Using Arduino with Simulink to build control systems (van speed controller)

The project in short, is a control system to control the van speed in a room according to the number of people inside, using an IR sensor maintained on the entrance of the room to detect one person at each crossing, and the system control the van speed on three levels as below:
Level 1 (min): (0-3) person.
Level 2: (4-6) person.
Level 3 (max): (7-9) person.