  "Model-free" control and the related "intelligent" proportional-integral (PI)
controllers are successfully applied to freeway ramp metering control.
Implementing moreover the corresponding control strategy is straightforward.
Numerical simulations on the other hand need the identification of quite
complex quantities like the free flow sp\^eed and the critical density. This is
achieved thanks to new estimation techniques where the differentiation of noisy
signals plays a key r\^ole. Several excellent computer simulations are provided
and analyzed.
