Bicycling-supportive signal operations are not limited to bike signal hardware. With or without dedicated bike signals, modern traffic signal operation best practices can be applied to manage multimodal urban streets.
Signal Timing for Bikeways
All signalized intersections, regardless of whether they have bike signals, must provide sufficient time for people on bikes to clear the last conflicting lane. This total time includes the minimum green, the yellow change interval, and the red clearance interval.
Green intervals may be as short as four seconds, with a preferred minimum along bikeways of eight seconds. Longer minimum green times may be appropriate for larger or more intersections; use engineering judgment and account for land use, grade, and anticipated or current bike volumes. Bikes typically require longer time than motor vehicles because they accelerate at a much slower rate than motor vehicles. An additional six seconds of “start-up” time may also be added to account for the slower acceleration speed. Where bike signals are not used, the minimum green time for bikes can be part of the concurrent vehicular movement.
Yellow change intervals based on motor vehicles are typically sufficient for bikes. Do not rely on the yellow interval to clear bikes through the intersection. Where bike signals are used, the minimum yellow change interval is three seconds1 and can range up to six seconds depending on engineering judgment.
Red clearances are typically longer for people on bikes than for motor vehicles. The primary factors in choosing an appropriate clearance interval are bike travel speed and intersection width. At a minimum, the bike red clearance interval should be sufficient to accommodate the 15th percentile biking speed. This is consistent with typical practice for calculating pedestrian clearance intervals. Large intersections with long crossings will necessitate longer red bike clearance intervals.
Calculate the total red bike clearance interval (Ci) in seconds based on the following equation, where V represents bike speeds in ft/second (or m/second) and W represents the intersection width in ft or m:
Bike speeds (V) at relatively flat intersections can be assumed to be 9 mph or 14.5 ft/second (14.4 km/h or 4.4 m/second) in the absence of local data. On uphill approaches and where there are more young people on bikes and scooters, provide more time. Field measurements and speed studies can be used to inform specific intersections.
Intersection width (W) should be calculated from the intersection entry (i.e., the stop line, or crosswalk in the absence of a stop line) through the last lane carrying through traffic.
Consider implementing a red extension for bikes at very large or complex intersections. This typically requires bike detection during the yellow change interval.
Bike-Friendly Signal Progression
Bike-friendly signal progression minimizes how often people on bikes stop for red lights on a bikeway. Signal progression improves overall travel times for people on bikes even if delays are felt at one intersection along the bikeway.
Bike-friendly signal progression should be considered wherever a signal progression is in use in an urban setting and should be prioritized on streets with bikeways. Bike-friendly progressions are easiest to implement on one-way streets but can be implemented on two-way streets using modern techniques.
Typical bike progression speeds will vary based on grade and the use of electric bikes or other powered micromobility options. Progression speeds between 10 mph and 18 mph2 are often compatible with bike and transit speeds on urban streets and enhance bus reliability in the absence of active transit signal priority.
Bike signal progression speed is typically lower than the speed limit. This can help disincentivize unsafe motor vehicle speeds. Where signal progression is much slower than the speed limit, consider implementing a slower speed zone along the bikeway. Signs advising drivers of signal progression can help organize traffic flows.
- Federal Highway Administration. Manual on Uniform Traffic Control Devices, 11th Edition. USDOT, 2023: Section 4H.11.https://mutcd.fhwa.dot.gov/pdfs/11th_Edition/part4.pdf. ↩︎
- “10 mph is a comfortable speed for the general population; more confident cyclists may travel around 15 mph.”
Federal Highway Administration. Separated Bike Lane Planning and Design Guide. USDOT, 2015. https://www.fhwa.dot.gov/environment/bicycle_pedestrian/publications/separated_bikelane_pdg/. ↩︎