Flow intensity ($q$) - is a characteristic of pedestrian flow, defined as the product of the flow speed ($V$) and flow density ($D$):
$q=V·D$
As density increases, the movement speed decreases. Therefore, flow intensity is a bounded function with a maximum. For each contingent, the maximum intensity value and the density at which this maximum occurs are unique.
The figure below illustrates an example of the relationship between speed and intensity as functions of density:
Flow intensity can also be expressed in terms of more practically measurable quantities: the number of people $N$ with horizontal projection area $f$, who pass through a cross-section of width $W$ during a time interval $∆t$:
Note that this formula assumes that flow density is measured in units of $m^2/m^2$.
The relationship between intensity and density, along with the maximum allowable flow intensity for a given path type, is used as a factor to limit the speed of people moving through an opening.
Each type of path has its own maximum flow intensity.