Road User Understanding of Bicycle Signal Faces on Traffic Signals (2020) / Chapter Skim
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2. Background and Literature Review
2. Background and Literature Review
Pages 7-25
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states that "The proper use of traffic control devices should provide the reasonable and prudent road user with the information necessary to efficiently and lawfully use the streets, highways, pedestrian facilities and bikeways." This report places particular emphasis on the bicyclist as the road user of concern operating on streets and bikeways that cross through signalized intersections. The following subsections provide content on the visibility, comprehension, compliance and human error, and evaluation methods for traffic control devices focused on traffic signals.
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To ensure that the traffic signals are visible to the road user, designers should consider the size, design, and placement of the device. A road user's cone of vision can be defined as excellent from three to five degrees.
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. Comprehension of traffic signals by road users is a critical factor in compliance and, ultimately, in the device operating correctly.
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. Compliance and Human Error Once the road user recognizes the traffic signals and understands their meaning, the user is required to comply with the directive information in a timely manner.
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. Evaluation Methods for Traffic Control Devices Methodological approaches to TCD evaluation can take many forms, including surveys, laboratory testing, driving simulators, test tracks, and in-field observations (Figure 4)
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Figure 4. Types of Human Factors Evaluation for Traffic Control Devices Visibility and Comprehension of Bicycle Signal Face No published research studies were found that have directly addressed the visibility of the bicycle signal face.
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Examples of International Bicycle Signal Faces 13
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One conflict between motor vehicles and trail users was observed in 59 hours, therefore leading the study to conclude that the bicycle traffic signal did not lead to driver confusion. During the postremoval phase, bicyclists were observed to be more likely to enter the intersection during a noncompliant phase and the capacity of the traffic signal to accommodate the compliant bicyclists was reduced.
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Blog and News Posts While blog and news posts are not peer-reviewed research, they do provide some anecdotal observations of potential issues. Recent installations of bicycle traffic signals in Seattle, WA, Brooklyn, NY, and Chicago, IL have drawn blog posts and news stories about driver confusion with bicycle signal displays.
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. Compliance There is more literature on cyclist compliance at signalized intersections, though most of the studies document compliance at general traffic signals.
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Two types of cyclist compliance were evaluated, those that moved straight through the intersection violating the red signal or those that made an illegal right turn. Overall, there was high compliance and no difference between behaviors at bicycle signals and general traffic signals, suggesting good comprehension of the bicycle symbol in the signal face.
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Observed Cyclist Compliance with Traffic Signals Greenshields et al. studied the impact of "Cycle Gates" used in the United Kingdom, which included the provision of separate stop line and bicycle signals for cyclists and a separate stop line for vehicles to prevent left-hook collisions (Greenshields et al., 2018)
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. Their findings revealed that direction of travel, presence of other road users, gender, age, helmet use, previous crash experience, detection reliability and presence of pedestrian crossings all had an effect on cyclist compliance.
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In a fully split-phase treatment, the through bicyclists and turning vehicles are separated in time with bicycle signals. The study did not document any driver confusion with bicycle traffic signals.
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The experiments in the driving simulator usually involved subjects driving in a grid and being presented with various signal display alternatives and their actions were recorded. The results of these studies demonstrated that simultaneous displays (green arrow and green ball, green arrow and red ball)
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. These studies used surveys to understand driver comprehension of the traffic control devices with and without supplemental signs.
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The report also stated the primary signal be located on the near side of the intersection and they should be separated vertically and/or horizontally by at least 8 feet from the nearest traffic signal head or the pedestrian signal head for the same approach (Korve et al.
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Road users first need to see the traffic control device, correctly comprehend its meaning and respond accordingly. A review of bicycle-focused literature showed no published research studies that directly addressed visibility and comprehension of the bicycle signal face or the transferability of design 24
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Review of literature pertaining to traffic control devices for vehicles revealed the importance of visibility and conspicuity of traffic signals in reducing collisions. Studies also revealed extensive testing of various signal display alternatives to determine optimal displays and signal head configurations to communicate protected/permissive movements.
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