How does Sacramento coordinate its traffic lights? Your question answered
Have you ever wondered how traffic lights know when to give you a signal?
Reader Nick Shepard asked Bee Curious, a community-driven series in which The Sacramento Bee’s service journalism team answers reader questions: How does the traffic light system work in Sacramento?
“In Sacramento traffic lights turn green at the same time as intersecting traffic turns red, with no delay,” Shepard wrote to Bee Curious. “This is the only place I’ve ever seen such a thing. Why is it this way in Sacramento?”
The why isn’t clear, Nick. But we can tell you how the city operates its system. Here’s what the city of Sacramento said on how the traffic lights function:
How do Sacramento traffic lights work?
The Traffic Operations Center located in City Hall at 915 I St., monitors traffic through the use of a computer-based traffic signal control system, according to the city of Sacramento website.
The center can actively signal timing, but city staff can view traffic through closed-circuit television and also change the lights manually if it is required, the city states.
Jennifer Singer, a spokeswoman for the city, said Sacramento currently operates over 807 intersections with traffic signals. Approximately 550 of them are connected to the city’s traffic center.
“The (Traffic Operations Center) is designed to allow staff to monitor traffic signal operations, traffic conditions, and various traffic data sources,” Singer wrote in an email to The Bee.
While the center can actively monitor and adjust the signal timing based on various traffic conditions and the time of day, Singer said the traffic signals are not manually controlled.
“Traffic signals are a complex system of many components, but each has a traffic signal controller,” Singer said.
According to the U.S. Department of Transportation, a traffic signal controller is an electronic controller that can perform the following tasks:
▪ Control an intersection
▪ Switch signal indications
▪ Signal right-of-way assignments in intervals
▪ Time pedestrian clearance
▪ Time green lights and arrows
▪ Time lane and turn controls
The city’s traffic signals can also detect when vehicles are present.
While some locations have a wire placed in the road to determine when there is a vehicle, the city’s website states that this can cause pavement issues.
To mitigate this, the city also uses video detection.
“The video detection system works by providing an image to a small computer that can detect a change in the image and determine the presence of a vehicle,” the city’s website states.
However, video detection can also fail when there is fog or dust, and trees or the reflection of the sun can skew the images.
Do the traffic lights in Sacramento run on a set timer?
Singer said there are different types of traffic light operations in Sacramento, including some small intersections downtown and midtown that can run a fixed amount of time with basic timers.
“Outside of downtown, the traffic signal controllers take in information from multiple roadway sensors for pedestrians, bicycles, and vehicles to allow the traffic controller to respond to traffic conditions and assign the appropriate amount of time to a direction,” Singer wrote.
The city tries to design a set maximum amount of time for a green light, which Singer said is a preset that should allow the queue of waiting cars to clear or to accept the arriving cars from the nearby signals.
“The roadway sensors allow the signal to move on to the direction that needs service if the vehicles clear early,” Singer said. “This reduces the time it takes to serve other awaiting road users.”
Some of the city’s traffic signals are coordinated, according to the city’s website.
“It is easy to see such coordination on downtown streets,” the website states. “16th Street is a good example of this coordination.”
But the majority, outside of downtown, are two-way signals and not evenly spaced, so they are less likely to follow coordination, the website states.
Can the traffic light cameras see if you run a red light?
Sacramento’s red light cameras are managed by the Sacramento County Sheriff’s Department, according to the city’s website.
“The red light camera system is connected to the traffic signal system and to sensors buried in the pavement at the crosswalk or stop line,” the website states.
While the camera system monitors traffic signals, it is triggered when a vehicle goes over the sensors after the light has turned red.
Once the image is received and, tickets are issued by the sheriff’s department through mail to either the vehicle owner or the driver depending on state law requirements
In Sacramento, there are currently 11 intersections that have red light cameras in operation:
▪ Mack Road and La Mancha Way
▪ El Camino Avenue and Evergreen Street
▪ Howe Avenue and Fair Oaks Boulevard
▪ Mack Road and Center Parkway
▪ Exposition Boulevard and Ethan Way
▪ Broadway and 21st Street
▪ Folsom Boulevard and Howe Avenue
▪ Arden Way and Challenge Way
▪ Fifth and I streets
▪ 16th and W streets
▪ Alhambra Boulevard and J Street
Can emergency vehicles control traffic lights in Sacramento?
Sacramento’s emergency vehicles can control some of the intersections in the city, according to the city’s website.
“Emergency vehicles carry a device that provides a signal to the traffic signal controller,” the website states.
As the emergency vehicle approaches the intersection with its emergency lights on, the website states that the signal controller will end its current timing phase of the traffic light and provide a green light for the emergency vehicle.
“This helps to reduce emergency vehicle response times and increases intersection safety,” the city said on their website.
What do you want to know about life in Sacramento? Ask our service journalism team your top-of-mind questions in the module below or email servicejournalists@sacbee.com.
