August 4, 2011 By Sarah Rich
Pedaling through a traffic intersection on a bicycle sometimes doesn’t leave enough time to ride through the green light before the signal turns red. So a few cities in California are testing a detection device that keeps cyclists in the green.
Last year Pleasanton, Calif., began testing the Intersector, a “radar-style detection device,” at a traffic intersection. The technology distinguishes between bicycles and vehicles passing through street intersections.
The Intersector uses microwave technology to measure the length and speed of an object approaching the mounted device and uses that data to determine if the object is a bicycle or vehicle, said Mike Tassano, Pleasanton’s deputy director of community development and transportation. The Intersector, which connects to the traffic signal controller, relays that information to the controller, which calculates how much green light time the vehicles and bicycles need to pass through the intersection.
“The Intersector plugs into our traffic signal controller in the same way as any other detection,” Tassano said. “It’s physically wired back into our controller, and there’s an input directly into the controller.”
Bicycles stopped at a red light are identified by the Intersector and receive 14 seconds of green light time to pass through, whereas vehicles stopped at a red light receive four seconds.
If the traffic light is already green and a bicycle comes through, the cyclist receives an extension pass-through time of about five additional seconds. For vehicles, the extension time is two additional seconds.
Methods for Identifying Traffic
Tassano said a big reason why Pleasanton tested the Intersector is because in 2008 California passed AB 1581, a law requiring cities and counties — upon first replacement of traffic-actuated signals — to install signals that can identify motorcycles and bicycles on the road.
The city purchased the test unit through Western Pacific Signal, based in San Leandro, Calif. The units are manufactured by MS Sedco, which specializes in door and traffic control products. Each unit is priced between $4,000 and $5,000.
Other California cities, such as Redding, Monterey, Oakley, Oroville and Folsom — and Contra Costa County — have also purchased an Intersector, according to Western Pacific Signal.
Tassano said the city procured an Intersector with sales tax money issued through the state Transportation Development Act.
After the new traffic management technology’s test phase was complete, Pleasanton officials decided to expand the project. Seven Intersector units have been placed on four intersections along one corridor in Pleasanton. The city also purchased four more units, but they haven’t been installed yet.
Pleasanton currently also uses two well established traffic identification technologies: inductive loops, which are metal detectors in the ground that tell the traffic signal controller when there’s a vehicle present; and video camera detection, which identifies bicycles and vehicles when it sees a change in pixels.
But inductive loops don’t reliably identify bicycles, Tassano said, because cyclists must ride in a very specific location in order to be detected. And since there’s no metal in carbon fiber bicycles, they aren’t detected by inductive loops.
By comparison, Tassano said video detection identifies bicycles no matter what they’re made of, as long as they’re in the lane being recorded. The Intersector takes detection a step further by distinguishing whether the detected object is a bicycle or vehicle.
System Not Perfected
He said a drawback to the Intersector is that each device only detects four channels at once: a car turning left, a bike turning left, a car driving through the intersection and a bike riding through the intersection. With video camera detection, 16 channels are detected.
“If we want to maintain that same level of counting and detection, we can’t use these microwave units alone. They don’t have that versatility yet,” Tassano explained. “But from a detection standpoint they’re fine.”
The microwave detection device also isn’t capable of transmitting an image like a video camera does, but Pleasanton officials are hopeful that future Intersector models will include that feature as well as more detection channels.
Gary Mitchell, Folsom, Calif.’s traffic maintenance supervisor, said the city initially trialed two Intersector units at one intersection in September 2010. Two months ago, the units were moved to functioning and operational mode.
So far, the city has mixed feelings about the technology.
“It has, of course, great potential and it has the capability of discerning bikes, which is a great feature that we can make allowances for cyclists,” Mitchell said. “The problem is it’s not foolproof and you have to make certain assumptions with it.” Mitchell said it’s been Folsom’s experience that the units can be overly sensitive and detect pedestrians as vehicles. For that reason, Folsom isn’t ready to do a wide deployment of the technology.
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