Unity car script problem

I am making a car game in Unity and I have created a JavaScript script that lets me move the car around. The scripts works fine unless the car goes over a bump or hill. It will then fly off into the air, regardless of weight and gravity.

I'm reasonably sure this is because transform.translate includes the rotation so if the car is looking up then it will move up because the z axis is pointing up.

The code for the car is:

var speed = 0.0;

var maxSpeed = 6; var minSpeed = -0.5;

var accelerationSpeed = 0.0;

var turnSpeed = 0.0;

var frontLeftWheel : Transform; var frontRightWheel : Transform; var steeringWheel : Transform; var maxSteerAngle = 30;

function Update () { transform.Translate (0, 0, speed); transform.Rotate (0, Input.GetAxis ("Horizontal") *turnSpeed, 0);

var rotation = Input.GetAxis ("Horizontal") * maxSteerAngle; frontLeftWheel.localEulerAngles = Vector3 (0, rotation, 0); frontRightWheel.localEulerAngles = Vector3 (0, rotation, 0); steeringWheel.localEulerAngles = Vector3 (43.99999, 0, -rotation);

getMoveSpeed(); getTurnSpeed();

}

function getTurnSpeed() { turnSpeed = accelerationSpeed;

if (accelerationSpeed <= 0.1)
{
    turnSpeed = 0.1;
}
if (accelerationSpeed == 0)
{
    turnSpeed = 0;
}
if (accelerationSpeed < 0)
{
    turnSpeed = -1;
}

}

function getMoveSpeed() { speed = accelerationSpeed; if(Input.GetKey("up") & (speed < maxSpeed)) { accelerationSpeed += 0.008; }

if (!Input.GetKey("up") & (speed > 0)) {

 if  (accelerationSpeed > 0 & !Input.GetKey("down"))
 {       
     accelerationSpeed -= 0.004;
     if (accelerationSpeed < 0.004)
     {
         accelerationSpeed = 0;
     }
 }

 if  (accelerationSpeed < 0 & !Input.GetKey("up"))
 {       
     accelerationSpeed += 0.004;
     if (accelerationSpeed > 0.004)
     {
         accelerationSpeed = 0;
     }
 }

if (Input.GetButton("Jump")) { if (accelerationSpeed > 0) { accelerationSpeed -= 0.05; } if (accelerationSpeed < 0) { accelerationSpeed = 0.0; } }

} I know its messy but I'm only year 10

If anyone has any ideas on what my problem could be or a better script could they please post it. Thanks