Saturation flow is a key measurement of on-street performance. It is an expression of the maximum capacity of a link as predominantly determined by junction characteristics like geometry, layout, turning radii, visibility, as well as vehicle composition.
Saturation flows are normally required for each individual lane that is modelled, although multiple lanes can be combined into a single measurement if they perform identically in terms of flows. Saturation flows are usually required when modelling signalised intersection or roundabout. Measurements are extracted as vehicles discharge across the stop-line in free-flow conditions and thus unaffected by downstream interference such as congestion or exit-blocking. Computation of the saturation flow per hour is dependent on following parameters:
- Free-flow conditions - GoodVision detects free-flow conditions automatically within the desired time interval and use them for the calculation.
- By default in the UK you need at least 10 free-flow readings to calculate Saturation Flow.
- By default, the minimum free-flow duration is 13 seconds. (can be configured in the app)
- If the headway time between vehicles during the free-flow is greater than 4 seconds, the conditions for measurement of Saturation Flow are considered as over. (can be configured in the app)
- As stationary vehicles get a green indication and start moving, the first two vehicles at the front of the queue are not counted.
A practical example showing how GoodVision extracts saturation flows from video footage can be found in the short video below 👇
Saturation flow calculation in the real traffic example
Saturation flow report can be created in the report builder accessible on the Analyze screen in the Video Insights.
Highlighted variables are adjustable before generating the Saturation Flows report
Generated report will then arrive to your mailbox in a few minutes. Individual saturation flow Excel reports are created for each lane/traffic movement. You will therefore be able to save a substantial amount of man labour hours with this new feature.
Example of the Saturation Flows Excel report where user selected 5s as a maximal time gap allowed in the saturated flow