and Japanese contexts are discussed.

The present design standards for low beam headlamps offer significant flexibility regarding the distribution of light that they generate. Some headlamp systems produce significant amounts of foreground illumination, which increases the apparent brightness of the roadway surface close to the vehicle, and this increased brightness is seen as desirable by many individuals. Some individuals may prefer not only high but uniform foreground illumination. At almost any driving speed, however, any objects located in the visual foreground are too close to avoid with slowing or steering maneuvers. Further, published literature on the mechanisms for disability glare suggests that foreground illumination should have a negative impact in terms of the visibility of objects located well ahead in the visual field.

The present design standards for low beam headlamps offer significant flexibility regarding the distribution of light that they generate. Some headlamp systems produce significant amounts of foreground illumination, which increases the apparent brightness of the roadway surface close to the vehicle, and this increased brightness is seen as desirable by many individuals. Some individuals may prefer not only high but uniform foreground illumination. At almost any driving speed, however, any objects located in the visual foreground are too close to avoid with slowing or steering maneuvers. Further, published literature on the mechanisms for disability glare suggests that foreground illumination should have a negative impact in terms of the visibility of objects located well ahead in the visual field.

We summarize the development and initial deployment of a system that can be mounted along an intersection, curve, drive-in, or parking facility to efficiently gather relevant data about headlamp patterns that might relate to glare or visibility. The system can run autonomously to collect many vehicles per data collection period. The system includes a range finder to capture information when an approaching vehicle is at a specific location, a digital camera to store images of oncoming headlamp position (i.e., mounting height), two arrays of light sensors to measure the vertical headlamp illumination profile (e.g., angular position of headlamp beam cutoff or maximum luminous intensity), and a color-calibrated illuminance meter at the angular location of an oncoming driver's eyes. From the headlamp mounting height data and the vertical cutoff location data, an estimate of the headlamp aim distribution can be made.

In real world driving conditions, illumination from vehicle headlamps and, when present, from fixed roadway lighting combines to provide visibility for the driver. We present analyses of visibility along a representative roadway intersection scenario with median and market-weighted headlamp beam patterns including halogen and high intensity discharge headlamp beam patterns, and high beam headlamp beam patterns. Also investigated are interactions with the spatial extent of roadway lighting, either as part of a continuous lighting system or as a single roadway luminaire at the intersection junction, and the role of ambient illuminance from urban environments. The results of the analyses show the large influence of ambient illuminance from urban areas on the visibility of relevant targets, and show differential advantages of different headlamp beam patterns for different target locations where pedestrians might be encountered.

An experimental field investigation is described that compares off-axis (peripheral) visual performance between high-intensity discharge (HID) forward lighting and halogen systems. The goal of the investigation is to determine if the higher off-axis intensity levels combined with the spectral properties of HID lamps provide any benefits to visual performance over conventional tungsten halogen lamps. In this study three current production European headlamp systems, one HID and two halogen, are compared. These systems are used to illuminate a fixed scene. Subjects perform a visual tracking task, cognitively similar to driving, while simultaneously small targets located at various angles in the periphery are activated. Subjects release a switch upon detection and reaction times and missed signals are measured.

Peripheral visibility is an important aspect of driving but one that is not understood as robustly as on-axis visibility. The present paper summarizes results from a series of field studies investigating the effect of headlamp illumination and of oncoming headlamp glare on the speed and accuracy of response to small targets located in the visual periphery. These experiments used headlamp sets providing differing amounts of illumination on targets of varying reflectance, located throughout the field of view. Reaction times to the onset of targets and the percentage of missed targets were measured. The characteristics and locations of the targets and experimental geometry were similar in each study as were the subject demographic characteristics, so that results were very consistent among each of the studies.

Illumination from high intensity discharge (HID) headlamps differs from halogen headlamp illumination in two important ways: HID headlamps have higher overall light output and a spectral power distribution that differs from halogen headlamps. These differences have been hypothesized to result in superior visibility with HID headlamps and most particularly in the periphery. These same factors, though, have also been conjectured to result in increased glare for drivers facing HID headlamps in oncoming driving situations. The present paper outlines a series of experimental investigations using halogen, HID, and blue-filtered halogen illumination to measure their relative impact on discomfort glare and disability glare under conditions matching those that might be experienced by oncoming drivers at night. Discomfort glare is determined using the scale devised by de Boer; disability glare is determined by measuring subjects' contrast sensitivity under different lighting conditions.

Recent studies have shown that high-intensity discharge (HID) headlamps provide visual benefits to the vehicle operator that may lead to greater nighttime driving safety.[1] This paper is an extension of that work to further examine the role of beam pattern. An experimental field investigation is described that explores the visual performance aspects of HID forward lighting systems meeting North American beam pattern standards. This study further explores and quantifies the overall benefits of HID systems by direct comparison to conventional halogen systems. It examines and compares two systems producing typical Society of Automotive Engineers (SAE) J1383 beam patterns. Subjects perform a visual tracking task, cognitively similar to driving, while seated in the driver's seat of a test vehicle. Simultaneously, small targets located at various angles in the periphery are activated, with subjects releasing a switch upon detection so that reaction times can be measured.

Recent studies have shown that high-intensity discharge (HID) headlamps provide visual benefits to the vehicle operator that may lead to increased nighttime driving safety. An experimental field investigation is described that further investigates the visual performance aspects of HID forward lighting systems to isolate and examine the role of lamp spectral distribution under realistic nighttime driving conditions. This study examines lamp spectral distribution by direct comparison of HID source spectra to one that simulates a conventional halogen source. Two additional lamp spectra are also included in this study, a “cool” distribution with a high percentage of short wavelength visible light and a “warm” distribution with a high percentage of long wavelength visible light. Subjects perform a visual tracking task, cognitively similar to driving, while seated in the driver's seat of a test vehicle.

A research project has been completed to determine if commercially available blue coated lamps provide visual benefit for nighttime driving over standard tungsten halogen lamps. As an esthetic option, tungsten halogen lamps with an absorptive coating have been developed to mimic the appearance of HID lamps. The transmission of these coated lamp results in a continuous output spectrum, like standard tungsten halogen, but with a lower “yellow” content, giving an appearance similar to HID lamps. Aside from esthetic reasons for using blue coated lamps, there is also evidence that the spectral output may provide visual benefits over standard tungsten halogen lamps in nighttime driving. While driving at night, off-axis or peripheral vision is in the mesopic response range and the eye's sensitivity shifts towards shorter wavelengths or “blue” light.

Photometric performance specifications for vehicle headlamp specifications in North America are given in terms of luminous intensity values at various angular locations with the objective of providing sufficient illumination for forward visibility while controlling for glare toward oncoming and preceding vehicle drivers. Abundant evidence suggests that luminous intensity is an appropriate metric for characterizing the degree to which a headlamp can produce disability glare through veiling luminances under a wide range of viewing conditions. Notwithstanding that discomfort glare exhibits a differential spectral sensitivity from the photopic luminous efficiency function used to characterize light, luminous intensity does not always predict discomfort glare. For example, the luminance of the luminous element(s) can be more predictive of discomfort when headlamps are viewed from relative close distances.

Recent technological developments have begun to add a number of new configurations for vehicle forward lighting to the realm of possibility, including high-intensity discharge and light-emitting diode headlamps, and adaptive forward-lighting systems. These systems can offer substantial differences in performance and appearance from conventional filament-based headlamps that have been ubiquitous for many decades. These differences have not gone unnoticed by the U.S. driving public. A review of newspaper articles published during the past several years was conducted in order to assess public perceptions of vehicle headlamps in terms of their ability to support visibility and their impacts on headlamp glare.

Present standards for vehicle forward lighting specify two headlamp beam patterns: a low beam when driving in the presence of other nearby vehicles, and a high beam when there is not a concern for producing glare to other drivers. Adaptive lighting technologies such as curve lighting systems with steerable headlamps may be related to increments in safety according to the Insurance Institute for Highway Safety, but isolating the effects of lighting is difficult. Recent analyses suggest that visibility improvements from adaptive curve lighting systems might reduce nighttime crashes along curves by 2%-3%. More advanced systems such as adaptive high-beam systems that reduce high-beam headlamp intensity toward oncoming drivers are not presently allowed in the U.S. The purpose of the present study is to analyze visual performance benefits and quantify potential safety benefits from adaptive high-beam headlamp systems.

Many individuals believe that yellow headlights are preferable to white headlights when driving at night during a snowfall. Although evidence exists to support the claim that yellow light can be perceived as less “glaring” or “distracting” than white light of equal luminance, it is not clear whether backscattered light of different colors are differentially effective for driver comfort or for driver performance. This study investigates a potential mechanism that could support the supposed benefit of yellow headlamps for reducing the detrimental effects of backscattered light to drivers at night. The results suggest that under low light levels when the visual field is dominated by a dynamic field of visual “noise” (like that caused by backscattered light from falling snow), performance of a tracking task similar to driving is reduced in accordance with the scotopic (rod-stimulating) content of the visual noise.

A field study to measure peripheral visual performance under various headlamp conditions typical of halogen and high intensity discharge (HID) headlamps and including functions that could be incorporated in advanced forward-lighting systems (AFS), was conducted. The study simulated an approach of left- and right-hand turns. Targets of varying size were located at different locations along the edges of the curves, and different headlamp illumination conditions were used. Reaction times and missed targets were measured. The results were consistent with previously published studies showing a benefit of increased peripheral illumination commonly found in HID headlamps and with AFS systems on peripheral target detection.

Flashing emergency and warning lights are critical elements of public safety and traffic control during roadway incidents. These lights should not only alert drivers to their presence, but also should inform them of who and what is present on the scene, and should help to manage the responses of drivers as they navigate past the incident. First responder and driver safety depend upon all three of these functions, yet standards focus almost entirely on alerting drivers. A full-scale outdoor field study was carried out during daytime, during nighttime on dry pavement and during nighttime on wet pavement, using a mock-up roadside scene containing three police vehicles. The lights on the vehicles were adjusted to produce different levels of intensity, flash rate, and synchronization of lights across all three vehicles. In some cases, sequentially flashing lights were present.

Glare from oncoming vehicles while driving at night impairs visibility through the mechanism of scattered light in the eyes, which reduces the luminance contrast of objects in the field of view, and through the mechanism of increasing the visual adaptation level, which decreases visibility following glare exposure. Glare can also cause discomfort, which is most commonly assessed experimentally through the use of subjective rating scales. The present paper reports on an investigation of methods to assess glare's impact on driving behavior in a naturalistic setting. Vehicles belonging to drivers were instrumented with a photosensor to estimate the glare illuminance, as well as sensors for monitoring speed, acceleration, braking status, lane position and other attributes. Data from all of these instruments were collected and stored.