In FLOW Insights, group operators treat trajectories as groups and filter them based on their aggregated properties like average duration of occurrence.

Level of service

Level of service is a technical term used to describe a quality of vehicle traffic service, with loose definitions of each level. With the LoS operator, you can define your own levels and then filter trajectories based on the level that they currently belong to. FLOW implements the model based on control delay, which in FLOW's terms is the same as duration of occurrence.

Drag the operator to the canvas to see its description and settings.

The operator selects input trajectories based on whether their current LoS falls into a level that has the Pass trajectories checkmark checked. Every road and intersection is different, so find the thresholds that best suit your application. The LoS wiki page provides some example values for at-grade intersections and pedestrian facilities.

With a value widget or sink, you can select the Level of service attribute to export the current level to the dashboard or an external application.

The LoS reported by value widgets and sinks are calculated from average duration of occurrence of input trajectories. With widgets, you can enable history visualisation to see how the LoS on your intersection evolved over time.

It's recommended to use the LoS operator in conjunction with two gates and a movement. Depending on your application, you may want to filter out any motorcycles and bicycles, because they can sometimes pass congested traffic much faster and therefore skew the calculation of the average duration of occurrence and therefore LoS. Here's an example of a basic configuration.

Using the LoS operator alone or with zones is discouraged, because trajectories that have just entered a zone are masked to include only the short part within the zone. Such a part has a very small duration of occurrence (and LoS), but still factors into the calculation of the average, thus skewing it before the traffic object even leaves the zone. When you use gates and movements, the trajectories are only passed and factored into calculations once they finish their movement from the initial to the final gate.

The true power of the LoS operator lies in using it together with I/O interfaces, LoRaWAN, or other APIs. For example, if you add a value widget tied to the LoS attribute, you can use this widget's value to set the output value of an I/O interface. This lets you control traffic devices based on the current LoS. You can e.g. create a rule to send a signal if traffic is bad, warning incoming cars, increasing safety, and alleviating congestion if some participants choose to detour.


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