Poiseuille

In the linear laminar flow region, Poiseuille's law describes the hydraulic resistance of a pipe, but in the turbulent flow region the pressure–flow relations become nonlinear.

The Hagen–Poiseuille equation describes laminar resistance.

This system depends on adequate cross sectional area of the airspace above the passengers’ heads in the foot tunnels and escalators, where laminar airflow is proportional to the fourth power of the radius, the Hagen–Poiseuille equation.