Heavy trucks, conspicuity treatment, and the decline of collision risk in darkness

In December 1992, Federal Motor Vehicle Safety Standard (FMVSS) 108, was amended to require conspicuity treatments on all heavy trailers manufactured after December 1, 1993. The standard was later modified and extended to tractors and older trailers such that by June 1, 2009 the entire fleet of tractors and semitrailers on United States roadways would reach full compliance with the regulation. To investigate the effect of the regulation, an analysis was conducted of the change in the odds that a fatal crash occurred in darkness, comparing scenarios in which the conspicuity treatment was likely to be influential to those in which the conspicuity treatment was likely to be irrelevant. From 1987 to 2009, the odds that a fatal collision involving a heavy truck occurred in darkness declined by 58% among the relevant crash scenarios, while little evidence of decline was found among the irrelevant scenarios. Disaggregations of crash scenario types suggest that the largest declines occurred in fatal rear end and angle collisions. A comparative analysis of light vehicles also found declines, although they were smaller and less sensitive to crash type. Similar but weaker trends were observed for nonfatal rear end collisions. The results are consistent with causal mechanisms that suggest that detection failure may be a significant contributor to the risk of striking a tractor-semitrailer in darkness, and that conspicuity treatments have significantly reduced this risk.The University of Michigan Industry Affiliation Program for Human Factors in Transportation Safetyhttp://deepblue.lib.umich.edu/bitstream/2027.42/89938/1/102820.pd

Risk of Fatal Rear-End Collisions: Is There More to It Than Attention?

Rear-end collisions predominantly occur in the daytime under clear, unobstructed viewing conditions and usually involve a lead vehicle that is stopped at the time of collision. These facts suggest that driver inattention plays a significant causal role in rear-end collisions, and mitigation efforts have therefore focused largely on development of warning technologies to alert drivers of an impending crash. However, we note that this pattern of crash data should not lead to the conclusion that drivers have special difficulty avoiding rear-end collisions in broad daylight. Nor should it be concluded that other “environmental” factors do not influence driving behavior to increase rear-end crash risk. Crash frequency is determined both by the inherent risk in the driving task and by the frequency of driver exposure to conditions in which a crash is possible. When exposure level is equated across conditions which differ in ambient light level, we find that rear-end collisions appear to be more than twice as likely in darkness than in daylight

Risk of Fatal Rear-End Collisions: Is There More to It Than Attention?

Rear-end collisions predominantly occur in the daytime under clear, unobstructed viewing conditions and usually involve a lead vehicle that is stopped at the time of collision. These facts suggest that driver inattention plays a significant causal role in rear-end collisions, and mitigation efforts have therefore focused largely on development of warning technologies to alert drivers of an impending crash. However, we note that this pattern of crash data should not lead to the conclusion that drivers have special difficulty avoiding rear-end collisions in broad daylight. Nor should it be concluded that other “environmental” factors do not influence driving behavior to increase rear-end crash risk. Crash frequency is determined both by the inherent risk in the driving task and by the frequency of driver exposure to conditions in which a crash is possible. When exposure level is equated across conditions which differ in ambient light level, we find that rear-end collisions appear to be more than twice as likely in darkness than in daylight

Driver Behavior as a Function of Ambient Light and Road Geometry

OBJECTIVES To determine how ambient light (day versus night) and road geometry affect driving behavior,especially the speeds that drivers choose when not constrained by lead vehicles.METHODSRecently, it has become technically easier to observe how people drive b offering them longtermuse of highly instrumented vehicles. Much of this type of work has been done in connectionwith large-scale field operational tests (FOTs) of various innovative vehicle systems. Theinformation obtained is in many ways complementary to information from observation of traffic.Traffic observation often provides information about a large number of drivers, but at a relativelycoarse level and in a spatially and temporally limited context (i.e., observing how a large numberof drivers negotiate a particular intersection). In contrast, long-term use of highly instrumentedvehicles is more restricted in terms of how many drivers can be observed, although the feasiblenumbers are now reasonably high. On the positive side, data from instrumented vehicles canoffer very detailed information about driving behavior over many miles and many days.In this paper, we present results from a database of driving behavior that was derived from arecent FOT for an adaptive cruise control (ACC) system (although the data used here are all fromphases of the study that involved only normal vehicle equipment). The FOT involved tenidentical cars that were instrumented for a variety of types of data. The most important data forpresent purposes were: speed, yaw rate, location from the Global Positioning System (GPS), andpresence or absence of a lead vehicle within about 100 m based on the forward-looking sensorsof the ACC system. The instrumented cars were driven by a total of 108 participants, each ofwhom was given a car to use as his or her own vehicle in normal driving for either two or fiveweeks. The participants were sampled from licensed drivers in southeastern Michigan, andrepresented a wide range of age and driving experience.RESULTSResults will be reported in terms of speed as a function of horizontal road curvature in light anddark conditions, and as a function of driver age and gender, all for situations in which there is nolead vehicle within about 100 m. CONCLUSIONSCurrent evidence about headlighting suggests that drivers’ ability to see and negotiate theroadway is virtually unaffected by differences in ambient light, although their ability to perceiveand avoid objects on the road, such as pedestrians, is greatly reduced when headlamps are themain source of light. There is also evidence that drivers do not markedly reduce their speed inconditions of low ambient light. The current analysis allows us to determine how drivers react tospecific road geometries in light and dark conditions. This has implications for how well drivers’perceptual abilities match their driving behavior, and also for assessing the potential benefit of avariety of innovative headlighting systems that are currently being designed to adapt in variousways to vehicle speed and road geometry

Driver Behavior as a Function of Ambient Light and Road Geometry

OBJECTIVES To determine how ambient light (day versus night) and road geometry affect driving behavior,especially the speeds that drivers choose when not constrained by lead vehicles.METHODSRecently, it has become technically easier to observe how people drive b offering them longtermuse of highly instrumented vehicles. Much of this type of work has been done in connectionwith large-scale field operational tests (FOTs) of various innovative vehicle systems. Theinformation obtained is in many ways complementary to information from observation of traffic.Traffic observation often provides information about a large number of drivers, but at a relativelycoarse level and in a spatially and temporally limited context (i.e., observing how a large numberof drivers negotiate a particular intersection). In contrast, long-term use of highly instrumentedvehicles is more restricted in terms of how many drivers can be observed, although the feasiblenumbers are now reasonably high. On the positive side, data from instrumented vehicles canoffer very detailed information about driving behavior over many miles and many days.In this paper, we present results from a database of driving behavior that was derived from arecent FOT for an adaptive cruise control (ACC) system (although the data used here are all fromphases of the study that involved only normal vehicle equipment). The FOT involved tenidentical cars that were instrumented for a variety of types of data. The most important data forpresent purposes were: speed, yaw rate, location from the Global Positioning System (GPS), andpresence or absence of a lead vehicle within about 100 m based on the forward-looking sensorsof the ACC system. The instrumented cars were driven by a total of 108 participants, each ofwhom was given a car to use as his or her own vehicle in normal driving for either two or fiveweeks. The participants were sampled from licensed drivers in southeastern Michigan, andrepresented a wide range of age and driving experience.RESULTSResults will be reported in terms of speed as a function of horizontal road curvature in light anddark conditions, and as a function of driver age and gender, all for situations in which there is nolead vehicle within about 100 m. CONCLUSIONSCurrent evidence about headlighting suggests that drivers’ ability to see and negotiate theroadway is virtually unaffected by differences in ambient light, although their ability to perceiveand avoid objects on the road, such as pedestrians, is greatly reduced when headlamps are themain source of light. There is also evidence that drivers do not markedly reduce their speed inconditions of low ambient light. The current analysis allows us to determine how drivers react tospecific road geometries in light and dark conditions. This has implications for how well drivers’perceptual abilities match their driving behavior, and also for assessing the potential benefit of avariety of innovative headlighting systems that are currently being designed to adapt in variousways to vehicle speed and road geometry

Visual effects of blue-tinted tungsten-halogen headlamp bulbs

Manufacturers have recently introduced several types of tungsten-halogen headlamp bulbs that have been filtered to produce bluish tints. Some informal reports suggest that the differences in spectral power distribution due to the tinting enhance visual performance and reduce fatigue; others suggest that they simply provide esthetic benefits. In this study, we investigate the effect of three headlamp types (a standard tungsten-halogen lamp, a broadly filtered blue-tinted lamp, and a neodymium-filtered blue-tinted lamp) on two aspects of vision (discomfort glare judgments and the luminance threshold for target detection). Consistent with prior studies, the results show that discomfort glare ratings increase as chromaticity moves toward the blue range. No evidence was observed that target detection is enhanced with blue headlamps for either peripherally viewed or centrally viewed targets. However, when deeply colored light sources (beyond the range of nominal white that headlamps are required to meet) were introduced into the detection task, differences in spectral sensitivity were observed in the near-periphery.Michigan University, Ann Arbor, Industry Affiliation Program for Human Factors in Transportation Safetyhttp://deepblue.lib.umich.edu/bitstream/2027.42/49444/1/UMTRI-2001-9.pd

Just noticeable differences for low-beam headlamp intensities

A recent study by Huey, Dekker, and Lyons (1994) concluded that a difference between two signal lamp intensities of less than 25% cannot be detected reliably by most drivers. Consequently, Huey et al. recommended that an intensity difference of 25% be used as a criterion for inconsequential noncompliance with federal regulations for signal lamps. The present study was designed to evaluate just noticeable differences for glare intensities of oncoming low-beam headlamps. The results of this study indicate that, under controlled conditions, just noticeable differences in the low-beam headlighting context are between 11% and 19%. In real-world conditions, just noticeable differences would probably be somewhat larger. Therefore, the recommendation by Huey et al. of using 25% as a criterion for inconsequential noncompliance of signal lamps is also about right for low-beam headlamps, at least with respect to how headlamps themselves are perceived by other drivers (such as discomfort glare). The 25% value may also apply with respect to how headlamps affect the ability of drivers to see illuminated objects, but further research on that issue would be desirable.Michigan University, Ann Arbor, Industry Affiliation Program for Human Factors in Transportation Safetyhttp://deepblue.lib.umich.edu/bitstream/2027.42/49359/1/UMTRI-97-4.pd

Relationships among driver age, vehicle cost, and fatal nighttime crashes

The ratio of crashes in darkness to those occurring in daylight has been used to assess the relative sensitivity of certain risk factors to ambient light level. When applied in a way that maintains control over exposure level, use of dark/light ratios can be helpful in identifying crash factors that are particularly sensitive to darkness. For example, during daylight saving time changeovers, dark/light ratios have been used to demonstrate the high vulnerability of pedestrians in darkness. In this report, we examine the application of the night/day ratio to evaluate changes in crash risk in darkness associated with vehicle characteristics. We find that correlations between driver age, vehicle cost, and patterns of driving suggest that links between vehicle equipment and crash risk in darkness cannot be asserted without also taking these factors into account. Younger drivers drive proportionally more miles at night, and show proportionally higher risk of fatal crash involvement at night than older drivers. Young drivers also drive proportionately less expensive vehicles than middle-aged and older drivers, and they drive an increasing proportion of originally expensive vehicles as the age of the vehicle increases. These changes in driver age demographics must be considered when evaluating nighttime crash countermeasures.The University of Michigan Industry Affiliation Program for Human Factors in Transportation Safetyhttp://deepblue.lib.umich.edu/bitstream/2027.42/61910/1/102028.pd

Photometric indicators of headlamp performance

The visibility of an object is largely determined by the relative contrast between the object and its background. Thus, it might be assumed that without consideration of environmental conditions surrounding a target illuminated by a headlamp, target visibility may not be accurately assessed. That is, methods that consider only illuminance characteristics of headlamps (e.g., distribution and intensity of light) may assess headlamp performance differently from methods that include roadway and viewing conditions in the appraisal. In this report, headlamp performance ratings are first generated using CHESS, a software application that determines visibility by simulating headlamp illumination, roadway, and target characteristics, using target contrast. The CHESS ratings were then compared with ratings obtained by two alternative illuminance-based ratings methods. The first method, the lux-area method, computes road area at or above an established lux threshold. The second method, the distant-light method, computes the average lux level within a predefined forward road area centered on the midline of the vehicle. Twenty-two tungsten halogen (TH) headlamps were evaluated using each method and their performance ratings were compared with the CHESS ratings. The simple illuminance-based measures were found to be closely correlated with the CHESS ratings. The distant-light method produced the highest correlations.The University of Michigan Industry Affiliation Program for Human Factors in Transportation Safetyhttp://deepblue.lib.umich.edu/bitstream/2027.42/63098/1/102301.pd

Vehicle kinematics in turns and the role of cornering lamps in driver vision

SAE Recommended Practice J852 and ECE Regulations 119 and 48 for cornering lamps were compared. Photometric points described in each specification were then compared to naturalistic low-speed turn trajectories produced by 87 drivers. Future locations of a vehicle engaged in a turn were calculated based on the vehicle’s momentary position and speed, and the calculated time required to bring a vehicle to a complete stop. The angular offset and distance separating current and future positions were compiled to produce a map of useful preview positions—that is, positions relative to the current position of the vehicle that are far enough away to allow a driver to successfully stop if an object is first seen there. The distribution of preview positions shows strong concentrations between 30 and 35 degrees to the right or left of the current direction of travel. Geometric characteristics of this distribution were then compared to the geometry implied by the photometric minimum points indicated in the two specifications. Implications for path illumination during turns were discussed.The University of Michigan Industry Affiliation Program for Human Factors in Transportation Safetyhttp://deepblue.lib.umich.edu/bitstream/2027.42/85359/1/102757.pd