The Massachusetts Department of Transportation Project Development and Design Guide, published in 2006, is recognized as pioneering in its call for street design “from the outside in,” recognizing the need to provide for pedestrians and bicyclists. The Guide is explicit in its requirement that traffic signals work for bicyclists, but does not give detailed actuator specifications. This is in Section 6.3.2:
Traffic Control – Bicyclists are required by law to obey control devices at intersections. Therefore, traffic control devices need to account for bicycle activity. Traffic signals which operate using detection systems (such as loop detection, video camera, and microwave) must be designed and field tested to be sensitive to bicycles. Many of the aspects of traffic control described for motor vehicles (below) also apply to bicyclists.
The Massachusetts Highway Department document Bicycle Detection at Signalized Intersections, published in 1998 does get into specifics, including recommendations for quadrapole loops. The 1986 San Diego report, the definitive report on electromagnetic loop detectors, is cited as a reference. The Massachusetts document does include some recommendations which reflect an inadequate understanding of bicycle characteristics and operation, notably:
Bicycle markings should be placed to the right side of general purpose through lanes to conform to recommended bike-riding practice (allowing the faster accelerating cars to pass within the lane).
A bicyclist needs to actuate the signal when first to arrive at a red light. A bicyclist who waits near the left side of a through lane which also allows right turns can offer the courtesy to a motorist who arrives later to turn right legally on red. The bicyclist also avoids the risk of a “right hook” collision. The bicyclist can merge back to the right side of the lane (assuming that it is wide enough to share) once the light has changed.
The report later states that a detector should be placed
1. In a dedicated bicycle lane.
2. On the right side of the right travel lane.
3. On the left side of a left turn lane (if the lane is a shared use lane for left and through movements).
4. On the right side of a left turn lane (if lane is an exclusive left turn lane).
5. Just to the right of the centerline when turning left on an ordinary, two-lane street.Therefore, bicycle detection should be placed at locations described above. It is not practical to force bicyclists to ride in traffic situations where they are not comfortable or are in conflict with recommended bicycle safety practices. We suggest that each intersection be evaluated individually for bicycle detection.
Aside from the issue already described, this advice reflects concepts of lane use which have to some degree been superseded. A bicyclist who waits near the left side of a left turn lane risks having motorists pass on the right to turn left, forcing the bicyclist into oncoming traffic in the cross street. A bicyclist who waits near the right side of a left-turn lane risks having motorists overtake unsafely on the left. It is generally better for the bicyclist who arrives when the light is red to ride closer to the center of the lane, but the best position depends on conditions at a particular time and place. The best design practice is to install a detector which senses a bicyclist anywhere in the lane, for example the California D-type loop described in the San Diego report.
The document lists several types of detectors besides loop detectors: video, microwave/radar, sonic, magnetic — and magnetometers, the only one besides loop detectors to which it gives a strong recommendation; but in mentioning magnetic detection and magnetometers at all, it is mistaken, because aluminum bicycle and motorcycle rims are nonmagnetic and will not be detected.
I have another post describing national history of traffic signal actuators, here.
