Pedestrian Crossing Decisions in Virtual Environments: Behavioral Validity in CAVEs and Head-Mounted Displays.

OBJECTIVE: To contribute to the validation of virtual reality (VR) as a tool for analyzing pedestrian behavior, we compared two types of high-fidelity pedestrian simulators to a test track. BACKGROUND: While VR has become a popular tool in pedestrian research, it is uncertain to what extent simulator studies evoke the same behavior as nonvirtual environments. METHOD: An identical experimental procedure was replicated in a CAVE automatic virtual environment (CAVE), a head-mounted display (HMD), and on a test track. In each group, 30 participants were instructed to step forward whenever they felt the gap between two approaching vehicles was adequate for crossing. RESULTS: Our analyses revealed distinct effects for the three environments. Overall acceptance was highest on the test track. In both simulators, crossings were initiated later, but a relationship between gap size and crossing initiation was apparent only in the CAVE. In contrast to the test track, vehicle speed significantly affected acceptance rates and safety margins in both simulators. CONCLUSION: For a common decision task, the results obtained in virtual environments deviate from those in a nonvirtual test bed. The consistency of differences indicates that restrictions apply when predicting real-world behavior based on VR studies. In particular, the higher susceptibility to speed effects warrants further investigation, since it implies that differences in perceptual processing alter experimental outcomes. APPLICATION: Our observations should inform the conclusions drawn from future research in pedestrian simulators, for example by accounting for a higher sensitivity to speed variations and a greater uncertainty associated with crossing decisions.

Young and older adult pedestrians' behavior when crossing a street in front of conventional and self-driving cars.

Self-driving vehicles are gradually becoming a reality. But the consequences of introducing such automated vehicles (AVs) into current road traffic cannot be clearly foreseen yet, especially for pedestrian safety. The present study used virtual reality to examine the pedestrians' crossing behavior in front of AVs as compared to conventional cars (CVs). Thirty young (ages 21-39) and 30 older (ages 68-81) adults participated in a simulated street-crossing experiment allowing for a real walk across an experimental two-way street. Participants had to cross (or not cross) in mixed traffic conditions where highly perceptible AVs always stopped to let them cross, while CVs did not brake to give them the right of way. Available time gap (from 1 to 5 s), approach speed (30 or 50 km/h), and the lane in which the cars were approaching (near and/or far lane of the two-way street) were varied. The results revealed a significantly higher propensity to cross the street, at shorter gaps, when AVs gave way to participants in the near lane while CVs were approaching in the far lane, leading to more collisions in this condition than in the others. These risky decisions were observed for both young and older participants, but much more so for the older ones. The results also indicated hesitation to cross in front of an AV in both lanes of the two-way street, with later initiations and longer crossing times, especially for the young participants and when the AVs were approaching at a short distance and braked suddenly. This study highlights the potential risks for pedestrians of introducing AVs into current road traffic, complicating the street-crossing task for young and older people alike. Future studies should look further into the role of repeated practice and trust in AVs. The design of these vehicles must also be addressed. Some practical recommendations are provided.

Improving motorcycle motion perception by using innovative motorcycle headlight configurations: Evidence from simulator and test-track experiments.

Many motorcycle accidents occur at intersections and are caused by other vehicle drivers who misperceive the speed and time-to-arrival of an approaching motorcycle. The two experiments reported here tested different motorcycle headlight configurations likely to counteract this perceptual failure. In the first experiment, conducted on a driving simulator, car drivers turned left in front of cars and motorcycles approaching an intersection under nighttime lighting conditions. The motorcycles were equipped with either a standard white central light, or one of three vertical configurations of white and yellow lights. The results showed that the standard configuration led to significantly more unsafe accepted gaps than the vertical configurations. In the second experiment, conducted on a test track using a similar task, the most promising motorcycle headlight configuration, i.e., the vertical yellow-white light arrangement (one central white light, plus one yellow light on the helmet and two yellow lights on the fork) was evaluated and compared to a standard configuration and a car. The vertical yellow-white headlight configuration again provided significant safety benefits as compared to the standard configuration. These findings demonstrate that motorcycle safety can be improved by headlight ergonomics that accentuate the vertical dimension of motorcycles. They also suggest that the driving simulator is a valid tool for conducting research on motorcycle headlight design.

Analysis of Street-Crossing Behavior: Comparing a CAVE Simulator and a Head-Mounted Display among Younger and Older Adults.

Interactive pedestrian simulators have become a valuable research tool for investigating street-crossing behavior and developing solutions for improving pedestrian safety. There are two main kinds of pedestrian simulators: one uses a technology based on rear-projection screens (Cave Automatic Virtual Environment, or CAVE), the other a head-mounted display (HMD). These devices are used indiscriminately, regardless of the research objective, and it is not yet known whether they are equally effective for studying street crossing. The present study was aimed at comparing the street crossing behavior and subjective evaluations of younger and older adult pedestrians when they are using a CAVE-like or HMD-based (HTC Vive Pro) pedestrian simulator. Thirty younger adults and 25 older adults performed 36 street-crossing trials (combining different speeds, two-way traffic conditions, and gap sizes) on each of the two types of simulators. The results indicated that participants in the HMD condition crossed the street significantly more often (58.6 %) than in the CAVE condition (42.44%) and had shorter safety margins. The most striking difference pertained to crossing initiation, which occurred considerably earlier (1.78 s) in the HMD condition than in the CAVE condition. Synchronization of crossing initiation with oncoming traffic was not as good in the CAVE condition because visual information in front of the pedestrian was missing due to the absence of ground projection. In both simulators, older adults caused more collisions than did younger ones, had shorter safety margins, and a slower crossing speed. Hence, the HMD reproduced classical age-related differences in most street-crossing behaviors already found on the CAVE. Usually observed speed effects were also found for both simulators. Neither cybersickness nor any adverse effects on stereoacuity or postural balance were found for either simulator. The HMD produced a higher level of presence and preference than the CAVE did. These findings provide evidence that HMDs have a clear potential for studying pedestrian behaviour.

Improving motorcycle conspicuity through innovative headlight configurations.

Most motorcycle crashes involve another vehicle that violated the motorcycle's right-of-way at an intersection. Two kinds of perceptual failures of other road users are often the cause of such accidents: motorcycle-detection failures and motion-perception errors. The aim of this study is to investigate the effect of different headlight configurations on motorcycle detectability when the motorcycle is in visual competition with cars. Three innovative headlight configurations were tested: (1) standard yellow (central yellow headlight), (2) vertical white (one white light on the motorcyclist's helmet and two white lights on the fork in addition to the central white headlight), and (3) vertical yellow (same configuration as (2) with yellow lights instead of white). These three headlight configurations were evaluated in comparison to the standard configuration (central white headlight) in three environments containing visual distractors formed by car lights: (1) daytime running lights (DRLs), (2) low beams, or (3) DRLs and low beams. Video clips of computer-generated traffic situations were displayed briefly (250ms) to 57 drivers. The results revealed a beneficial effect of standard yellow configuration and the vertical yellow configuration on motorcycle detectability. However, this effect was modulated by the car-DRL environment. Findings and practical recommendations are discussed with regard to possible applications for motorcycles.

Review of safety and mobility issues among older pedestrians.

Although old people make up an extremely vulnerable road-user group, older pedestrians' difficulties have been studied less extensively than those of older drivers, and more knowledge of this issue is still required. The present paper reviews current knowledge of older-adult problems with the main components of pedestrian activity, i.e., walking and obstacle negotiation, wayfinding, and road crossing. Compared to younger ones, old pedestrians exhibit declining walking skills, with a walking speed decrease, less stable balance, less efficient wayfinding strategies, and a greater number of unsafe road crossing behaviors. These difficulties are linked to age-related changes in sensorial, cognitive, physical, and self-perception abilities. It is now known that visual impairment, physical frailty, and attention deficits have a major negative impact on older pedestrians' safety and mobility, whereas the roles of self-evaluation and self-regulation are still poorly understood. All these elements must be taken into consideration, not only in developing effective safety interventions targeting older pedestrians, but also in designing roads and cars. Recent initiatives are presented here and some recommendations are proposed.

Improving car drivers' perception of motorcycle motion through innovative headlight configurations.

The most frequent cause of motorcycle accidents occurs when another vehicle violates the motorcycle's right-of-way at an intersection. In addition to detection errors, misperception of the approaching motorcycle's speed and time-to-arrival is another driver error that accounts for these accidents, although this error has been studied less often. Such misperceptions have been shown to be related to the small size of motorcycles and to their small angular velocity when approaching. In two experiments we tested the impact of different motorcycle headlight configurations in various ambient lighting conditions (daytime, dusk, and nighttime). The participants drove on a driving simulator and had to turn left across a line of vehicles composed of motorcycles and cars. The motorcycles were approaching at different speeds and were equipped with either a "standard" headlight, a "horizontal" configuration (added to the standard headlight were two lights on the rearview mirrors so as to visually increase the horizontal dimension of the motorcycle), a "vertical" configuration (one light on the rider's helmet and two lights on the fork were added to the standard headlight so as to increase the vertical dimension of the motorcycle), or a "combined" configuration (combining the horizontal and vertical configurations). The findings of the first experiment in nighttime conditions indicated that both the vertical and combined configurations significantly increased the gap car drivers accepted with respect to the motorcycle as compared to the standard configuration, and that the accepted gaps did not differ significantly from those accepted for cars. The advantage of the vertical and combined configurations showed up especially when the motorcycle's approach speed was high. The findings of the second experiment in dusk and daytime conditions indicated similar patterns, but the headlight-configuration effect was less pronounced at dusk, and nonsignificant during the day. The results are discussed with regards to possible applications for motorcycles.

Crossing a two-way street: comparison of young and old pedestrians.

INTRODUCTION: Choosing a safe gap in which to cross a two-way street is a complex task and only few experiments have investigated age-specific difficulties. METHOD: A total of 18 young (age 19-35), 28 younger-old (age 62-71) and 38 older-old (age 72-85 years) adults participated in a simulated street-crossing experiment in which vehicle approach speed and available time gaps were varied. The safe and controlled simulated environment allowed participants to perform a real walk across an experimental two-way street. The differences between the results for the two lanes are of particular interest to the study of visual exploration and crossing behaviors. RESULTS: The results showed that old participants crossed more slowly, adopted smaller safety margins, and made more decisions that led to collisions than did young participants. These difficulties were found particularly when vehicles approached in the far lane, or rapidly. Whereas young participants considered the time gaps available in both lanes to decide whether to cross the street, old participants made their decisions mainly on the basis of the gap available in the near lane while neglecting the far lane. CONCLUSIONS: The present results point to attentional deficits as well as physical limitations in older pedestrians. Several practical and have implications in terms of road design and pedestrian training are proposed.

Arrival-time judgments on multiple-lane streets: The failure to ignore irrelevant traffic.

How do road users decide whether or not they have enough time to cross a multiple-lane street with multiple approaching vehicles? Temporal judgments have been investigated for single cars approaching an intersection; however, close to nothing is known about how street crossing decisions are being made when several vehicles are simultaneously approaching in two adjacent lanes. This task is relatively common in urban environments. We report two simulator experiments in which drivers had to judge whether it would be safe to initiate street crossing in such cases. Matching traffic gaps (i.e., the temporal separation between two consecutive vehicles) were presented either with cars approaching on a single lane or with cars approaching on two adjacent lanes, either from the same side (Experiment 1) or from the opposite sides (Experiment 2). The stimuli were designed such that only the shortest gap was decision-relevant. The results showed that when the two gaps were in sight simultaneously (Experiment 1), street-crossing decisions were also influenced by the decision-irrelevant longer gap. Observers were more willing to cross the street when they had access to information about the irrelevant gap. However, when the two gaps could not be seen simultaneously but only sequentially (Experiment 2), only the shorter and relevant gap influenced the street-crossing decisions. The results are discussed within the framework of perceptual averaging processes, and practical implications for road safety are presented.

Measuring the effect of the rainfall on the windshield in terms of visual performance.

Driving through rain results in reduced visual performance, and car designers have proposed countermeasures in order to reduce the impact of rain on driving performance. In this paper, we propose a methodology dedicated to the quantitative estimation of the loss of visual performance due to the falling rain. We have considered the rain falling on the windshield as the main factor which reduces visual performance in driving. A laboratory experiment was conducted with 40 participants. The reduction of visual performance through rain was considered with respect to two driving tasks: the detection of an object on the road (contrast threshold) and reading a road sign. This experiment was conducted in a laboratory under controlled artificial rain. Two levels of rain intensity were compared, as well as two wiper conditions (new and worn), while the reference condition was without rain. The reference driving situation was night driving. Effects of both the rain level and the wipers characteristics were found, which validates the proposed methodology for the quantitative estimation of rain countermeasures in terms of visual performance.

Influence of front light configuration on the visual conspicuity of motorcycles.

A recent study (Cavallo and Pinto, 2012) showed that daytime running lights (DRLs) on cars create "visual noise" that interferes with the lighting of motorcycles and affects their visual conspicuity. In the present experiment, we tested three conspicuity enhancements designed to improve motorcycle detectability in a car-DRL environment: a triangle configuration (a central headlight plus two lights located on the rearview mirrors), a helmet configuration (a light located on the motorcyclist's helmet in addition to the central headlight), and a single central yellow headlight. These three front-light configurations were evaluated in comparison to the standard configuration (a single central white headlight). Photographs representing complex urban traffic scenes were presented briefly (for 250ms). The results revealed better motorcycle-detection performance for both the yellow headlight and the helmet configuration than for the standard configuration. The findings suggest some avenues for defining a new visual signature for motorcycles in car-DRL environments.

Functional declines as predictors of risky street-crossing decisions in older pedestrians.

The experiment investigated the extent to which risky street-crossing decisions by older pedestrians can be explained by declines in functional abilities. Sixteen young (age 20-35), 17 younger-old (age 60-67), and 18 older-old (age 70-84) participants carried out a street-crossing task in a simulated two-way road environment and took a battery of tests assessing perceptual, cognitive, and motor abilities. Older-old pedestrians were more likely than young and younger-old participants to make decisions that would have led to collisions with approaching cars, especially when traffic coming from two directions was approaching at a high speed. Regression analyses identified several functional performance measures as predictors of these dangerous choices. Walking speed, which determined the time needed to cross, was shown to play the most important role. Time-to-arrival estimate, which informed the pedestrians about the time available for crossing, was found to be the second most predictive factor. Visual processing speed and visual attention abilities assessed via the UFOV® Test also came into play, allowing participants to focus their attention on the relevant available information and to make timely, correct decisions. Attention shifting was the fourth significant predictor, allowing pedestrians to adapt their crossing strategy to the oncoming road-traffic information. The results suggest that the greater risk of being involved in a collision as age increases calls for a multi-dimensional explanation combining age-related physical, perceptual, and cognitive performance declines. These findings have implications for improving older pedestrians' safety in terms of speed limits, road design, and training.

The effects of age and traffic density on street-crossing behavior.

Past research has shown that road users accept shorter time gaps when the waiting time/number of vehicles they let pass before attempting to merge into the traffic increases. While elderly pedestrians are known to be an extremely vulnerable group of road users, very few studies dealt with the effect of environmental constraints and crossing complexity on this population's safety. The present study aimed at determining whether or not street-crossing decisions and behavior of younger and older pedestrians were differently affected by a traffic flow. In an interactive street-crossing task, we assessed whether mean time gap and crossing decisions depended on the position of the gap pedestrians selected into the traffic stream. Results revealed that irrespective of their age pedestrians accepted a smaller time gap when they chose the second interval of the traffic compared to the first one. Contrasting with previous hypotheses, this traffic-related behavior was not accompanied by an increase in the decisions risk. The findings also showed that the transition threshold from rejecting to accepting time gaps was shorter when the second interval was selected compared to the first one. This increment in task constraints might help younger and older pedestrians alike to perceive action possibilities more accurately and to be better attuned to traffic conditions by comparing gaps between each other. This opens an interesting perspective in the understanding and the training of the ability of elderly road users to remain accurate in their judgements.

Simulator training with a forward collision warning system: effects on driver-system interactions and driver trust.

OBJECTIVE: The study addressed the role of familiarization on a driving simulator with a forward collision warning (FCW) and investigated its impact on driver behavior. BACKGROUND: Drivers need a good understanding of how an FCW system functions to trust it and use it properly. Theoretical and empirical data suggest that exploring the capacities and limitations of the FCW during the learning period improves operating knowledge and leads to increased driver trust in the system and better driver-system interactions.The authors tested this hypothesis by comparing groups of drivers differing in FCW familiarity. METHOD: During the familiarization phase, familiarized drivers were trained on the simulator using the FCW, unfamiliarized drivers simply read an FCW manual, and control drivers had no contact with the FCW. During the test, drivers drove the simulator and had to interact with traffic; both familiarized and unfamiliarized drivers used the FCW, whereas controls did not. RESULTS: Simulator familiarization improved driver understanding of FCW operation. Driver-system interactions were more effective: Familiarized drivers had no collisions, longer time headways, and better reactions in most situations. Familiarization increased trust in the FCW but did not raise system acceptance. CONCLUSION: Familiarization on the simulator had a positive effect on driver-system interactions and on trust in the system. The limitations of the familiarization method are discussed in relation to the driving simulator methodology. APPLICATION: Practicing on a driving simulator with driving-assistance systems could facilitate their use during real driving.

Are car daytime running lights detrimental to motorcycle conspicuity?

For a long time, motorcycles were the only vehicles with daytime running lights (DRLs), but this conspicuity advantage has been questioned due to the rapidly increasing introduction of DRLs on cars as well. The present experiment was designed to assess effects of car DRLs on motorcycle perception in a situation that specifically brought attentional conspicuity to bear. Photographs representing complex urban traffic scenes were displayed briefly (250 ms) to 24 participants who had to detect vulnerable road users (motorcyclists, cyclists, pedestrians) appearing at different locations and distances. Car DRLs hampered motorcycle perception compared to conditions where car lights were not on, especially when the motorcycle was at a greater distance from the observer and when it was located in the central part of the visual scene. Car DRLs also hampered the perception of cyclists and pedestrians. Although the globally positive safety effect of car DRLs is generally acknowledged, our study suggests that more attention should be paid to motorcyclists and other vulnerable road users when introducing car DRLs. Several means of improving motorcycle conspicuity in car DRL environments are discussed.

Age-related differences in street-crossing safety before and after training of older pedestrians.

International accident statistics indicate that elderly pedestrians make up an extremely vulnerable road-user group. Past research has shown that older adults make many unsafe street-crossing decisions and adopt insufficient safety margins, especially when vehicles are approaching at high speed. Apart from studies on road design and speed-limit countermeasures, there is surprisingly no road-safety research on behavior-based measures to improve older pedestrians' safety. In this line, the present study was aimed at (i) assessing the effectiveness of a training program for older pedestrians that combined behavioral and educational interventions, and (ii) examining whether and to what extent age-related differences in street-crossing safety could be reduced after training older adults. Twenty seniors were enrolled in a training program. Before, immediately after, and six months after training, street-crossing behavior was assessed using a simulated street-crossing task. Twenty younger participants performed the same simulated task to obtain a baseline measure. The results showed that the training produced significant short- and long-term benefits, due to a shifting of the decision criteria among the older participants towards more conservative judgments. When compared with the younger group, the older participants improved their behavior considerably so that significant differences in the mean safety-related indicators were no longer observed. However, the older participants' ability to take the oncoming car's speed into account did not improve. Even after training, and contrary to younger adults, older participants were found to make more and more unsafe decisions as the car's speed increased, putting them at a higher risk at high speeds. This finding may reflect age-related perceptual and cognitive difficulties that cannot be remedied by a behavioral or educational training method. The present findings underline that high speed is an important risk factor for elderly pedestrians that should be handled by effective speed reduction measures (i.e. speed ramps, road narrowing).

The role of perceptual, cognitive, and motor abilities in street-crossing decisions of young and older pedestrians.

PURPOSE: The present experiment investigated the role of perceptual, cognitive, and motor abilities in street-crossing behaviour with ageing. Previous research has shown that older pedestrians make many unsafe crossing decisions when cars are approaching at high speeds, and miss many crossing opportunities when car speeds are low. The older subjects seem to ignore information about the speed of the approaching cars and to preferentially use simplifying heuristics based on vehicle distance. The objective of the present study was to better understand the underlying age-related changes that lead to these behaviours, with a specific focus on perceptual factors. METHOD: Twenty young (age 20-30), 21 younger-old (age 61-71), and 19 older-old (age 72-83) participants took part in the experiment. All participants individually carried out a simulated street-crossing task and took a battery of functional tests assessing perceptual, cognitive, and motor abilities. RESULTS: In line with earlier findings, the seniors made a greater number of incorrect crossing decisions, with many risky decisions when the vehicle was approaching at a high speed and many missed opportunities at a low speed. Correlation and regression analyses pointed out several functional performance measures as predictors of the way the pedestrians took or did not take information about vehicle speed into account in their decisions. Processing speed and visual attention abilities were shown to play the most important role in explaining the variance in incorrect decisions: these abilities allowed participants to focus their attention on the relevant speed information and to make timely, correct decisions. Time-to-arrival estimates, which informed the pedestrians about the time available for crossing, were found to be the second most predictive factor. Walking speed, by way of which the pedestrians adapted their crossing pace to the perceived available time, also came into play. Inhibition abilities ended up as the last functional predictor; they allowed the pedestrians to ignore irrelevant information and inhibit automatic but unsuitable responses. CONCLUSIONS: The present study provided a multidimensional explanation of increased gap-selection difficulties with ageing, including a combination of perceptual, cognitive, as well as physical performance declines with increasing age. The findings have implications for improving older pedestrians' safety in terms of speed limits, road design, and training.

Can headway reduction in fog be explained by impaired perception of relative motion?

OBJECTIVE: The goal of this study was to provide a better understanding of driver behavior in fog. BACKGROUND: Impaired perception of changes in headway is hypothesized to be one of the reasons for shorter following distances in foggy conditions as compared with clear weather. METHOD: In the experiments described here, we measured response time for discriminating between whether the vehicle ahead is getting closer or farther away. Several visibility conditions were studied, ranging from a no-fog condition to a condition in which the vehicle could be seen only by its rear fog lights. RESULTS: Fog conditions increased response times when the outline of the vehicle was barely visible or not visible at all. The longer response times in fog were attributable to the low contrast of the vehicle outline when still visible and to the smaller spacing between the two lights when the outline could not be properly perceived. Moreover, response times were found to be shorter for shorter following distances and for faster accelerations. CONCLUSION: Reducing headway could be a way for drivers to achieve faster discrimination of relative motion in foggy weather. More specifically, shortening one's following distance until visibility of the lead vehicle changes from bad to good may have a perceptual control benefit, insofar as the response time gain compensates for the reduction in headway under these conditions. APPLICATIONS: Potential applications include improving traffic safety. The results provide a possible explanation for close following in fog and point out the importance of rear-light design under these conditions.

The effects of aging on street-crossing behavior: from estimation to actual crossing.

Based on an interactive road-crossing task, this study examined age-related effects on crossing decisions and whether or not age affects behavioral adjustments to the time gap. It also compared crossing-task decisions to previously observed estimation-task decisions [Lobjois, R., Cavallo, V., 2007. Age-related differences in street-crossing decisions: the effects of vehicle speed and time constraints on gap selection in an estimation task. Accident Analysis and Prevention 39 (5), 934-943]. The results showed that older adults selected a greater mean time gap and initiated their crossing sooner than the younger ones, indicating an attempt to compensate for their increased crossing time. However, older adults accepted shorter and shorter time gaps as speed increased, putting them at a higher risk at high speeds. Regarding adaptive behavior, the analyses showed that all groups adjusted their crossing time to the available time. Comparison of crossing decisions and estimations revealed that the young group had a greater number of tight fits and missed fewer opportunities on the crossing task, whereas these differences did not appear in the elderly. This suggests that the crossing decisions of younger adults are much more finely tuned to time gaps in actual crossing tasks than in estimation tasks and that older adults have trouble calibrating perception and action and perceiving possibilities for action.

Age-related differences in street-crossing decisions: the effects of vehicle speed and time constraints on gap selection in an estimation task.

Two experiments were conducted to study how age affects street-crossing decisions in an estimation task, with particular emphasis on how oncoming vehicle speed and a time constraint influence the time gap deemed acceptable for crossing. Experiment 1 showed that when there was a time constraint, all age groups selected a shorter time gap for the higher speed. This was associated with a large number of missed opportunities for the low speed and many unsafe decisions for the high speed. In the second experiment, which had no time constraint, young pedestrians operated in a constant-time mode regardless of speed, whereas older pedestrians accepted shorter and shorter time gaps as speed increased. The results seem to indicate that the effect of speed is due to a mixed operating mode of participants, whose decisions may be based on either time or vehicle distance, depending on the task requirements and on the participant's own ability to meet those requirements.