What does the FHWA MUTCD IA-16 state about timing and phasing?
Operation of Bicycle Signal Faces:
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:
The minimum duration of the yellow change interval shall be 3 seconds.
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.
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.
The following are among the applications of bicycle signal faces that shall not be permitted under IA-16:
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:
Figure 5. Example of a green wave bicycle signal sign. Source: SFMTA.
NACTO recommends 60 – 90 seconds for quicker serviceability on bike-heavy approaches
Other jurisdictions govern cycle length by vehicular demand unless bicycle demand is high enough to warrant setting the cycle length to address cyclist demand more specifically
The city of Davis, California (Davis, CA) utilizes a 12-second minimum green for bike-heavy approaches for slower start up times from bikes
State of California MUTCD CA MUTCD | Caltrans) has a formula for minimum green for any phase where bicycle usage is legal, based upon the width of the intersection. They also require that all detection shall be capable of detecting bicycles unless the phase is on permanent recall. The provision is highlighted as follows: For all phases, the sum of the minimum green, plus the yellow change interval, plus any red clearance interval, should be sufficient to allow a bicyclist riding a bicycle 6 feet (1.8 meters) long to clear the last conflicting lane at a speed of 14.7 feet/sec (4.5 meters/second) plus an additional effective start-up time of 6 seconds, according to the following formula:
Gmin + Y + Rclear ≥ 6 sec + (W+6 feet)/14.7 feet/sec,
Gmin + Y + Rclear ≥ 6 sec + (W+1.8 meters)/4.5 meters/sec (metric),
Gmin = Length of minimum green interval (sec)
Y = Length of yellow interval (sec)
Rclear = Length of red clearance interval (sec)
W = Distance from limit line to far side of last conflicting lane (feet or meters)
Depending on demand should determine your max green time, can run concurrently with vehicular max green
Davis, CA utilizes a 25-second max for all bicycle signals
Treat as you would vehicular green time extension (2 to 3 seconds). Detection must support this operation
Yellow Change: Min 3, Max 6 seconds per IA-16
MnDOT utilizes yellow calculated for motor vehicles because “motor vehicles have higher speeds and lower deceleration rates than bicycles.”
Under MnDOT, if a bicycle signal is used exclusively for a bicycle movement, a 3-second yellow change interval should be used. This provides significant reaction and stopping time for a bicyclist traveling up to 15 mph (24 kph) and matches the Mn MUTCD minimum vehicle yellow change interval.
Red Clearance: Greater time frame is used since bicycles clear intersections slower.
The city of Davis, California utilizes 2 seconds
MnDOT does not recommend utilizing the calculation for motor vehicles for bicycles because they are slower
Red extensions can be utilized for larger intersections but require detection
MnDOT utilizes the equation shown in Exhibit 4-22 for min length of phase
Other jurisdictions link this time to the vehicular phase length
Bicycle progression ideal for around 12-15 mph (19 - 24 kph)
Figure 6. Bicycle signal faces at Rio Grande and 24th Streets. Source: Austin Transportation Department Flickr.
Bicycle phases will be operated much like pedestrian phases and run concurrently with non-conflicting vehicular phase
Recall can be assigned to a bicycle phase as well
Blank-out signs can be utilized during bicycle phases (no right turn, no left turns for vehicles)
LBI: Lead Bike Interval – give bicyclists a head start (3 seconds) before vehicles go
Utilized where peak hour vehicular right turn volume is over 150 vehicles
Two-way protected bike lanes where contraflow bicycle movement or increased conflict points warrant protected operation
Denver Bikeway Design Guidelines page 67 expands on this in more detail