There was a lot of interest in last Friday’s post about bicycle detection for traffic lights at intersections, in which I uploaded a report about the state-of-the-art in 1985.
The diagram above shows inductive loop detectors often used at intersections to detect traffic and trigger a green signal light. Black shows you the shape of the cuts to look for in the pavement; yellow highlights where to place your rims. Yes, it’s ridiculous that a study in electrical engineering is required just to cross the street.
The induced loop detectors used 30 years ago are still commonplace today, but newer (and more expensive) technology is available. I’ve reported before on radar, ultrasonic, and video detectors that are specifically tuned for bicycles.
Video detection works well in California, but it’s not always the panacea often touted by cycling advocates. Video detectors are easily identifiable by the cylindrical camera housings mounted somewhere high above the intersection. If you have trouble triggering even video detectors, Steve in DFW explains their operation and provides good pointers. He notes, for example, that the road edge can often be beyond the field of view of the video camera. If you’re in the shoulder, the camera doesn’t see you. They also can’t see ninja cyclists operating their invisible bikes at night without lights. Again, special knowledge is sometimes required to cross the street.
You might remember Iteris and their SmartCycle bicycle detection system. All new video detection systems from Iteris come with the SmartCycle system installed, and SmartCycle is available as a free firmware upgrade on installed systems. This video explains how the system works.
Transportation planners often hesitate to lengthen the traffic signal green phase for cyclists because it messes up their traffic flow projections and intersection Level of Service for cars. This bike detection allows signals to increase this green phase time only when bikes trigger the green light, completely eliminating LOS as an excuse to change the timing.
Because multiple vendors now offer bicycle detection capabilities that change the green phase timing just for bikes, cycling advocates really should bug your local transportation departments to enable these capabilities in their traffic lights.