Bicycle Detection and Signalization
By Alyssa Sherman, Tech Transfer Program
Detection of bicyclists at signalized intersections can improve efficiency, decrease delay to bicyclists, and discourage red light running by cyclists without causing inordinate delays to motorists. Many California cities have already implemented bicycle detection devices. Bicycle detection at intersections can be accomplished using several technologies; the most widely used are loop detectors and video detectors.
At intersections with extremely large volumes of bicycle traffic, dedicated bicycle signal heads are another possibility. The city of Davis, California has installed the first bike signals in the country.
Well placed loop detectors with pavement markings are currently the most reliable technology for bicycle detection. Standard loop detectors will detect bicyclists, but the sensitivity must be adjusted so that bicyclists are detected, and the loops must be placed in a location where a bicyclist's movements can be registered. Detection using loop detectors does not depend on the presence of conductive metals as commonly thought. Instead, most in-pavement loop detectors commonly used today are inductive loops, which are triggered by a break in the magnetic field. Therefore, it does not necessarily require a heavy metal frame to be detected by these mechanisms. Previous research by Dr. Ken Courage at the University of Florida has indicated that non-ferrous metals and composites can work equally well. The Caltrans Type D loop configurations are generally considered an effective means for detection of small vehicles like motorcycles and bicycles. In California, cities including Bakersfield, Santa Cruz, Davis, and Palo Alto have adjusted loop detectors to detect bicycles.
In its Online Safety Toolbox, the Metropolitan Transportation Commission (MTC) mentions that loop detectors are ineffective if cyclists don't know where to position themselves, and inconsistency in placement or presence of stencils could confuse cyclists. However, these problems may be avoided by adhering to federal and state requirements for pavement markings accompanying bicycle-sensitive loop detectors, found in Chapter 9 of the MUTCD and Part 9 of the California Supplement.
To cut down on bicyclist confusion, many cities that use loop detectors for bicycle detection—including Bakersfield, Santa Cruz, and Palo Alto—have provided online tip sheets for bicyclists that describe "how to turn red lights green." For a model of loop detector-bicycle interaction, consult Design Considerations for Detecting Bicycles with Inductive Loop Detectors (See resources section in the sidebar for reference information).
Video detection can pick up a bicycle's presence at an intersection over a larger area. A video detection setup consists of a video detector usually mounted on a 4' riser pole or a mainline pole, and a computer with video image processing capability. In this system, installation is done above ground, minimizing lane closures. Existing video detectors have a flexible detector layout allowing for reprogramming of detection zones in a matter of minutes.
A recent paper describing research performed in Santa Clara County concluded that the video detection process had difficulties in detecting bicycles in darkness and resulted in occasional false calls due to vehicle shadows appearing on the bicycle lane, but that newer cameras might have corrected the problems. (Adaptive Signal Timing for Bicycles). See the resources section at the end of this article for reference information. The city of Walnut Creek, California, is currently testing video detection, citing the ease of maintenance and flexibility of the cameras as positive aspects of the system.
Bicycle Signal Heads
The City of Davis, home to UC Davis, has gained national preeminence in bikeway planning and design. In a city with a population of 64,000 residents, there are an estimated 60,000 bicycles. The city estimates that 17 percent of all journeys to work take place on bicycle. According to the City of Davis Comprehensive Bicycle Plan:
"The city of Davis has been using a traffic control device for a number of years known as a "bicycle signal head." These are similar to a standard traffic signal, except that it uses red, yellow and green bike icons rather than red, yellow and green "balls." Bicycle signal heads are commonly used around the world in such places as the Netherlands, England, Germany, and China. The city of Davis began using this type of traffic signal to help expedite the safe movement of bicycles through the city's more heavily used intersections (one intersection where these are in use has had counts of more than 1,000 bicycles per hour). The city of Davis is the first city in the country to utilize this innovative traffic control device, and the city was the driving force in getting the California Vehicle Code changed in order for its use to be allowed on public streets. These new traffic signals have performed admirably since the city began using them on a trial basis in 1990. Bicycle circulation was enhanced and safety has been improved atlocations where these have been installed."
More information on the potential advantages and disadvantages of bicycle signal heads is also available in the MTC's Safety Toolbox.
Thank you to Timothy Bustos, Sr., Program Manager for Tech Transfer and former Bicycle and Pedestrian Coordinator for the city of Davis, for his comments and edits.
Every method of detection and signalization has its advantages and disadvantages. Consult these resources for more information on the topic and to learn from the experiences of others.
The Metropolitan Transportation Commission's Bicycle/Pedestrian Safety Toolbox
Adaptive Signal Timing for Bicycles
Santa Clara County research project presenting different methods of bicycle detection and discussion of bicycle speed.
Design Considerations for Detecting Bicycles with Inductive Loop Detectors
Develops model of loop detector/bicycle interaction.
The Use of Bicycle Signal Heads at Signalized Intersections
Discusses implementation of first bicycle signal heads in the US in Davis, CA.