Why does my player move differently than i command?

My character, which is the shape of a car, moves forward and backward when i press the corresponding keys, and when I press the left arrow key the player moves forward and to the left, while curving, like in a circle moving (counterclockwise and Forward) starting as if at 3 oclock and pointed upwards. The problem is when I press the right arrow key, the player moves (Backwards in a clockwise position) as if starting at 3 oclock and pointed upwards. Can someone tell me why this is happening?
(This was written in notepad if that makes a difference)

Thanks for your help

Here is the code I used ( Javascript );

//Javascript; #pragma strict

var forwardRate : float = 25; var turnRate : float = 5;

function Update () {

// forward speed of player var forwardMoveAmount = Input.GetAxis("Vertical") * forwardRate;

// how fast player turns var turnForce = Input.GetAxis("Horizontal") * turnRate;

// rotate player transform.Rotate(0, turnForce, 0);

transform.position += transform.forward forwardMoveAmount Time.deltaTime;

}