Power outages happen. Storms knock out lines, equipment fails, and sometimes entire sections of a city go dark. For most people, the immediate concern is the lights in their home or the food in their refrigerator. But out on the road, something else is happening at every intersection in the affected area, and not everyone knows how to handle it.
Most modern traffic signals are designed to fail into a specific mode when power is lost or when the controller detects a fault. That mode is typically flashing red on the main street and flashing yellow on the side street, or in some cases flashing red on all approaches.
Flashing red means the same thing as a stop sign. Every driver on every approach is required to come to a complete stop, yield to any vehicle already in the intersection, and then proceed when it is safe to do so. It functions as a four-way stop, and it keeps traffic moving through the intersection even without an active signal cycle running.
Flashing yellow means yield. Drivers on the yellow approach are not required to stop but must slow down and yield to cross traffic before proceeding.
The specific configuration depends on how the intersection was programmed and what the local jurisdiction has determined is the safest default for that location.
In some cases, particularly during a hard power failure or equipment damage, a signal may go completely dark rather than entering flash mode. No lights at all.
A dark signal should be treated as a four-way stop. That is the legally required behavior in most states, including Colorado. The problem is that not all drivers know this, and an uncontrolled intersection with no visual cues creates real safety risk, particularly at high-speed or high-volume locations.
This is one of the reasons rapid response to signal outages matters. The longer an intersection sits dark, the greater the risk of a collision caused by driver confusion.
Many jurisdictions have invested in battery backup systems for critical intersections. These systems allow a signal to continue operating in full or reduced mode for a period of time after grid power is lost, buying time for crews to respond or for utility companies to restore power.
Battery backup units are typically installed inside or alongside the controller cabinet. They are sized to handle a specific load for a specific duration, often several hours at a reduced cycle or flash mode operation. Like any battery system, they require regular testing and maintenance to ensure they will perform when needed.
Not every intersection has backup power. Priority is typically given to high-volume intersections, locations near hospitals or emergency services, and intersections with a history of outage-related incidents.
When an outage affects multiple signals, maintenance contractors work through a priority list. The most critical intersections get addressed first, whether that means restoring power, switching to manual operation, or establishing temporary traffic control with cones and flaggers while repairs are made.
Response time matters significantly here. A well-maintained signal system with a responsive maintenance contractor means outages get resolved faster and intersections get back to normal operation before the situation creates downstream traffic problems across a network.
At Lighthouse Transportation Group, 24/7 emergency response is a core part of every maintenance contract we hold. When signals go dark, our crews are moving, not waiting for business hours.
The rules are straightforward. A flashing red is a stop sign. A dark signal is a four-way stop. Slow down, stop, yield, and proceed when it is safe. Assuming the other driver knows what to do is how intersections go wrong during outages.
Understanding how the system is designed to fail helps drivers make better decisions when the unexpected happens. That knowledge is worth more than most people realize until they need it.
We’re a small team that loves to create great experiences and make meaningful connections between builders and customers. Join our remote ream!
.gif)