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Summary 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 or space for safety or other reasons. While standard vehicular signals can control the movement of people on bicycles, 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. Before the Federal Highway Administration (FHWA) issued Interim Approval-16 in 2013, use of the bicycle symbol in the signal face in the U.S. was limited to a few jurisdictions. In recent years, however, the number of installations has grown significantly. It is important to note that while an Interim Approval allows for the use of a traffic control device not in the Manual on Uniform Traffic Control Devices (MUTCD), jurisdictions must still submit a written request to the FHWA and comply with all provisions in order to use the bicycle symbol in the signal face. Despite the interim approval and increased use, 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. Three primary tasks were completed to accomplish these objectives: 1) a literature review, 2) an inventory of existing bicycle signal installations, and 3) interviews with key agency staff. The relevant literature was identified by searching TRID (Transport Research International Documentation) for the appropriate keywords. This literature was supplemented with MUTCD Request to Experiment (RTE) filings (which are approved experiments with traffic control devices not in the MUTCD), and final evaluation reports submitted to FHWA. Grey literature, including evaluation reports by public agencies, blog posts, and popular press stories, were also reviewed. The locations of bicycle signals were identified from an online survey and an existing list maintained by the bicycle technical committee of the National Committee on Uniform Traffic Control Devices. For the 511 intersections where the installation of a bicycle signal was verified, the research team collected data on year of installation, number of bicycle faces, mounting heights, distance from the stop line, use of arrows, lens diameter, use of colored housing or backplates, presence of visibility restricted louvers and a few other data elements, primarily by reviewing Google Streetview images. Structured interviews were conducted with key staff at 21 agencies, which included six state DOTs, 14 cities, and one county to explore their experiences and gather their input on research needs. The review of the literature found no published research studies that directly addressed visibility and comprehension of the bicycle signal face or the transferability of design assumptions from motor vehicle users. While the research found some anecdotal evidence of driver confusion with bicycle signals due to lack of separation between vehicular and bicycle traffic signal faces, none of the published evaluation reports found evidence of significant user confusion. Examples of research conducted for other traffic control devices such as light-rail transit signals, flashing yellow arrows, bus queue jump signals, and pedestrian countdown timers suggest methods and analysis techniques that could be applied to address research gaps related to bicycle signals. 1
The inventory documented an increasing number of installations of bicycle signals, particularly after 2013. The states with the most intersections with bicycle signals were New York (156), California (70), Illinois (40), Washington (51), Oregon (33), and Texas (26), with large cities in these states being the primary adopters. The research team assessed the primary purpose of using the signal control for bicycles. This assessment found that the most common uses of bicycle signals are to facilitate the contra-flow movement of a two-way bicycle lane and to provide separation when the bicycle lane is placed to the left of a left-turn lane or the right of a right-turn lane. Other purposes include facilitating bicycle connections to two-way facilities or paths, controlling contra- flow and diagonal bicycle movements, facilitating left-turns, and crossings for multiuse paths. Variations in practice suggest potential areas for additional guidance. Though IA-16 requires a second signal face for intersections when the primary signal face is more than 120 feet from the stop line, and suggests a second signal face for more than 80 feet, many installations used two signal heads for bicycles even when the distances to the stop bar were less than 120 feet. Most of the signal faces in the inventory met the horizontal and vertical separation from vehicular signal heads recommended in IA-16. Two-thirds of the lenses with the bicycle symbol in the inventory were 8 inches. Selection of lens size did not have an apparent relationship with visibility distance. The structured interview consisted of 25 questions on experience with bicycle signals, road user understanding, lens visibility and conspicuity, placement of the bicycle signal face, operations, and research needs. Several clear trends emerged from the interviews as potential research ideas which included: ⢠Guidance on ways to communicate with a person on a bicycle that their movement is protected or permissive and whether it conflicts with other road users. ⢠Techniques to differentiate the bicycle signal from motor vehicle signal heads. ⢠Placement of bicycle signals in relation to the driver line of sight. ⢠Guidance on appropriate distance for visibility when using a bicycle signal with a bicycle symbol face in the lens. ⢠Refinement of the specifications for display intensity and symbol design. ⢠Guidance on selection of lens size considering visibility distance, including 4-inch near-side signal heads. The agency interviews also identified other research needs not related to road user comprehension, including quantifying the tradeoffs associated with signal timing and phasing strategies for bicyclists, guidance on bicycle detection and feedback confirmation, and examination of current guidelines for the inclusion and duration of yellow change and red clearance intervals. Finally, the synthesis of the results from the literature review, inventory and interviews identified three research needs in the road userâs understanding of bicycle symbols in the signal face. In priority order, the research needs 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. 2
Research needs statements, describing the background, research objectives, and proposed tasks necessary to address the gaps were then developed. 3
