PHP OOP with Interface - 2

Mudik.php

<?php 

// INTERFACE

ini_set('display_startup_errors', 1);
ini_set('display_errors', 1);
error_reporting(-1);

interface Vehicle{
    public function getCost($d);
}

class Car implements Vehicle{

    private $toll_fee = 2000;
    private $cost_rate_per_km = 5000;

    public function getCost($distance=1){
        $cost = ($this->cost_rate_per_km + $this->toll_fee) * $distance;
        var_dump("cost using Car is ".$cost);
    }
}

class Train implements Vehicle{

    private $cost_rate_per_station = 10000;

    public function getCost($station=1){
        $cost = $this->cost_rate_per_station * $station;
        var_dump("cost using Train is ".$cost);
    }
}

class Airplane implements Vehicle{

    private $initial_cost = 500000;
    private $rate_per_transit = 100000;

    public function getCost($transit=0){
        $cost = $this->initial_cost + $this->rate_per_transit * $transit;
        var_dump("cost using Airplane is ".$cost);
    }
}

class Mudik{

    private $moda = [];

    public function __construct($configs){
        $this->moda = $configs['moda'];
        var_dump("create mudik instance for relation : ".$configs['from']." to ".$configs['to']);
    }

    public function getCost(Vehicle $vehicle){
        $chosen_vehicle = strtolower(get_class($vehicle));
        var_dump($this->moda['using_'.$chosen_vehicle]);
        return $vehicle->getCost($this->moda['using_'.$chosen_vehicle]['distance']);
    }
}

$configs = array(
    "from" => "Jakarta", "to" => "Yogya",
    "moda" => array(
        "using_car" => array("distance" => 500, "measurement" => "km"),
        "using_train" => array("distance" => 10, "measurement" => "station"),
        "using_airplane" => array("distance" => 0, "measurement" => "transit"),
    )
);

$m = new Mudik($configs);

echo '<pre>';

$m->getCost(new Car);

echo "<hr><br>";

$m->getCost(new Train);

echo "<hr><br>";

$m->getCost(new Airplane);

echo '</pre>';

?>