Traffic Control FAQ
Do the traffic signals in Coppell run on a fixed time or is there something that senses the car?
Most of Coppell's signals are "actuated", which means that they sense when a vehicle approaches an intersection or knows when a vehicle is waiting for the light to change. This is not true at all intersections. Denton Tap Rd traffic lights are synchronized. This means that once a vehicle on Denton Tap passes through a green light and maintains the posted speed limit it should be able to approach other intersections with a green light. The lights between Dividend Dr. and Natches Trace are all connected in a synchronized system.
How do these sensors work?
Coppell and a majority of other cities use "loops" to detect vehicles. Two kinds of loops are currently in use in our city streets:
Inductance Loops
Inductance loops require saw-cuts into the pavement typically in a rectangular shape. Wire is then laid into the saw-cuts in a layered continuous loop. Power is applied through an amplifier in the traffic signal cabinet to the wires in the pavement. The result is a fairly stable electric field. The loop's field remains stable until a large metal object such as a car disturbs that field. The disturbance is what is actually sensed by the signal.
Video Detection
The other type of loop is actually drawn "virtually" for the newest type of detection - video. A video camera is mounted on the mast arm above the traffic signal but does not move or record images. Video detection software allows the programmer to set the area where sensing of vehicles is desired. The rectangle displayed on the monitor is visually similar to the saw-cuts on the pavement used for induction loops. The software is set to sense an approaching vehicle in that selected area by detecting changes in the picture or other disturbances in the pixels. When a vehicle is sensed, the signal light will then change.
Where are these "loops" located?
Loops are typically located at, behind, or otherwise near the stop bar which is the pavement marking indicating where vehicles should stop when the traffic signal is red. When vehicles do not stop behind the stop bar, it is likely that the traffic signal may not sense the vehicle's presence. At some locations where motorists consistently have the tendency to stop beyond the stop bar, a sign is installed to indicate the point where the loop will detect the vehicle. These loops, along with others on the approach to the intersection (at some locations), also act as green indication extenders up to a preset limit programmed.
How can I get a traffic signal installed at a particular intersection?
The intersection must first meet certain minimum criteria specified by the Texas Manual on Uniform Traffic Control Devices. The first criteria is that an engineering study of the intersection must be performed. The engineer looks at things such as traffic volumes, traffic delay, pedestrian volumes, accident history, road alignment (visibility), etc. The engineer's investigation may provide alternate solutions if the study does not warrant a traffic signal. These save the taxpayer unnecessary expense and can usually be acted upon more quickly. Contact the Engineering Department at engineer@coppelltx.gov.
If the intersection does warrant a traffic signal, then the process of obtaining funding begins. The entire process may seem lengthy, but it has been shown that installing a signal where it is not warranted can be worse than not having one.
Why does the pedestrian WALK signal only light up for 4 to 6 seconds?
Walk is displayed four to six seconds to tell you when to step off the curb and begin crossing the street. WALK ends and DON'T WALK flashes long enough for you to finish crossing the street. When DON'T WALK stops flashing opposing traffic has the right-of-way and you are not protected.
Rules to help you use the WALK signal:
- Push the pedestrian push button once and wait for the WALK signal. Note: Pushing the button repeatedly does not help speed up the signal.
- Enter the street only when you see the WALK displayed.
- Be out of the street when the DON'T WALK signal stops flashing.