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Signal Timing and Phasing for Bicycles

What does the FHWA MUTCD IA-16 state about timing and phasing?

Operation of Bicycle Signal Faces:

  1. Timing: The provisions of Section 4D.26 apply to the duration of the yellow change and the red clearance intervals of a bicycle signal phase except as follows:
    1. The minimum duration of the yellow change interval shall be 3 seconds.
    2. The maximum duration of the yellow change interval should be 6 seconds. The exclusive function of the yellow change interval shall be to warn bicyclists approaching a signalized location that their permission to proceed is being terminated after which they will be directed to stop. Providing enough clearance time for a bicyclist to travel through the intersection or conflict area is the purpose of the red clearance interval, not of the yellow change interval.
    3. If discernible non-concurrent activations or terminations of phases for motorized vehicular traffic and bicycle signal indications are necessary, visibility-limiting devices should be used on the bicycle signal face.

Prohibited Uses:

The following are among the applications of bicycle signal faces that shall not be permitted under IA-16:

  1. Exclusive Bicycle Phases that permit “Scramble” Phases: Bicycle signal faces shall not be used to provide a bicycle phase that stops all motorized vehicles and pedestrians at the signalized location in order to allow multiple bicycle movements from multiple conflicting directions.

One of the biggest issue designers face with IA-16 is that it does not permit any conflicting vehicle turn movements when the bicycle signal is green or yellow. This restriction can limit the application of bicycle signals because of the need to prohibit conflicting turning movements such as left or right turns (including turns on red) during the green bicycle signal phase.  In order to increase the use of bicycle signals to improve safety and compliance, enhance wayfinding, and provide more consistency for all users at signalized intersections numerous jurisdictions have been interested in softening this restriction or addressing it by experimenting with design treatments as discussed below under “Design Challenges in the United States.” As a result, there are pending requests to soften this restriction, but to date it has not been changed.  Many experiments sanctioned by FHWA are testing alternative treatments, as noted below.

Many different jurisdictions are testing and applying different means and methods for bicycle signal phasing and timing at their intersections. Also, many jurisdictions apply for and study variability in published practice. Different factors and conditions such as intersection size, demand, and detection play into how each jurisdiction handles the timing and phasing of their bicycle signals. As more testing and implementation has been done, more jurisdictions are publishing recommendations on proper operation of bicycle signal timing and phasing. More data is being published on minimum greens, clearance intervals, extension periods, leading intervals, cycle length, and even progression.

The following information outlines practices done by different jurisdictions around the country:

Green WaveFigure 5. Example of a green wave bicycle signal sign. Source: SFMTA.

Signal timing:

Rio GrandeFigure 6. Bicycle signal faces at Rio Grande and 24th Streets. Source: Austin Transportation Department Flickr.

Signal Phasing:

 

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