This paper presents an \eventB model of a speed control system, a part of the case study provided in the ABZ2020 conference. The case study describes how the system regulates the current speed of a car according to a set of criteria like the driver's desired speed, the position of a possible preceding vehicle but also a given speed limit that the driver must not exceed. For that purpose, this controller reads different information from the available sensors (key state, desired speed) and takes adequate actions by acting on the actuators of the car's speed according to the information read. To formally model this system, we adopt a stepwise refinement approach with the \eventB method. We consider most of the features of the case study. All proof obligations of the invariant properties have been discharged using the \rodin provers. Our model has been validated using \ProB by applying the different provided scenarios. This validation has permitted us to point out and correct some mistakes, ambiguities and oversights contained in the first versions of the case study.