We've all dealt with the frustration of really long red lights or really short green lights. So how does the system work?

We got in touch with Mark Berg, the Traffic Engineer for the City of Bismarck to try and understand how all the light systems work.

Our initial goal was to try and find out the longest and shortest lights in Bismarck. But it isn't that simple.

Berg explained that in Bismarck, for the most part, the lights run on three different systems: Fixed Time, Coordinated Mode, and Isolated Mode.


In most of downtown Bismarck, lights will run on a fixed time system. The goal of the fixed time system is actually set up to let pedestrians cross and the traffic comes secondary. The fixed light systems may run on a 70 second cycle for example (but they vary by location). It gets broken up by allowing pedestrians to cross on the walk signal, as well as the flashing don't walk signal and then of course the static don't walk signal.


The lights on State Street between Divide and LaSalle run mostly on a coordinated light system. Those use special video detection systems which is detailed more on Bismarck's city website. You'll notice some lights will have a large white camera next to the light. Those cameras do not record any images or video but are used to detect the traffic flow in any given area.

The traffic flow determined by that video detection system determines how long the lights will last. However the system changes what it looks at depending on the time of day. For example, between 6 a.m. and 8:30 a.m. for example, the system really only looks at traffic coming inbound to Bismarck. There is significantly less traffic going out of Bismarck at that time so the outbound traffic is less important in the algorithms set up by the city.

However, during rush hour in the evening, the video detection system will monitor both inbound and outbound traffic. You will have a lot of drivers who live and work in town going home but also many drivers who live out of town so there is heavier outbound traffic than in the morning.

With varying traffic flow at different locations at anytime of day, light cycles could last anywhere between 75 and 120 seconds.


Then there is isolated time mode. Traffic signals located at the intersection of Washington and Century, and 19th and Capitol are examples of lights that use this mode. In isolated mode, the traffic signal is based solely on a 'vehicular detection system.' In other words, these lights have no time cycle at all. The light will change only based on the flow of traffic. However, these lights even with no set time cycle do have maximum times. So even if no cars are coming, a light will not literally stay on green for an hour for example until a car comes from the side street. A max time is set for the lights to change just in case the detection system fails.


Left turn signals also have different timing based on the time of day. In some cases you may notice that a left turn signal will consistently be flashing yellow even through multiple cycles rather than switching between flashing yellow and solid green.

At the intersection of Bismarck Expressway and 3rd street for example, at 3pm when there is less traffic flow, the city sees no need at any point to hold up traffic on Bismarck Expressway when there will be consistent gaps in traffic. So rather than having that left turn signal be solid green, it will just stay flashing yellow until a heavier traffic time to allow a better flow of traffic.

Sometimes on left turns though, even if there is a green arrow, it could appear really short. Even with a long line of cars, only two to three cars may get through. The goal is to service the "main line" as much as possible. In other words, even if there is a line of seven or more cars in the turn lane, there is still heavier traffic flow coming from Bismarck Expressway and so that gets priority.


Most drivers travel the same routes to and from work everyday and have an idea of the timing of the lights. So if something is off, a driver will usually notice this. There's two potential reasons things could be off. There could be an issue with the system. They run off of computers and sometimes problems do arise and things go wrong. If you do notice anything different, the city actually does encourage you to say something. They rely a lot on public input to time out the lights.

But another reason the light cycle could be out of whack is due to an emergency vehicle.

Some traffic signals have a white confirmation light on them. When that light is flashing it tells the emergency vehicle that they do not have command of the intersection. In other words, the light the emergency vehicle wants to get through is red.

But emergency vehicles have a special system in their vehicles that in case of an emergency they can use to send a signal to the traffic light. At that point, the white confirmation light becomes static alerting the emergency vehicle driver that they have command of the intersection. In other words, their light is green and all the other lights are red.

After this system is used, it could take a few light cycles for the traffic signal to actually get back to its regular cycle. More details on the system can be seen at the city website.


If you are a pedestrian, you may notice that there is a push button to alert the traffic signal that you are there. When you push that button, it actually does do something. When you push it two, three, four, or fifty times, it serves no extra purpose. It does not make the system fail or work quicker. Of course if you punch the button or hit it with some kind of extreme force, then you may actually hurt the system.

But along State Street for example, you will actually never see a walk signal, unless someone physically pushes the button. Pushing the button will not change how long it takes for the light to change in your favor necessarily but it does tell the traffic system that you are there and that it needs to accommodate for someone crossing the street once the light does change in your favor.


Right now the way the city gets traffic information from a particular intersection is by sending an actual person out to the intersection to count how many cars pass through in a 24 hour time period. The flaw in this system could be that on any given day, for whatever reason, when someone is out there monitoring it may not reflect the traffic flow on many other days. But the city will use that one 24 hour period to time out the lights for a six month period for example.

The city is hoping to get a federal grant to install new systems that can detect traffic in real time to get a better idea of the traffic flow in a given area for better timing of the light system.


As mentioned above, the city welcomes public input on the traffic system. Sometimes that is the best way to determine the flow of traffic in a given area. If you experience any issues with traffic flow, call 701-355-1505.

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