Traffic Questions Answered
It didn’t take long at all to learn more about some of the things I mentioned in my “Green Light Go” post.
The best resource I found was Wikipedia under the “Traffic Light” page.
More sophisticated control systems use electronic sensor loops buried in the pavement to detect the presence of traffic waiting at the light, and thus can avoid giving the green light to an empty road while motorists on a different route are stopped. A timer is frequently used as a backup in case the sensors fail (they often do); an additional problem with sensor-based systems is that they may fail to detect vehicles such as motorcycles or bicycles and cause them to wait forever (or at least until a detectable vehicle also comes to wait for the light). The sensor loops typically work in the same fashion as metal detectors, small vehicles or those with low metal content may fail to be detected.
It is also commonplace to alter the control strategy of a traffic light based on the time of day and day of the week, or on other special circumstances (such as a major event causing extra traffic through an intersection).
I didn’t think about changing the settings to reflect the time of day or events happening. That is a great idea though. I remember how backwards the traffic would be when I was leaving high school. That many cars for something like that or a sporting event can change the flow of traffic for a pretty large area by everyone going at once. Here is another tidbit I thought was a good idea.
Attempts are often made to synchronize traffic lights so that drivers encounter long strings of green lights. This is done easily only on one-way streets with fairly constant levels of traffic. Two-way streets are often arranged to correspond with rush hours to speed the heavier volume direction. Congestion can often throw off any synchronization, however. In other cases, traffic lights are synchronized to prevent drivers from encountering a long string of green lights, in order to discourage speeding.
Steve read my post and dropped his 2 cents.
Zach, there’s two things involved: rudimentary cameras and something called “induction loops”.
The cameras don’t see details, but instead see objects. They detect objects moving through a “zone” of a lane headed to the intersection and maintain a green light to let traffic through or instead, trip the light from red to green as needed. They were developed in response to the poor performance of induction loops in their early form. Induction loops detect the metal of a car and trip the light, but with motorcycles (or cars that didn’t pull forward far enough) they didn’t work. Now the cameras do the job.
I am a bit suprised to learn that the cameras were so basic in nature. This little lesson will make speeding through red lights a lot more fun.
This entry was posted on Friday, September 23rd, 2005 at 1:38 pm and is filed under Thoughts. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
Brian September 28th, 2005 at 2:58 pm
“I am a bit suprised to learn that the cameras were so basic in nature. This little lesson will make speeding through red lights a lot more fun.”
Careful what city you’re in. In the Phoenix area they have cameras mounted on stoplights not to manage traffic flow, but specifically to take pics of red-light runners. They also like to park vans on the side of the road to snap pics of speeders. It’s much harder to talk your way out of a ticket when it just shows up in your mailbox. On the plus side, that camera will never find the dime bag in your glove box.