How do you change a variable in a script, that is on an object instantiated from a prefab?

I'm making a 2d game where the player drives down three lanes at an increasing speed while dodging other cars. When you crash in to another car I want both cars to stop. My problem is that if I just set the cars speed to 0, all the cars stop.

Here is the script on the player:

 var godMode = false;
 var deadCar : Animator;
 static var carCollision = false;
 deadCar = GetComponent(Animator);
 
 
 function OnTriggerEnter2D(other: Collider2D) {
     if (!godMode) {
         //The cars collide
         forwardmover.speed = 0;
         deadCar.SetTrigger("Dead");
         carCollision = true;
     };
 }

Here is the script on the other cars:

 static var carSpeed : float = 5;
 
 function Update () {
     transform.Translate(transform.up * carSpeed * Time.deltaTime);
 }

As I said I want to change the "carSpeed" variable to 0 on the car, I collide with. Any help is very much apreciated