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CHAPTER 1 Introduction The complexity of signalized intersections, especially in busy urban settings, requires that traffic engineers and designers think carefully about the interactions of all modes and users. Geometric and operational conditions sometimes dictate that movements of the various users be separated in time for safety or other reasons. From a human factors perspective, road users must first identify the various signal displays in their visual field, then discriminate which displays apply to them and their movement. Human factors issues of visual acuity, contrast sensitivity, color perception, and expectations contribute to the userâs ability to understand the display (Wickens et al., 1998). Pedestrians, among the most vulnerable of users, have separate displays and timing practices. The displays, consisting of a stencil of a person walking displayed in white and solid or flashing orange with an optional numerical countdown display, is distinct from the circular and arrow red-yellow- green displays used for motor vehicles. Though evidence suggests drivers may use the countdown display for cues about the upcoming clearance time (Kitali et al., 2018), road user confusion with pedestrian signals is not an identified issue. Similarly, light rail transit (LRT) vehicles, when traveling in the right-of-way, are controlled by distinct signals using white bars and triangles. While some early designs featured red and green displays viewable by drivers, which caused confusion (Korve et al., 1996), the current displays are not a concern. Bicycle signals are used at intersections to control the movement of bicycles. While standard vehicular signals can control the movement of people on bicycles (bicycles are considered vehicles in the uniform vehicle code), in the U.S. and nearly every other application internationally, they most often consist of a signal with green, yellow and red bicycle symbols in the face. A photo of a typical bicycle signal showing the red, yellow and green symbol displays is shown in Figure 1. The signal housing, backplates, and mounting practices are similar, and often identical to, motor vehicle signals. The signal face with the bicycle symbol is often the only uniquely distinguishing feature. Bicycle signals are primarily used to separate bicycle movements from other conflicting movements (vehicle, pedestrian, transit) or to provide priority to bicycle movements via a leading bicycle interval or a split leading bike interval. They are also useful in situations where the bike lane is to the right (or left) of the exclusive turn lane and generally required to make two-way counter-flow bicycle facilities operate safely. They have been common tools in European low- stress bicycling networks for some time, where cycling is popular. 4
Credit: P. Singleton, used by permission Figure 1. Typical Red-Yellow-Green Bicycle Signal Faces (Portland, OR) The first application of bicycle signals in the U.S. is believed to have been in 1994 in Davis, CA, at the intersection of Russell Boulevard and Sycamore Lane (Pelz et al., 1996). Sometime later following the experiment in Davis, bicycle signals with the bicycle symbol in the face were included in the 2002 update to the California Traffic Manual (1996) and subsequently adopted in the California MUTCD (2006). Nationally, although the MUTCD contained provisions for circular signal indications to control bicycle movements, bicycle symbols in the signal face were not permitted until the âInterim Approval for Optional Use of a Bicycle Signal Face (IA-16)â issued in 2013 (FHWA, 2013). Interim Approval allows for the use of a traffic control device that is not in the MUTCD before it is considered in official rulemaking actions. Any jurisdiction that wants to use the bicycle symbol in the signal face must still submit a written request to the FHWA and comply with all provisions of the approval process as stated in in Section 1A.10 of the MUTCD. Project Objectives Prior to IA-16, the use of bicycle-specific signals in the U.S. was limited to a few jurisdictions (Monsere et al., 2013). However, in recent years, the number of installations has grown rapidly. This research identified over 500 intersections using bicycle signals in a variety of contexts. Despite the recent approval and practice, questions remain about the road userâs understanding of the bicycle signal face. The objective of this research was to summarize and synthesize the U.S. experience with bicycle signal installations to identify any remaining gaps in understanding road user comprehension and compliance with bicycle signals that could be effectively addressed through further research. Overview of Project by Tasks To accomplish the objectives, the project had five tasks: Task 1. Review of Existing Published Research; Task 2. Collect Information on Installations of Bicycle Signal Faces; 5
Task 3. Conduct Select Interviews with Key Agency Staff; Task 4. Develop Recommendations for Targeted Research; and Task 5. Final Report. Purpose and Organization of Report The purpose of this report is to document the results of the projectâs tasks and present the identified research gaps. The remainder of the report is organized as follows. Chapter 2: Background and Literature Review provides a brief review of the human factors concepts of visibility, comprehension, compliance, and driver error focused on traffic signal faces. Additionally, a review of the literature, including published evaluation reports and blog posts that relate to bicycle signals with a focus on comprehension and visibility of signal-type traffic control devices, is provided. Chapter 3: State of the Practice and Inventory describes the current design guidance and the results of the inventory of intersections in the U.S. with traffic signals that use the bicycle symbol. Chapter 4: Key Agency Interviews documents the results of interviews with agency staff experienced with designing and operating traffic signals for bicycles. Finally, Chapter 5: Identified Research Gaps presents the research needs that emerged to improve road user understanding of bicycle signal faces on traffic signals. Appendix A is a list of the intersections with bicycle signals that were inventoried. Appendix B is the data collection protocol and method. Appendix C is the research needs statements in the AASHTO/NCHRP format. 6
