I need to make a non user controlled car drive strait

I am making a first person Frogger game and I cant find a simple way to just make the cars drive forward because all of the tutorials are for user controlled cars or complicated AI. I am a beginner by the way.

Well in its simplest form…

public float speed=0.5f;

void Update(){
   transform.Translate(transform.forward*speed*Time.deltaTime);
}