|All you need to know about traffic signals, and then some!|
|If all you know about traffic signals is that they are red, yellow and green, you've got a lot to learn! Here are a few pointers to make your trip through town a little faster.
For many years now, the traffic signals on major roads have been 'traffic actuated'. This means that there are sensors of one type or another that can tell if vehicles are approaching, or waiting at an intersection. These sensors notify the traffic signal controller, which is really a little computer. The controller then adjusts the signal timing according to traffic conditions. Most newer signals have this capability, even if they're not on a busy highway.
A basic understanding of how this all works can help you get a green light faster, or even make an already green light wait for you to get through it.
First of all, I'll give a quick description of the two most popular types of sensors. Look for them the next time you're out on the road.
The most common sensor is the 'loop detector'. This consists of a groove cut into the pavement, usually a fairly large rectanglular shape. Several wraps of copper wire are placed in the groove to form a large coil, or 'loop'. The groove is then filled in with asphalt or tar. They are easy to spot, especially in left turn lanes. The loop is connected to the traffic signal control box, and basically acts as a huge metal detector. A vehicle passing above the loop disturbs it's magnetic field, putting in a 'call' to the signal controller.
The latest detectors use television cameras. The cameras are mounted high up on the traffic light poles, usually aimed into oncoming traffic. They look similar to outdoor security cameras. The pictures from the camera go into the traffic signal control box, where a computer uses 'pattern recognition' or 'motion detection' software to determine if a vehicle is present. One camera can provide several seperate 'calls' to the signal controller, based on what lane(s) vehicles are in.
My most important point, especially for the 'loop detector' system, is to be sure to stop your car in the right place! The front bumper of your car should be about even with the white 'stop line' on the road, or the signal posts if there is no stop line. If you stop 20 feet back from the line, AS I SEE A LOT OF PEOPLE DO, chances are the signal will skip your turn! Same thing if you stop past the line. Some intersections with frontage roads have a sign that says "do not block intersection", and another stop line before the frontage road, but no sensor by that stop line. You could sit there all day at a red light!
At least one car has to be at the main stop line to trigger the signal.
Many signals are programmed to give a continuous green light to the busier of the two roads, unless a car approaches on the side road. If for any reason the sensor does not know that you drove up to the red light on the side road, YOU WILL NEVER GET A GREEN LIGHT! This could be for the reasons mentioned above, or it could be that the sensor is malfunctioning, which happens quite often (big problem for motorcycles). Sometimes, backing up a ways, then driving up again will trigger the light. But watch out if you get frustrated and go through the light, because you'll probably get a nasty ticket! (Been there, done that, argued with the cop, and wound up in jail!) (More on that in <police> ).
Most of these systems also have an additional sensor located a couple hundred feet back from the intersection. This serves to 'extend' the green light, usually about 7 seconds, to allow traffic that is already flowing to make it through the light without having to slam on the brakes. If you 'step on the gas' and make it to that sensor, you can ease off a little and still make the light! Of course there is a limit to how long the light can be extended. If other traffic is waiting, the light will eventually 'max out'.
You may have noticed that the left-turn arrow comes on only if there are cars in the left-turn lane. If you're going to use that lane, and it's empty, try to get there before the green light for the cross traffic turns yellow, and you should be next in line! Also, most left-turn lanes 'gap out' in only a couple seconds, so don't leave a big space between your car, and the one ahead of you, or the arrow will go yellow on you!
If you're approaching a red light and there is more than one straight-ahead lane, don't use the right-most lane to go straight. The sensor for the right lane often has about a 10 second delay programmed into it, in case you plan on making a right turn on the red light. But the inner lanes will put in a call for a green light immediately. Plus, you won't screw up the lane for someone else to make a right turn on the red light.
I'm running out of space here, but a lot more on this subject is on the way!!
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