Sunday, April 29, 2007
Insensitive traffic sensors
Christian Trejbal
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From the RoundTable blog
Bicyclists really don't find much love on the streets of the New River Valley.
That thought occurred to me again a few weeks ago as I was driving to work along Franklin Avenue in Christiansburg. I had stopped at one of the interminable traffic lights among the strip malls and big-box stores at the north end of town. Glancing to my right, I saw a bicyclist waiting to make a left turn onto Franklin.
I drive through these intersections several times per day, so I have a good sense of the lights' rhythms and foibles. If someone wants to make a left, he has to trigger the sensors to get an arrow.
Then it happened, or rather it did not. The light stayed red for the bicyclist and switched to green for me. I paused for a second and waved him through -- there was not much traffic that early -- but he declined.
I went on my way, but the rider nagged at the back of my brain.
There he was, obeying the law, and he got stiffed. Motorists often complain about bicyclists not following the rules of the road. Sometimes those complaints are justified; sometimes they are not.
The law requires bikers to follow pretty much the same rules as drivers of any vehicle. Bikers deserve the same respect.
The poor bike rider sits in the left turn lane, waiting and waiting for a green arrow. Then what? Look both ways for a break in traffic and run the light? Get off the bike, pull over to the side and walk across like a pedestrian? Risk a ticket or forfeit the right to be on the road. Some choice.
When I was learning to drive, my father used to tell me there were pressure plates under the pavement at lights to detect the weight of a car.
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Pressure plates, it turns out, are old school.
According to Wayne Nelson, director of Christiansburg's Engineering and Public Works Department, the town cuts loops into the pavement and lays wires that emit a magnetic field. When a big hunk of metal like a car interrupts the field, the sensors know to change the light.
"The only issue I've ever heard is that people who ride motorcycles say [the sensors] have a hard time picking them up," he said. "I've never heard of a bicyclist complaining."
If the magnetic field cannot notice a motorcycle, it sure is not going to sense a bike. Bicyclists are just less likely to complain. Most are calloused from being treated as second-class road users.
They take vehicles off the road, do their part to reduce greenhouse gas emissions, keep in shape, and still drivers dump on them. I do not even own a bicycle, but I respect the hell out of the people who ride them whenever they can.
Anyway, Nelson said, Christiansburg does not maintain the intersections on Franklin Avenue. The Virginia Department of Transportation does.
Chris McDonald, VDOT regional traffic engineer, explained that the department installs magnetic loops as well as two other systems depending on the intersection.
One system uses cameras mounted near the lights. The images feed into an artificial intelligence system that monitors the grayscale color of the road surface. When something changes the color in the image, it knows to change the light. As long as a car is not the exact same color as the road, there is no problem.
The other detector is a microwave emitter that detects objects in the road space. Put a big enough vehicle there and it will actuate the signal.
The trick is tweaking the sensitivity to pick up something as small as a bike and rider.
"Like anything else, there's some fine-tuning adjustments," McDonald said. "We do that all the time."
He suggested any bicyclist who has a problem with a particular light contact VDOT or the town.
Which is fine, but what about the biker stuck at the light on Franklin? Well, he is out of luck. "Definitely don't break the law," McDonald cautioned.
Society is still learning to deal with the growing popularity of bicycles as a serious means of transportation. We all benefit from riders' pedaling. They should not have to call and notify transportation officials of a problem. Lights should just work as well for them as they do for cars.
Christiansburg, Blacksburg and VDOT have been replacing their incandescent traffic lights with LEDs. The new lights save massive amounts of electricity. McDonald reports, for example, that electric bills for traffic signals are down as much as 80 percent.
Cheers for saving energy and taxpayer dollars.
Christian Trejbal is an editorial writer for The Roanoke Times based in the New River Valley bureau in Christiansburg.
