Chapter 5 of the Texas Department of Public Safety Drivers handbook states that traffic signals help provide for the orderly movement of traffic. Drivers must obey these signals except when an officer is directing traffic.

I have been waiting at a red light for a long time. Why does it take so long for the light to turn green while other lights change in a shorter amount of time?

A traffic intersection operates in accordance with the amount of time that an engineer has programmed in the controller. This is called the cycle length. The cycle length can vary from 45 seconds to more than 120 seconds, depending on the location and the time of day. Higher levels of traffic tend to result in longer cycles, as do common pedestrian crossing points.

Do traffic signals detect the presence of cars waiting at an intersection?

Signalized Intersections are equipped with one of two vehicle detection devices: A loop detector or a video detector.

A loop detector creates an electromagnetic field that senses large metallic objects (vehicles). When a vehicle disrupts the field, its respective signal is changed at the next opportunity to allow that direction of traffic to proceed. Note: Motorcycles and some vehicles may not trigger the loop detector.

Video detectors, a newer technology, are cameras mounted above a signal that send an image back to a computer which determines if any vehicles are present at that camera’s intersection. When a vehicle is detected, its respective signal is changed at the next opportunity to allow that direction of traffic to proceed. Note: Video detectors are not red-light cameras and do not possess a precise resolution necessary to read license plates. Additional Information on the City’s Video Detection System.

Sometimes detector devices sense a car that has subsequently made a right turn, making the detector seem like it is malfunctioning. If you believe the detector at an intersection is malfunctioning (if it does not recognize a direction of traffic when cars are present, for instance), please report your concerns to 311.

How do some emergency vehicles get a light to change in their favor?

Some signalized intersections posses Emergency Vehicle Preemption receivers, mounted to the top of some signal poles. These devices allow for a disruption in the signal cycle for an emergency vehicle, reducing its travel time and protecting motorists from collisions. Vehicles with this capability are equipped with an emitter, which communicates with an intersection’s receiver. The receiver, when prompted, induces a light to change in favor of the emergency vehicle’s direction.

Are there tricks to inducing a green light, such as flashing my headlights off and on repeatedly or putting my car in reverse and driving forward again?

There is no device installed in traffic signals that responds to flickering lights or counts the number of cars waiting at an intersection.

Will pushing the pedestrian walk button several times make the signal change faster?

No. The walk button will send a call to the controller requesting the next available signal cycle be granted to the requested direction. In areas of high-level pedestrian activity (downtown), walk lights are automatically configured into the cycle, so the intersections do not possess walk buttons.

Why is the pedestrian walk light timing so short before it begins flashing?

Flashing walk lights the pedestrian equivalent of yellow lights. They are designed to ensure plenty of time for a person to finish crossing before the opposing direction’s light turns green. If a walk light is flashing when you arrive at an intersection, you should wait through the next cycle until another walk light appears.

Does the City use Stop Signs to control speeding?

No, stop signs are right-of-way control devices, not speed deterrents. Requiring all drivers (law-abiding or otherwise) to stop at unjustified stop signs would add unnecessary delay & fuel consumption to commutes. Some studies have shown that motorist compliance decreases at locations where signs are considered unjustified due to traffic volume. Speed humps and law enforcement are the tools most effective in reducing speed violations.

What should I do when I approach an intersection that is out or has no traffic signal indications?

If traffic controls are flashing or out altogether, make sure you come to a complete stop and that there are no approaching vehicles from your left. State law states that this type of situation the intersection should be treated as a 4 way or all way stop. You may legally have the right of way but you should be sure other drivers yield to you before proceeding. Remember pedestrians always have the right of way. Flashing or down signals increase the chance for collisions, so you should always exercise extra precautions when driving through them.

How do traffic signals work?

A couple of terms for signalized intersections…

Phase- A phase is a numbered designation used to define the direction of travel. For example, east bound direction of travel is phase 2, south bound phase 4, west bound phase 6, and north bound phase 8.

Cycle- A cycle is the length of time designated by an engineer for the completion of all phases. Example: 60 second cycle or 120 second cycle.

There are three types of signal operation in Houston: fixed-time, semi-actuated, and fully-activated…

Fixed-time operation is a predetermined amount of time is given to all directions or phases of an intersection. There are some cases where the traffic lights can be set to change to different cycle length during peak traffic hours. Fixed-time operations can be found in downtown, where traffic movements are fairly predictable and pedestrian walk lights are automatic. Currently less the hundred are in operation.

Semi-actuated operation uses vehicle detection devises to move between signal phases according to the amount of traffic detected. Detectors sense traffic on smaller streets and the length of each direction’s green light is automatically adjusted to maximize traffic flow through an intersection.

Actuated operation functions much like semi-actuated, but with vehicle detection on all directions of flow. Detectors re-determine the amount of time allotted to each phase (or direction) for each cycle.