This is fairly accurate. The bar is inset with copper conductors, says Barrick, who has been working in the traffic control business since 1982.
The conductors create a magnetic field. When a car enters this field, the metal of the car should "deflect the lines of flux in the magnetic field and basically give the traffic signal controller a call for green."
However, simply breaking the magnetic field only momentarily will not trip the signal change, according to Barrick.
A car must break the flux of the magnetic field and stay there for a varying amount of time, depending on how busy the intersection is, the time of day, and the traffic coming in the opposite direction. This accounts for cars making right turns that do not need the light to change.
Magnetic field is the controller
Barrick notes that sometimes a car must only sit in the magnetic field for 3 seconds before signaling a light change.
Other times, such as along main highways, a car trying to enter the highway from a side street could have to sit in the magnetic field for up to 90 seconds.
If, at any time, the car leaves the stop-bar, according to Barrick, it cancels the call to the controller and the clock is reset.
The controller, though, is not a person sitting in a room full of television screens watching drivers as they approach lights as it seems to be in Hollywood movies. The controller is a stainless steel box that sits next to the intersection.
Inside the box is a computer that does not allow for two green lights to be given at once, controls the timing, and receives the signal from the stop-bar. It also controls the length of the green light, which varies from 12 seconds to 120 seconds, according to Barrick and depending on the traffic.
Barrick mentions several problems with the stop-bar and driving frustrations. First, he cites the lack of awareness of the way the stop-bar works.
"A lot of times, such as the intersection of Perryville Road and the bypass, the stop-bar is placed back a bit so trucks can make the left turn."
Closer is not better
Barrick says drivers pull forward beyond the stop-bar to be closer to the intersection but, in so doing, cancel the call, and the controller will no longer recognize that a car is waiting for a signal change. He also says that drivers on cell phones often are distracted and pull too far forward.
JoAnn Rice of Danville believes that traffic lights are signaled to change by "a combination of timers and sensors depending on traffic flow."
Rice also correctly thinks the sensors are buried in the ground at each intersection. However, she was not aware of the stop-bar and admits to sometimes pulling beyond the white line.
The biggest problem she sees is at Perryville Road and the bypass. "Sometimes the lights pass me on the cycles."
During heavy traffic times, controllers are set up to run a different program. A driver waiting to enter a main street from a side street typically waits longer between the morning hours of 7 and 9 and the evening hours of 4 to 6 than at any other time of day.
There are different types of traffic signals as well. Barrick says the signals along Main Street in Danville are on a simple timer system and the stop-bars do not have any effect on when one gets a signal.
"To better recognize your traffic signals as 'go lights' and not so much 'stop lights,'" Barrick suggests drivers pay attention to the stop-bar, stay inside the magnetic field until the light changes, and understand that at different times of day, the signals will be longer between changing. This should help to streamline the daily commute.
Kevin Duke is an intern at The Advocate-Messenger and a senior English and history major at Centre College.
