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.

A vibrotactile wristband to help older pedestrians make safer street-crossing decisions.

INTRODUCTION: Older pedestrians are overrepresented in fatal accidents. Studies consistently show gap-acceptance difficulties, especially in complex traffic situations such as two-way streets and when vehicles approached rapidly. In this context, the present research was aimed at assessing the effectiveness of a vibrotactile device and study older pedestrian's behavior when wearing the wristband designed to help them make safer street-crossing decisions. METHOD: Twenty younger-old participants (age 60-69), 20 older-old participants (age 70-80) and 17 younger adults (age 20-45) carried out a street-crossing task in a simulated two-way traffic environment with and without a vibrotactile wristband delivering warning messages. RESULTS: The percentage of decisions that led to collisions with approaching cars decreased significantly when participants wore the wristband. Benefits tended to be greater particularly among very old women, with fewer collisions in the far lane and when vehicles approached rapidly when they wore the wristband. But collisions did not fall to zero, and responses that were in accordance with the wristband advice went up to only 51.6% on average, for all participants. The wristband was nevertheless considered useful and easy to use by all participants. Moreover, behavioral intentions to buy and use such a device in the future were greater in both groups of older participants, but not among the younger adults. PRACTICAL APPLICATIONS: This haptic device was able to partly compensate for some age-related gap-acceptance difficulties and reduce street-crossing risks for all users. These findings could be fruitfully applied to the design of devices allowing communication between vehicles, infrastructures, and pedestrians.

Mechanisms underlying cognitive conspicuity in the detection of cyclists by car drivers.

OBJECTIVE: The aim of this study was to evaluate the visibility of cyclists for motorists in a simulated car driving task. BACKGROUND: In several cases involving collisions between cars and cyclists, car drivers failed to detect the latter in time to avoid collision because of their low conspicuity. METHOD: 2 groups of motorists (29.2 years old), including 12 cyclist-motorists and 13 non-cyclist-motorists, performed a vulnerable road user detection task in a car-driving simulator. They had to detect cyclists and pedestrians in an urban setting and evaluate the realism of the cyclists, the traffic, the city, the infrastructure, the car driven and the situations. Cyclists appeared in critical situations derived from previous accounts given by injured cyclists and from cyclists' observations in real-life situations. Cyclist's levels of visibility for car drivers were either high or low in these situations according to the cyclists. RESULTS: Realism scores were similar and high in both groups. Cyclist-motorists had fewer collisions with cyclists and detected cyclists at a greater distance in all situations, irrespective of cyclist visibility. Several mechanisms underlying the cognitive conspicuity of cyclists for car drivers were considered. CONCLUSION: The attentional selection of a cyclist in the road environment during car driving depends on top-down processing. APPLICATION: We consider the practical implications of these results for the safety of vulnerable road users and future directions of research.

Training the elderly in pedestrian safety: Transfer effect between two virtual reality simulation devices.

OBJECTIVES: A virtual-reality training program has been developed to help older pedestrians make safer street-crossing decisions in two-way traffic situations. The aim was to develop a small-scale affordable and transportable simulation device that allowed transferring effects to a full-scale device involving actual walking. METHODS: 20 younger adults and 40 older participants first participated in a pre-test phase to assess their street crossings using both full-scale and small-scale simulation devices. Then, a trained older group (20 participants) completed two 1.5-h training sessions with the small-scale device, whereas an older control group received no training (19 participants). Thereafter, the 39 older trained and untrained participants took part in a 1.5-h post-test phase again with both devices. RESULTS: Pre-test phase results suggested significant differences between both devices in the group of older participants only. Unlike younger participants, older participants accepted more often to cross and had more collisions on the small-scale simulation device than on the full-scale one. Post-test phase results showed that training older participants on the small-scale device allowed a significant global decrease in the percentage of accepted crossings and collisions on both simulation devices. But specific improvements regarding the way participants took into account the speed of approaching cars and vehicles in the far lane were notable only on the full-scale simulation device. DISCUSSION: The findings suggest that the small-scale simulation device triggers a greater number of unsafe decisions compared to a full-scale one that allows actual crossings. But findings reveal that such a small-scale simulation device could be a good means to improve the safety of street-crossing decisions and behaviors among older pedestrians, suggesting a transfer of learning effect between the two simulation devices, from training people with a miniature device to measuring their specific progress with a full-scale one.

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.

Towards an explanation of age-related difficulties in crossing a two-way street.

Crossing a two-way street is a complex task that involves visual, cognitive and motor abilities, all of which are known to decline with ageing. In particular, older pedestrians may experience difficulties when crossing two-way streets because of incorrect gap acceptance choices and impossible or unperceived evasive actions. To understand the overrepresentation of older pedestrians in crash statistics, several experimental studies have sought to identify traffic-related factors as well as those related to the abilities of the individuals themselves. However, none of these studies has required participants to actually walk across an experimental two-way street with curbs, which is a particularly challenging situation for older pedestrians. To fill this research gap, a quasi-experiment was conducted in a simulator including a total of 58 healthy aged participants (25 younger-old [age 60-72] and 33 older-old [age 72-92]) and 25 young adults (aged 18-25 years). Participants carried out a street-crossing task in a simulated two-way traffic environment; curbs were present on both sides of the experimental street. Participants also undertook a battery of tests to assess their visual and cognitive abilities. In addition, during the experiment, the participants' gait parameters were recorded. In line with earlier findings, the older-old group of participants made a higher number of decisions that led to collisions with approaching cars compared with the other groups. The two groups of older participants experienced specific difficulties when vehicles were in the far lane or when they approached rapidly. A regression analysis identified visual acuity, speed of processing (assessed using the UFOV(®) test), and step length as significant predictors of collisions. Our results have implications for understanding the difficulties experienced by older pedestrians and allow to draw up several recommendations for improving their safety.

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.

Low conspicuity of motorcycles for car drivers: dominant role of bottom-up control of visual attention or deficit of top-down control?

OBJECTIVE: The aim of this study was to evaluate whether the low visibility of motorcycles is the result of their low cognitive conspicuity and/or their low sensory conspicuity for car drivers. BACKGROUND: In several cases of collision between a car and a motorcycle, the car driver failed to detect the motorcyclist in time to avoid the collision. METHOD: To test the low cognitive conspicuity hypothesis, 42 car drivers (32.02 years old) including 21 motorcyclist motorists and 21 non-motorcyclist motorists carried out a motorcycle detection task in a car-driving simulator.To test the low sensory conspicuity hypothesis, the authors studied the effect of the color contrast between motorcycles and the road surface on the ability of car drivers to detect motorcycles when they appear from different parts of the road. RESULTS: A high level of color contrast enhanced the visibility of motorcycles when they appeared in front of the participants. Moreover, when motorcyclists appeared from behind the participants,the motorcyclist motorists detected oncoming motorcycles at a greater distance than did the non-motorcyclist motorists. Motorcyclist motorists carry out more saccades and rapidly capture information (on their rearview mirrors and on the road in front of them). CONCLUSION: The results related to the sensory conspicuity and cognitive conspicuity of motorcycles for car drivers are discussed from the viewpoint of visual attention theories. APPLICATION: The practical implications of these results and future lines of research related to training methods for car drivers are considered.

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).

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.