Road User Understanding of Bicycle Signal Faces on Traffic Signals (2020)

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CHAPTER 5 Identified Research Gaps Three gaps in the knowledge were identified following the literature review, inventory of existing bicycle symbol signal faces, and interviews with stakeholders. In priority order, these research gaps are specific to a road user’s understanding of bicycle symbols in the signal are: • Optimal methods to communicate allowable, protected, or permissive movements to bicyclists at signalized intersections. • Evaluation of size, placement, and orientation of bicycle signal faces on bicyclist and driver comprehension and compliance. • Guidance on visibility and detection of bicycle symbols in signal faces by lens size and distance. The following subsections briefly describe the research gaps and associated contexts. Full research needs statements, in the NCHRP format, were developed and are included in Appendix C. It should be noted that there are aspects of the research gaps that somewhat overlap; however, they are formulated as distinct research statements. It would be possible to combine elements of each statement into a larger research project. Optimal Methods to Communicate Allowable, Protected, or Permissive Movements to Bicyclists at Signalized Intersections The Interim Approval for the use of bicycle signals faces (IA-16) in the U.S. limits their use where the bicycle movement is “protected from any simultaneous motor vehicle movement at signalized intersections (FHWA, 2014).” This requirement suggests that the GREEN BICYCLE display indicates to a person on a bicycle that their movement is protected. Compliance with this provision requires the installation of fully protected phases for bicyclists, and often requires exclusive turn lanes for left and right turns for motor vehicle movements that cross the bicycle lane or signal timing strategies which limit the available green time for bicyclists to proceed while all adjacent vehicle traffic is stopped. IA-16 also prohibits the use of signs alone to restrict bicycle movements. If it is necessary, turn arrows on the bicycle signal face can be used to communicate allowable movements and to restrict conflicting bicycle movements. No published research was found on the best ways to communicate with a person on a bicycle or other road users which movements are allowable from the bicycle lane and whether those movements are protected or permissive. A number of agencies are experimenting, through the MUTCD experimental process, with allowing permissive motor vehicle turns across the bicycle facility when bicyclists have displayed the GREEN BICYCLE symbol. Other agencies are using a FLASHING YELLOW BICYCLE to indicate a permissive bicycle movement. In some jurisdictions, the GREEN BICYCLE symbol varies from protected to permissive depending on installation date as discussed in the agency in interviews for this research. In the stakeholder interviews, the need for this research was often discussed and ranked highest in need. 68 

Further research is needed to identify or confirm the best method to communicate with a person on a bicycle and other road users through traffic control devices. The primary research objective would be to develop an understanding of actual bicyclist movements while facing the GREEN BICYCLE symbol from typical intersection configurations, including what movements are allowable from the bicycle lane. This could be completed through observational methods. A human factors experiment would be designed and executed in a controlled lab or field research study to quantify comprehension of the existing GREEN BICYCLE symbol, comprehension of alternative traffic control devices such as four section heads with the green ball for permissive phases, flashing signals, signs, or pavement markings. In addition, while the use of arrow displays to control bicycle movements is likely intuitive, there has not been any human factors research to verify this understanding or explore alternatives. As part of this research, some consideration would be given to the comprehension of people driving and using electric mobility devices (e.g., scooters, hoverboards, etc.). Evaluation of Size, Placement, and Orientation of Bicycle Signal Faces on Bicyclist and Driver Comprehension and Compliance Interim Approval of bicycle signals faces (IA-16) provides guidance on the design and placement of bicycle signals at intersections and relative to other vehicular traffic signal indications. NACTO’s Urban Bikeway Design Guide and the MassDOT Separated Bike Lane Planning and Design Guide provide additional guidance. Cities, however, have implemented a wide variety of bicycle signal designs and there is limited information on how the design and placement positively or negatively affect bicycle operations and safety. For example, there is no consensus on the horizontal and vertical distance from vehicular traffic signals or the use of near- side signal heads. Of the approximately 500 bicycle signal installations surveyed in the U.S. as part of this project, a majority (51%) use two or more bicycle signal heads per approach but there is no standard requiring more than one signal head. Locations that had two or more bicycle signal heads per approach typically used a far-side/near-side arrangement. With more bicyclists and bicycle traffic signals, there is greater variability in how these traffic control devices are designed and implemented. Ultimately, this impacts how they command respect from roadway users. There is limited research on how a bicyclist’s behavior is affected by the size, placement, and orientation of bicycle traffic signals. Current bicycle signal designs mirror vehicular signals in many ways, which may cause confusion and raises questions about the transferability of these design assumptions. For example, motor vehicle traffic signal indications are placed within a driver’s cone of vision as they approach an intersection. Does the bicyclist cone of vision differ from a driver’s cone of vision? Is there a benefit to overall operations of allowing the motor vehicle driver to see the bicycle signal face? Finally, the interview with agency practitioners revealed questions about whether bicycle signal design affects user comprehension and, ultimately, traffic signal compliance. In all, there is limited information on which bicycle signal design best meets MUTCD traffic control device principles and which strategies support uniformity principles for all users under different bikeway design configurations. The primary research objective would be to determine optimal design and placement of bicycle signals and how compliance with bicycle signal relates to comprehension. The research would consider the influence of the number of bicycle signal heads per approach; near- and far-side installations; size of indication (4-, 8-, or 12-inch); horizontal and vertical distance of bicycle signals to vehicle signals; presence of louvers and backplates; and the distance from bicycle stop line to bicycle signal. Potential research methods could include a) video data collection, b) 69 

intercept and group survey, and c) naturalistic eye-tracking study, d) simulator tests, and e) closed- course test tracks. Guidance on Visibility and Detection of Bicycle Symbols in Signal Faces by Lens Size and Distance Conspicuity and the distance at which the bicycle symbol in the signal face is distinguishable is key to the safety of bicyclists and other road users. IA-16 currently requires far-side bicycle signals to use 8- or 12-inch lenses, while near-side lenses can be 4-, 8-, or 12-inch. No published research studies were found that have directly addressed the visibility of the bicycle symbol in the signal lens. Visibility includes placement for optimal detection by road users, conspicuity of the lens, and detection distances. There are two separate issues related to the comprehension of the bicycle symbol in the signal face: 1) recognizing that the symbol face denotes the signal as exclusive for bicycles, and 2) knowing which movements are allowed by the displayed indications. No published research studies were found that have directly addressed comprehension of the bicycle symbol in the signal face, either for bicyclists or drivers. The guidance for signal face sizing (lens size) by distance appears to be derived primarily from the guidance for motor vehicle signals. In the agency interviews, lack of clear guidance was often cited as a need. No human factors research on the size of the signal lens or the design of the bicycle symbol within the lens, and longitudinal placement of the signal head to optimize the detection distance from the stop line for cyclists were identified in the literature. In addition to the detection distance of the bicycle symbol in the signal face, the design of the bicycle symbol within the lens face itself plays a significant role in both motorist and bicyclist comprehension. While there are slight variations in the symbol presented internationally, little research or guidance has been provided on the optimal design of the signal face. Because the bicycle symbol plays a significant role in distinguishing between separate user controls at an intersection, refining the design of existing symbols could improve the conspicuity of the signal. Finally, a source of potential driver confusion is that the color of the bicycle signal indications is the same as vehicular signal indications and at some distances and LED intensities, the bicycle symbol may not be distinguishable from a circular display, causing additional confusion. A similar issue was identified in the first light-rail transit signals, which led to the adoption of a monochromatic and unique symbol (Korve, 1996). The primary objective of the research would be to develop guidelines for the overall bicycle symbol design in the signal face, including size and brightness to improve conspicuity, improved design of bicycle symbol in the signal face for optimal detection, and determination of bicycle signal face detection distance. The research would explore lens size for various applications of far- side and near-side placement. The research would include a survey of design practice to identify approaches that are used in the U.S. and internationally. Following the review, research would conduct a controlled lab or field study to determine optimal lens size, bicycle symbol design, and detection distances based on the data analysis. Consideration should be given to methods that address potential driver confusion with bicycle symbols and green ball at certain distances. 70