What's Wrong With the Traffic Light?
First, remember: You're sharing the road with pedestrians... and they have the right-of way!
While WALK is on for pedestrians, vehicle traffic also may have a green light. As seen in the diagram at the right, with the crosswalk shown at the top of the intersection, cars may turn into a crosswalk from three directions, even though pedestrians have the right-of-way. Vehicles with a GREEN light (such as those at the left and right sides of the intersection) might turn left or right into the crosswalk. Vehicles with a RED light (such as the one just above the crosswalk in the diagram) are usually permitted to turn "right on red." However, vehicle traffic must always yield to pedestrians!
The cars in the figure at the right were waiting for the light to change. As the drawing indicates, patience and knowing where to stop for the light might put you ahead of less patient drivers who don't know or follow the road rules. In the picture at the left:
- The red car (waiting for the left-turn signal) will not change the light -- it has stopped beyond the area detectable by the intersection's signal controller. Unless someone pulls up behind this driver, he or she can end up waiting a long time!
- But the green car is waiting for the light to change in the proper location. Even though this car is "behind" the red one, it gets to proceed through the intersection much sooner.
Here in Tallahassee...
Law requires that the bumper or most forward part of the vehicle be behind the stop bar.
Where is the detection zone? Vehicle sensors are "loops" of wire embedded in the pavement. Typically, left turn loops are 60 feet long and those in through lanes are 20 feet long. They start at the stop bar on each approach as depicted in purple in the above drawing.
We are also deploying a relatively new technology, video detection, in which detection zones are drawn on the background of the static video of an approach to an intersection. When the background changes due to a vehicle's pulling into the detection zone, a signal is sent to the traffic signal controller, which causes the light to change eventually. This new video-based system uses the same size zones as the signal loops.
Main streets usually get more green time
While waiting for the light to change on a side street, remember that most traffic is moving on main streets.
What's a full timing cycle?
Major streets come together at some intersections. Each direction might get 60 seconds (or more) of GREEN time. Consider left turns, straight traffic, and yellow signal timing for each direction. A full cycle at a given intersection might take several minutes. When traffic in opposing directions is light, a couple of minutes' waiting can certainly seem like ten!
Traffic engineers attempt to move the greatest volume of traffic in the shortest amount of time.
Signals are usually programmed so that each intersection is "timed" to work with other intersections. While 2, 4, 8, 16, or however many cars are waiting for a light to change on a minor street, 16, 32, 64, or more cars might move along the major street. Based on traffic volume data (which varies from day to day), it is sometimes best to hold the minor street RED for a specific period of time (causing traffic to "stack up"), while allowing a greater volume of traffic to travel through GREEN signals on the major street.
Remember the effect of pedestrian signal timing.
A pedestrian may have activated a "WALK" signal. Pedestrian signal timing is the combination of both "WALK" and flashing "DON'T WALK." The pedestrian may still be crossing the intersection. However, once the signal is activated, it will come on even if the pedestrian has already crossed during a break in traffic.
Still think the timing is off?
RELAX! Report the problem to the City of Tallahassee Traffic Management Center at 891-2080.
(If a signal is completely out and you have a cell phone, dial *COP to be connected to the Tallahassee Police Department, which will dispatch one or more officers to assist with traffic control.)
About the information on this page:
Information here borrows heavily from a brochure available at the site of the International Municipal Signal Association (IMSA). The brochure was written and illustrated by Alan Poudrier, at one time a Traffic Signal Technician with the Okaloosa County (FL) Public Works Department. We are grateful to Mr. Poudrier for his generous permission to adapt the brochure's contents to our own purposes.