Traffic Signal Operation

Flash Mode

Each traffic signal is hardwired to prevent conflicts, such as a green indication on all approaches. If for some reason the conflict monitor, which is located at each traffic signal, recognizes a conflict, the signal is automatically placed in all-red or yellow-red flash mode, depending upon which direction you are travelling. The traffic signal could also go into a flash mode if there is a power interruption or fluctuation, which is common during lightning storms. The Region of Durham Works Department traffic control signal inventory now numbers over 470, and some of the technology used follows different protocols. What this means is that when you approach a signal flashing red, the opposing direction of traffic may see either a flashing red indication or a flashing yellow. As a motorist, you must approach a traffic control signal in flash mode with extreme caution and proceed only after right-of-way is given. There is a pre-defined procedure that must be followed before Works Department staff can reinitialize the traffic signal so that normal operation can resume.

If you observe a problem with a traffic signal, you may call the Region of Durham Works Department:


Monday - Friday
8:00 a.m. - 5:00 p.m

After Hours

Evening / Weekends / Holidays

Dark Signal

When there is no electricity, such as during a blackout, traffic control signals will go dark, just like streetlights or the lights in your home. As a motorist, you must treat a dark signal with extreme caution and traverse the intersection as if it were an all-way stop.

Emergency Pre-emption

The municipal fire departments in the Region of Durham have the ability to activate signals in their favour when responding to emergency calls. As the fire truck approaches a traffic signal, the driver can "pre-empt" the traffic signal to provide a green indication and thus decrease the response time to the emergency call. If you approach a traffic signal that appears to be operating in a peculiar manner, for example, the green time is very short, it may be due to emergency pre-emption.

Advance Left-Turn Green Arrows

Where there is a dedicated left-turn lane at a signalized intersection, an advance green arrow may be provided at certain times of the day to permit improved efficiency on the road network and reduce queuing. Depending upon the number of vehicles making the left turn, traffic engineers set limits on how long and when the advance green arrow is given to maximize the intersection’s efficiency. For example, in the balance of traffic management it is often more efficient to hold a small number of left turning vehicles than hold a significant number of through vehicles (travelling straight through the intersection). Advance left-turn arrows are only effective for vehicles that have arrived and are waiting at the start of the green phase. If the motorist arrives later in the cycle, the turn will have to be made when there is an available gap in on-coming traffic, during the clearance interval (amber indication), or at the start of the next advance green arrow phase.

Lagging (Delayed) Left-Turn Green Arrows

In situations where queuing might be a problem, the "advance" left-turn green arrow may follow the solid green indication (the through movement). This differs from typical signal operation, where the advance left-turn green arrow precedes the solid green indication. When the length of a left-turn lane is limited due to the proximity of the upstream signalized intersection, it may be preferable to clear the queue before the through lanes are blocked and spill back into the upstream intersection. This method of control is seldom used and is limited to closely spaced intersections in one-way street configurations.

Right-Turn Green Arrows

The green arrow for right turning traffic is sometimes provided at the same time as the opposing advance left-turn green arrow (e.g., the eastbound right turn arrow is given at the same time as the northbound left turn advance arrow).