Traffic Gap Detection for Pedestrians with Low Vision

Abstract

Purpose Pedestrians with low vision have identified crossing the street as a difficult task. With the increasing complexity of the crossing environment (actuated signals, roundabouts), the challenges are increasing. The purpose of this study was to evaluate the effect of two types of vision loss (central or peripheral) on the ability to detect gaps in traffic. Methods 41 subjects participated with 14 being fully sighted, 10 having central vision loss from age-related macular degeneration (AMD), and 17 having peripheral vision loss from either retinitis pigmentosa (RP) or glaucoma (GL). Standing at entry and exit lanes of a roundabout, subjects depressed a hand held trigger to indicate when there was a sufficient gap in traffic to cross the street. A total of 12 two minute intervals were completed including four of those intervals with occluded hearing. Results No difference was found in the ability of the three subject groups to identify crossable or short gaps. There were significant differences in latency and safety margin. The AMD subjects did not perform as well as the fully sighted or the subjects with RP/GL. When hearing was occluded the two vision loss groups did not show a change in sensitivity but the fully sighted group did, being more sensitive when hearing was occluded. Conclusions The purpose of this study was to evaluate the effect of low vision on the ability to detect crossable gaps in traffic. The findings suggest that subjects with AMD have an increased risk because they show significant latency in their identification of gaps and this in turn results in a reduction of safety margin.

Are Normally Sighted, Visually Impaired, and Blind Pedestrians Accurate and Reliable at Making Street Crossing Decisions?

“…This conclusion also is supported by the results of Geruschat et al, who found that subjects with VA loss from age-related macular degeneration (AMD) performed similarly to normally sighted subjects in correctly identifying crossable and short gaps. 19 It also appears that the minimum VF size required to make accurate and reliable street crossing decisions lies between a 5.48 and 52.278 radius -the radii of the VF extents of the visually impaired subjects in the study of Cheong et al 4 and our studies, respectively. Further research is required to determine systematically how small the VF extent can be before a person no longer is able to detect crossable vehicular gaps accurately and reliably.…”

“…This result confirms the finding of Geruschat et al, who also found no significant difference in visually impaired subjects' traffic gap detection performance between the conditions of VþH and when hearing was occluded. 19 The nonlinear function describing the relationship between the street crossing decision variable and the vehicular gap time suggests that the decision variable is not discriminable across gap times below and above a certain value (gap time). All gap times below a certain value, quantified in our study as t min , will be classified by the subject as being ''insufficient time to cross.''…”

Street-Crossing Decision-Making: A Comparison between Patients with Age-Related Macular Degeneration and Normal Vision

“…However, the results of Geruschat et al 5 may be biased whereby the ability of the AMD subjects to identify accurately crossable and uncrossable gaps is inflated. This is because in their study there was an over-representation of short, uncrossable vehicular gap times assessed.…”

“…1 A key factor involved with making safe street-crossing decisions is vision. Previous street-crossing studies have shown that visually impaired and blind pedestrians, in comparison with normally-sighted pedestrians, make significantly more unsafe street-crossing decisions, 2,3 identify significantly fewer crossable gaps, [2][3][4] take significantly longer to identify a crossable gap, 2,[4][5][6] and have significantly reduced safety margins. 5 Collectively, the results of these earlier studies demonstrate that pedestrians with vision loss are potentially at risk when crossing the street in part because of their vision loss.…”

“…5 Geruschat et al measured the ability of ten subjects with AMD, 14 normally-sighted subjects, and 17 subjects with peripheral VF loss, either from retinitis pigmentosa (RP) or glaucoma, to detect crossable and short gaps in vehicular traffic at an entry and exit lane of a two-lane urban roundabout. 5 They found no significant difference between the AMD and age-matched, normally-sighted subjects in their ability to detect correctly crossable vehicular gaps, reject correctly uncrossable vehicular gaps, and detect the number of missed crossing opportunities (i.e., rejecting a vehicular gap time when it was long enough for a crossing). Therefore, these results suggest that despite their vision loss, subjects with AMD are still able to identify accurately crossable and uncrossable vehicular gaps in traffic.…”