J Uttley

Using eye-tracking to identify pedestrians’ critical visual tasks, Part 1. Dual task approach

This paper investigates the critical visual tasks of pedestrians, the first step in a review of design guidance for lighting in residential roads. Eye tracking was used to record pedestrians’ visual fixations when walking outdoors in daytime and after dark with a concurrent dual task to better understand which fixations were critical. Fixations at critical instances, these being shown by slow reactions to the secondary task, were categorised into one of eight groups. Of these, the path and other people were the most frequent items, with people more likely to be fixated at a far distance and the path at a near distance. After dark the path was more likely to be fixated and other people less likely to be fixated compared with daylight.

Using eye-tracking to identify pedestrians' critical visual tasks. Part 2. Fixation on pedestrians

This article investigates different approaches to the interpretation of eye-tracking video records of pedestrians walking outdoors to determine the apparent importance of fixation on other pedestrians and how this is influenced by the frequency of occurrence. The three approaches were as follows: the proportion of time that fixations were on pedestrians (14%), a common approach to interpretation; the proportion of fixations at critical moments that were on pedestrians (23%), critical moments being defined by a delayed response to a dual task; and the probability of an approaching pedestrian being fixated at least once (86%). These data were compared against the number of pedestrians encountered during the trials; the proportion of all fixations and the probability of fixating people were affected by the number of people encountered – only the critical-fixations data did not exhibit a trend.

Observing other pedestrians: Investigating the typical distance and duration of fixation

After dark, road lighting should enhance the visual component of pedestrians’ interpersonal judgements such as evaluating the intent of others. Investigation of lighting effects requires better understanding of the nature of this task as expressed by the typical distance at which the judgement is made (and hence visual size) and the duration of observation, which in past studies have been arbitrary. Better understanding will help with interpretation of the significance of lighting characteristics such as illuminance and light spectrum. Conclusions of comfort distance in past studies are not consistent and hence this article presents new data determined using eye-tracking. We propose that further work on interpersonal judgements should examine the effects of lighting at a distance of 15 m with an observation duration of 500 ms.

Effect of illuminance and spectrum on peripheral obstacle detection by pedestrians

Obstacle detection is an important visual task for pedestrians. An experiment was carried out to measure the ability to detect peripheral obstacles under variations of illuminance and scotopic/photopic luminance ratio and with older and younger test participants. The LED array used in this work enabled scotopic/photopic ratio to be varied whilst chromaticity was held constant. The tests employed a full-scale model with dynamic fixation and walking to better simulate pedestrian experience than in past work. Detection performance increased with illuminance, reaching a plateau at 2.0 lux. A higher scotopic/photopic ratio improved obstacle detection but only at the lowest illuminance used in this study (0.2 lux). Older participants showed poorer obstacle detection performance than younger participants but again only at the lowest illuminance.

Satisfaction and illuminances set with user-controlled lighting

This study was carried out to explore satisfaction with light levels when these are set with user-control over light level. Two ranges of illuminance were used, having maximum illuminances of 500 and 700 lux. Previous work has demonstrated that the lower range would lead to lower settings of preferred illuminance: this work was carried out to compare ratings of satisfaction with light levels set using different ranges. Results of the illuminance adjustment task demonstrated that the lower range lead to significantly lower illuminances. Results of the ratings of satisfaction with light level did not suggest a difference in satisfaction with the low and high ranges despite the significant difference in illuminances. These results suggest that occupants would set a lower light level when presented with a lower illuminance range and that they would be equally satisfied with this lower light level than if they had set a higher illuminance under a high illuminance range. This suggests the potential to reduce energy consumption without reducing satisfaction.

Maintaining foveal fixation during a peripheral detection task

Using road lighting to improve the detection of potential hazards may contribute to reduced accident rates for pedestrians, drivers and other road users. In past studies carried out to measure peripheral detection, the test participant was instructed to maintain fixation on a target during presentation of the peripheral target, but these studies did not question the degree to which this fixation was maintained. We therefore used eye tracking to record fixations during a peripheral detection task and introduced a fixation task designed to encourage fixation. It was found that observers were good at maintaining foveal fixation and there was little benefit in introducing a fixation task although this might be of greater benefit if the peripheral field contains more interesting distractions.

Illuminance required to detect a pavement obstacle of critical size

This paper investigates the illuminance needed to detect trip hazards for pedestrians walking after dark. In previous work, it was assumed that the critical obstacle height is 25 mm: further review of accident data and foot clearance data suggests instead that 10 mm is the critical height. Eye tracking records suggest a tendency for obstacles to be detected approximately 3.4 m ahead. Interpretation of obstacle detection data suggests horizontal photopic illuminances of up to 0.9 lux are required for peripheral detection of a 10 mm obstacle 3.4 m ahead, according to the scotopic/photopic ratio of the lighting and the age of the observer.

A pilot study of road lighting, cycle lighting and obstacle detection:

This paper investigates cyclists’ detection of an obstacle on the surface of the road ahead, observed in peripheral vision, and how this is affected by variations in light level from road and cycle lighting. The data analysed were the height at which a rising obstacle was detected, this simulating an approaching irregularity in the road surface. The results suggest that when cycling on a lit road, cycle lighting frequently offers no benefit for peripheral detection and may make it worse. It was demonstrated that position matters: At low illuminances, a hub-mounted lamp improved detection over a handlebar-mounted lamp. This benefit was sufficient to offset the reduction in detection found when decreasing road lighting from 2.0 lux to 0.2 lux.

The effect of ambient light condition on road traffic collisions involving pedestrians on pedestrian crossings

Previous research suggests darkness increases the risk of a collision involving a pedestrian and the severity of any injury suffered. Pedestrian crossings are intended to make it safer to cross the road, but it is not clear whether they are effective at doing this after-dark, compared with during daylight. Biannual clock changes resulting from transitions to and from daylight saving time were used to compare RTCs in the UK during daylight and darkness but at the same time of day, thus controlling for potential influences on RTC numbers not related to the ambient light condition. Odds ratios and regression discontinuity analysis suggested there was a significantly greater risk of a pedestrian RTC at a crossing after-dark than during daylight. Results also suggested the risk of an RTC after-dark was greater at a pedestrian crossing than at a location at least 50m away from a crossing. Whilst these results show the increased danger to pedestrians using a designated crossing after-dark, this increased risk is not due to a lack of lighting at these locations as 98% of RTCs at pedestrian crossings after-dark were lit by road lighting. This raises questions about the adequacy and effectiveness of the lighting used at pedestrian crossings.

Exploring the nature of visual fixations on other pedestrians

How we look at other people may affect conclusions drawn about the effect of changes in lighting when this task needs to be done after dark. This paper reports further analysis of the distance and duration of fixation on other pedestrians, updating a previous review by considering a greater number of fixations and by examining the influence on these of other characteristics such as the relative direction of travel. This analysis provides further support for a tendency to fixate others at a distance of 15 m and for a duration of 500 ms.