By Mary Ebeling
Managing traffic flow at intersections presents challenges, regardless of mode. But as the popularity of transportation bicycling continues to grow, traffic engineers, planners, and lawmakers are recognizing the need to incorporate bicycle-specific infrastructure into intersection designs. Currently 16 cities in the U.S. use bicycle-specific traffic signals. The signals better accommodate the specific needs of bicyclists, for instance, by allowing cyclists more time to clear intersections safely.
Bicycle-specific traffic signals may be installed in several different ways – as a stand-alone signal head or incorporated into the main traffic light. The National Association of City Transportation Officials (NACTO) provides excellent guidance for installing bike signals.
While widely used in Europe and Australia, the U.S has been slow to adopt bicycle-specific traffic signals. To date, only California has included this infrastructure in its street design manual, although a bill in Oregon currently under consideration would make bike signals a recognized option in the state as well. Portland, Oregon, already is implementing bicycle signals as a strategy to reduce conflicts between motorists and cyclists. Providing an exclusive signal display recognizes the differences between motor vehicles, bicycles, and pedestrians, and it separates bicycles from conflicting traffic movements.
The State of California approved the use of bicycle traffic signals in 1998, based primarily on data from the City of Davis, California, which concluded:
- Bicycle signals enhance safety by separating large volumes of bicycle and auto traffic;
- Bicycle signals cause minimal additional delay to motor vehicles;
- Bicycle signals are easy to comprehend by bicyclists and motorists;
- Bicycle traffic signals should be considered on a case-by-case basis, taking into account intersection geometry and bicycle and motor vehicle volumes.
NACTO provides detailed information and guidance for appropriate locations to install bicycle signal heads. Currently, bicycle signal heads are not incorporated into the federal Manual on Uniform Traffic Control Devices (MUTCD), though the National Committee on Uniform Traffic Control Devices has formed a Task Force that is considering adding guidance to the MUTCD on the use of bicycle signals.
NACTO notes that an “adequate clearance interval (i.e., the movement’s combined time for the yellow and all-red phases) shall be provided to ensure that bicyclists entering the intersection during the green phase have sufficient time to safely clear the intersection before conflicting movements receive a green indication.” Best practice from Davis, California, requires a minimum bicycle green time of 12 seconds and a maximum green time of 25 seconds. In addition the signal phase includes a two-second all-red interval at the end of this phase to help ensure intersection clearance.
Mary Ebeling is a Transportation Policy Analyst at SSTI.