The role of peripheral vision in vertical road sign identification and discrimination

A study on the visual recognition patterns of multi-information guide signs based on eye movement data analysis

A two-factor experiment was devised to assess the appropriateness of the quantity and arrangement of information on multi-information guide signs at unique, spacious exits on elevated expressway sections. This experiment investigated 77 signs containing varying amounts of road name information and different placements of destination road names. The research entailed an indoor experiment that incorporated eye-tracking technology and involved the analysis of a total of twenty-eight indicators. A comprehensive index system was developed, identifying three key aspects: visual recognition efficiency, visual recognition difficulty, and visual fatigue. Utilizing repeated measure analysis of variances, the impact of these two factors was examined to identify significant indicators and establish a comprehensive assessment indicator system. The Technique for Order of Preference by Similarity to Ideal Solution method, in conjunction with the coefficient of entropy weight, was employed to assess the effectiveness of these two factors. The findings demonstrated that the 28 eye-movement indicators utilized in this study effectively constitute a valuable indicator system for evaluating drivers' visual recognition characteristics. These indicators capture the subtle psychophysical traits inherent in the process of recognizing signs, including visual recognition efficiency, difficulty, and fatigue. Regarding the first experimental factor, the number of sign road names significantly influences drivers' visual recognition characteristics (Sig < 0.05). Specifically, an increase in the number of sign road names leads to diminished visual recognition efficiency and heightened visual recognition difficulty and fatigue. Consequently, it is advisable to restrict the number of sign road names to a maximum of six per sign under typical circumstances, with nine being the limit under special conditions. As for the second experimental factor, the placement of the destination road name within the sign layout exerts a significant impact on visual recognition characteristics (Sig < 0.05). Each type of multi-information sign exhibits a distinct visual recognition pattern. Generally, the upper portion of the sign is more easily recognized, while the lower part poses greater recognition challenges. Therefore, to mitigate visual recognition risks, it is recommended that road information placement be prioritized based on actual usage conditions.

Influence of in-Vehicle Audio Warning on Drivers' Eye-Movement and Behavior at Flashing Light-Controlled Grade Crossings

OBJECTIVE

This study aims to evaluate the effect of in-vehicle audio warning at flashing-light-controlled grade crossings based on driving simulation and eye-tracking systems.

BACKGROUND

Collisions at flashing-light-controlled grade crossings have severe consequences. In-vehicle audio warning has the potential to regulate driver behavior. However, whether this improvement occurs through priming drivers' visual search patterns is not yet clear.

METHOD

Drivers' visual activity and behaviors were recorded. The effect of a warning was tested with a series of flashing light trigger times (FLTTs) ranging from 2s to 6s with a 1s increment. Different driving conditions (i.e., clear and fog) and driver experience were considered in the experiment design.

RESULTS

Warnings could guide the allocation of both overt and covert attention, as well as raise drivers' situation awareness, manifesting as the enhanced perception of signs and better understanding of the flashing red light. Significant improvement in the stop-compliance rate was found in warning scenarios, particularly with a late FLTT. The decreased saccade duration and increased fixation duration on the signal implied a dilemma-zone effect when the FLTT was lower than 4s. Furthermore, reduced fixation duration on signs and signals was found in foggy conditions. Non-professional drivers had a wider search range than their counterparts.

CONCLUSION

In-vehicle audio warning is an effective countermeasure for improving crossing safety by optimizing visual search strategy.

APPLICATION

In-vehicle audio warnings warrant promotion at grade crossings based on the driver assistance system.

Duration perception in peripheral vision: Underestimation increases with greater stimuli eccentricity

Duration perception plays a fundamental role in our daily visual activities; however, it can be easily distorted, even in the retinal location. While this topic has been extensively investigated in central vision, similar exploration in peripheral vision is still at an early stage. To investigate the influence of eccentricity, a commonly used indicator for quantifying retinal location, on duration perception in peripheral vision, we conducted two psychophysical experiments. In Experiment 1, we observed that the retinal location influenced the Point of Subjective Equality (PSE) but not the Weber Fraction (WF) of stimuli appearing at eccentricities ranging from 30° to 70°. Except at 30°, the PSEs were significantly longer than 416.7 ms (25 frames), which was the duration of standard stimuli. This suggested that participants underestimated duration, and this underestimation increased with greater distance from the central fixation point on the retina. To eliminate the potential interference of the central task used in Experiment 1, we conducted a supplementary experiment (Experiment 2) that demonstrated that this central task did not change the underestimation (PSE) but did influence the sensitivity (WF) at an eccentricity of 50°. In summary, our findings revealed a compressive effect of eccentricity on duration perception in peripheral vision: as stimuli appeared more peripheral on the retina, there was an increasing underestimation of subjective duration. Reasons and survival advantages of this underestimation are discussed. Findings provide new insight on duration perception in peripheral vision, highlighting an expanding compressive underestimation effect with greater eccentricity.

Eye movement as a function to explore the effects of improved signs design and audio warning on drivers' behavior at STOP-sign-controlled grade crossings

Train-vehicle collisions at STOP-sign-controlled grade crossings attract many concerns in China and across the world. Researchers have demonstrated that the cost-effective approaches to improve grade crossing safety are the redesign of signs and pavement markings as well as the application of in-vehicle audio warning. However, the impacts of improved signs design and audio warning on drivers' visual performance have barely been discussed. This study explored the effects of improved signs design and audio warning on drivers' eye movement patterns and driving behavior at STOP-sign-controlled grade crossings, by conducting a driving simulator experiment. Three types of grade crossing scenarios: 1) the conventional signs design (Baseline), 2) improved signs design (PS), and 3) improved signs design and three-stage audio warning (PSW), were modeled in a driving simulation system and tested under a series of train TTC (no train, 4 s, 7 s, 10 s, 13 s) conditions. Foggy conditions and drivers' characteristics, i.e., gender and vocation were considered in the experiment design. Seven variables describing both drivers' fixation patterns and driving performance were collected and analyzed in this study, e.g., total fixation duration, distance to stop line at the first fixation, fixation transition probability, stop compliance, speed, maximum deceleration rate and minimum time-to-collision. Results revealed that the improved design of signs and the audio warning could prime drivers' expectation of the grade crossing in advance since drivers could drive at a lower speed, perceive signs timely, and conduct an earlier visual search for the train with these countermeasures. Besides, in PS and PSW scenarios, drivers attached more importance to the STOP sign, and they were more cautious in estimating the time-to-arrival of the train by repeatedly fixating on these two areas. The improvement in fixation performance of drivers in PS and PSW contributed to a more comfortable deceleration. Compared with no warning scenarios, higher compliance rates were observed with audio warning, especially with a short train TTC (4 s and 7 s). However, no significant difference was found between PS and Baseline, indicating the limited safety benefits of improved signs design. Minimum time-to-collision for those drivers who ignored the warning did not increase significantly in both PS and PSW. Additionally, heavy fog limited drivers' perception of signs and led to a later and shorter fixation. For gender effect, males had a lower fixation duration on the STOP sign and lower compliance rate than females. Moreover, female drivers could perceive the approaching train earlier than males, especially in PS and PSW. These findings suggested that the improved signs design and in-vehicle audio warning improved drivers' visual and behavioral performance and had the potential to enhance safety at STOP-sign-controlled grade crossings.

Unequal allocation of overt and covert attention in Multiple Object Tracking

In many real-life contexts, where objects are moving around, we are often required to allocate our attention unequally between targets or regions of different importance. However, typical multiple object tracking (MOT) tasks, primarily investigate equal attention allocation as the likelihood of each target being probed is the same. In two experiments, we investigated whether participants can allocate attention unequally across regions of the visual field, using a MOT task where two regions were probed with either a high and low or with equal priority. Experiment 1 showed that for high-priority regions, accuracy (for direction of heading judgments) improved, and participants had more frequent and longer fixations in that region compared with a low-priority region. Experiment 2 showed that eye movements were functional in that they slightly improved accuracy when participants could freely move their eyes compared with when they had to centrally fixate. Replicating Experiment 1, we found better tracking performance for high compared with low-priority regions, in both the free and fixed viewing conditions, but the benefit was greater for the free viewing condition. Although unequal attention allocation is possible without eye movements, eye movements seem to improve tracking ability, presumably by allowing participants to fixate more in the high-priority region and get a better, foveal view of the objects. These findings can help us better understand how observers in real-life settings (e.g., CCTV monitoring, driving) can use their limited attentional capacity to allocate their attention unequally in a demand-based manner across different tracking regions.

Urban Mid-Block Bicycle Crossings: The Effects of Red Colored Pavement and Portal Overhead Bicycle Crossing Sign

This paper aims to investigate the effectiveness of some mid-block bicycle crossing elements by analyzing the drivers’ behavior, when approaching the bicycle crossings in a real road experiments with 18 participants. The eye-tracking instrument has been used to monitor the driver’s visual behavior during the test in an instrumented vehicle with GPS (global positioning system) and an inertial measurement unit (IMU). In particular, the drivers’ gaze was investigated frame by frame while approaching the mid-block bicycle crossings. The results showed that the red colored pavement increased the visibility of the mid-block crossing zone to 65.3% with respect to zebra crossing 59.6%. The drivers’ visual field was also narrowed by the portal overhead bicycle crossing sign and, consequently, drivers reduced their velocity and looked more to the vertical signs by 28%. The drivers’ speed reduction helped drivers to see the mid-block crossing elements from a greater distance with a higher fixation duration.

Passive anti-sunlight glare traffic signs with non-axisymmetric freeform lens design

This paper proposes a passive optical brightening element design, a non-axisymmetric freeform lens (NAFL), arranged and assembled on a traditional traffic sign. NAFL is the first optical design which can effectively solve the traffic problem that direct sunlight affects the driver's inability to look directly at the traffic sign. The NAFL can converge the sunlight behind the traffic sign and diverge forward to 150 meters away. In this way, the NAFL array combinations on the traffic sign can directly rely on sunlight as image information pixels. According to the simulation, the optical efficiency of the NAFL can be as high as 81.5%. Besides, the angular tolerance is also analyzed to evaluate the working hours of the NAFL. Finally, we made the prototype and proved that such passive brightening components could effectively improve the traffic sign's visibility in harsh sunlight.

Effects of taillight shape on conspicuity of vehicles at night

Taillight shape in a vehicle provides an essential lighting signal that enables the vehicle to be seen from the rear at night, thereby preventing rear-end crashes. This study aims to investigate the effects of taillight shape on vehicle conspicuity, and proposes ergonomic taillight shape solutions to vehicle designers and manufacturers. Two complementary experiments were conducted to examine three types of taillight shapes at three design levels. The first experiment was designed to investigate the detection speed of a driver and the fixation duration and fixation counts on leading vehicles with different taillight shapes, based on an eye-tracking methodology. The second experiment was designed to investigate the dynamic visual searching performance of a trailing driver for leading vehicles with different taillight shapes, based on a visual search task. The experimental results indicated that a long line-shaped taillight (striplight) was the optimal ergonomic solution for enhancing vehicle conspicuity. Vehicles with an enclosed contour-shaped taillight were more salient than those with an open contour-shaped taillight. Moreover, the experience and gender of the driver and the vehicle-observer distance were found to be closely related to vehicle conspicuity, and therefore, must be considered by vehicle designers when applying a specific taillight shape design. This study provides insights into the taillight shape design that not only aid vehicle designers or manufacturers in enhancing vehicle safety but also enable potential vehicle buyers to choose a safe lighting system.

Flashing in-curb LEDs and beacons at unsignalized crosswalks and driver's visual attention to pedestrians during nighttime

Driver's visual attention (eye movements) and driving behaviour (kinematic data) were assessed when approaching an experimental crosswalk that included flashing white in-curb LED strips, flashing orange beacons, backlit 'Yield here to pedestrians' vertical signs, and enhanced lighting when a staged pedestrian attempted to cross. An experimental condition in which all devices were active was compared with a control condition in which only enhanced lighting and backlit vertical signs were active. The results showed a significant increase of motorists' yielding compliance, distance of first fixation to the pedestrian area, standard deviation for horizontal eye movements in the experimental condition. The introduction of flashing in-curb LED strips and flashing orange beacons proved to be very effective in increasing the night-time safety of the pedestrian crossing. Practitioner summary: The study investigated the effects of flashing in-curb LED strips and beacons on driver's visual attention (eye movements) and speed when approaching a crosswalk during night-time. The results showed that the combination of these flashing devices significantly increased yielding compliance and the distance of pedestrian detection. Abbreviations: ANOVA: analysis of variance; EU: European Union; HAWK: high intensity activated crosswalk system; LED: light-emitting diode; PHB: pedestrian hybrid beacons; ROI: region of interest; RRFB: rectangular rapid flashing beacons; UK: United Kingdom; US: United States.

Driver's visual attention to different categories of roadside advertising signs

Roadside advertising signs are a salient potential source of driver's distraction. Previous research has mainly investigated driver's visual attention to billboards, which represents only one category of advertising signs. In this study, driver's visual attention was assessed in a naturalistic driving setting for six categories of roadside advertising signs: vendor signs, billboards, movable display boards, single and multiple commercial directional signs, and gas price LED displays. Fixation rate, fixation duration, fixation distance and driving speed were assessed in a sample of 15 drivers along a 30-km route including a total of 154 advertising signs belonging to the six categories described above. The role of clearance from the road, elevation, height, width, surface, number and size of characters, total number of characters, side of the road (driving side, opposite side), context (rural, urban), were also considered. Overall 24% of the roadside advertising signs were fixated. Fixation rate was significantly influenced by sign category, clearance from the road and number of characters. Median value for fixation duration was 297 ms. Fixation duration was significantly influenced by speed, elevation from road level, number of medium size characters, and was higher in the rural context. Median value for fixation distance was 58.10 m, and was significantly influenced by advertising sign category, character count and speed.