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Traffic Signal Cameras

This page last updated January 31, 2024

Over the past couple of decades, cameras at traffic signals have become ubiquitous. During the same period, red-light enforcement cameras have been installed in many locations, and there has been much publicity about them. As a result, many people believe that all the cameras they see at traffic signals are enforcement cameras. However, this is usually not the case. Below are pictures of the various cameras you'll see at traffic signals, an explanation of their purpose, and a discussion of red-light cameras in Texas.


Traffic detection camera

This is the most common camera type in use at intersections nowadays, and the one most people (including the media) often observe and mistake for a red-light camera. This camera, however, is actually a video image vehicle detection system (VIVDS). These cameras are used by the traffic signal controller computer to determine the presence of vehicles so that it can change the signals accordingly. This function used to be performed by inductive loop detectors in the pavement (and, in many places, still is.) However, the cameras are more cost-effective and flexible than loop detectors, which are fairly expensive to install, have a somewhat high failure rate, have limited capabilities compared to video recognition, and cannot be easily reconfigured if needed.

VIVDS camera
VIVDS camera
The way these cameras work is fairly simple. The camera is mounted so that it has a view of the approach road that it will be monitoring. Once in place, an engineer at the system console draws "detection zones" within the view range of the camera of the areas that need to watched for traffic. (If you've ever configured home security camera detection zones, this is essentially the same thing.) The computer then monitors those zones and when it detects a significant change in the image of that area (indicating the presence of a vehicle), it notifies the signal controller. The signal controller then uses that data to make the necessary decisions for changing the signals or timings. And, in many cases, these cameras can also be accessed remotely by engineers to see what's going on at an intersection if an issue is reported or detected.

Aside from their use at signals, VIVDS cameras are also used to monitor traffic levels and perform traffic counts.

Although these cameras are not red-light enforcement cameras per se, VIVDS cameras are often used in red-light camera installations as the mechanism to detect when vehicles have entered the intersection. They may be dedicated to that purpose (i.e. separate from the signal controller cameras) or they may serve both purposes. However, it's important to remember that the presence of these cameras in most cases does not mean the intersection has photographic red-light enforcement; see the "red-light enforcement cameras" section below to see what those cameras look like.

One drawback of VIVDS cameras is that they are often not effective during periods of inclement weather, so in many cases, they are now being replaced with acoustic, microwave, infrared, radar, and ultrasonic detectors. These look like small white panels or boxes mounted on the signal poles.

Signal preemption receiver

This is not even a camera, but rather an infrared receiver. These are part of a traffic signal preemption system that allows emergency vehicles, and sometimes public transportation vehicles, to request a green signal as they approach an intersection.

MIRT receiver
MIRT receiver
With these systems, the emergency or transit vehicle has a forward-facing mobile infrared transmitter (MIRT) that, when activated, sends out a pulsed infrared signal. As the vehicle approaches within about 2,000 feet of a preemption-equipped intersection, the device you see pictured here detects the infrared signal and notifies the signal controller. For emergency vehicles, the controller then initiates a preemptive stop phase for all directions except the one from which the emergency vehicle is approaching. It then changes the signals to green for the approaching emergency vehicle to clear any traffic queues and give that vehicle full right-of-way. It holds the signals green until the vehicle clears the intersection, at which point the signals return to normal operation. For public transit vehicles, it will either hold a green signal a little longer, or accelerate changing to a green in order to help the transit vehicle maintain its schedule.

In many places, these are being retired and replaced with GPS-based preemption systems. In those systems, the authorized vehicles send their current location to a centralized computer constantly, which then notifies the signals along their route to change as they approach.

Red-light enforcement cameras

These are actual red-light enforcement cameras. The assembly at the far left is a typical modern red-light camera, while the green boxy one is an older style but still in use in some places.

Red light cameras collage
Red light cameras and sign
These cameras sit a short distance before the intersection on the approach road, facing toward the intersection. An inductive loop detector or a VIVDS camera monitors the area just beyond the stop line. When the signal turns red, the detector is activated. When it detects a vehicle passing the stop line, it signals the red-light camera, which then takes two or more pictures of the vehicle, usually with a telltale camera flash. The camera is focused on the violation area so that it has a clear view of the vehicle, its license plate, and the signal. Additionally, the controller timestamps the image and records other pertinent details, such as location, direction of travel, and length of time the signal was red. Many cameras now also collect a short amount of video in conjunction with the still frame photos to help validate violations.

Images and recordings are then retrieved by or transmitted to the law enforcement agency with jurisdiction over that intersection or their contractor for review. In cases where the images clearly show a violation, a citation is sent to the registered owner of the vehicle. Photos of non-violations or of situations that are less definitive are discarded.

In Texas and many other places, a sign similar to the one shown here is required to be placed on the approach to an intersection with red-light enforcement cameras.

Status of red-light cameras in Texas
Red-light enforcement cameras started coming into use in Texas around 2003, and a law that clarified their use was passed in 2007. That law required an engineering study before installing such cameras, and required the installation of signs warning of photo enforcement.

After many years of public push back, the Legislature passed a law in 2019 that banned enforcement cameras, and nearly all cities in Texas scrapped their red-light camera programs as a result. But the law grandfathered cities with existing contracts that didn't have a termination clause, allowing them to continue their use until the contract expires. By the end of 2019, only four cities still had active cameras: Amarillo, Balcones Heights, Humble, and Leon Valley. Amarillo's program ended in August of 2022. Humble and Balcones Heights are scheduled to end in 2024. Leon Valley, however has a contract through 2039, but local leaders there are looking for ways to possibly terminate their contract before then.

Red light camera tickets
There is a lot of misinformation about what can happen if you get a ticket in one of the remaining places with the cameras, so here is an explanation of what was and is now allowed under the law in Texas.

Before the 2019 law, red-light camera tickets were civil violations, much like most parking tickets. You could never be arrested for not paying it, and it would not go on your driving record. However, it could be reported to a credit bureau, and your vehicle registration could be denied.

But the Legislature has done away with all of that. The 2007 law already prevented reporting of unpaid red-light cameras to credit bureaus (but it can still go to a collection agency), and the 2019 law prohibits the Texas DMV and county tax offices from refusing to register any vehicles that have outstanding red-light camera violations.

So to summarize:

So, it appears there are no legal or financial repercussions if you don't pay these tickets. But, if you want to avoid the hassle of getting violation letters or collection calls, or if you just feel a moral obligation to pay, then that's up to you.

A link to the 2019 bill that outlawed red-light cameras is in the "Other sites of interest" section below, along with a report from the Legislative Budget Board in 2013 giving the status of red-light camera laws and operations in Texas at that time.

Other sites of interest

Image Sensing Systems - Video Detection Products
Wikipedia: Traffic signal preemption
Texas House Bill 1631 (2019 law that banned enforcement cameras)
2013 Legislative Budget Board report on red-light cameras