Vehicle.php

//...
public function forward()
{
    $this->currentSpeed = 15;
    $this->echoStatus("Go !");
}
public function brake()
{
while ($this->currentSpeed > 0) {
    $this->currentSpeed--;
    $this->echoStatus("Brake !!!");
}

$this->echoStatus("I'm stopped");
}

public function echoStatus($status)
{
    echo $status;
}
//...