How to make car accelerate/decelerate over time

So I'm attempting to make a realistic feeling car. I've got it running, turns feel alright, just how do I make it break appropriately, speed up appropriately, etc etc. I tried, not much luck, but it does stop for a second, go to 8 speed, then go to 30.

 //inspector variables
 
 var speed:float; //speed of the car, tweek as needed based on your scale
 var turnSpeed:float; //turn speed
 var timecar:float;
 var accel: float;
 function Update()
 {
    timecar += Time.deltaTime;
     //grab the input axes
     var steer=Input.GetAxis("Horizontal");
     var gas=Input.GetAxis("Vertical");
 
     //if they're hittin' the gas...
     if (gas!=0)
     {
      InvokeRepeating("addspeed", 1.0, 1.0);
            //take the throttle level (with keyboard, generally +1 if up, -1 if down)
         //  and multiply by speed and the timestep to get the distance moved this frame
         var moveDist=gas*speed*Time.deltaTime;
 
         //now the turn amount, similar drill, just turnSpeed instead of speed
         //   we multiply in gas as well, which properly reverses the steering when going 
         //   backwards, and scales the turn amount with the speed
         var turnAngle=steer * turnSpeed * Time.deltaTime * gas;
 
         //now apply 'em, starting with the turn
         transform.rotation.eulerAngles.y+=turnAngle;
 
         //and now move forward by moveVect
         transform.Translate(Vector3.forward*moveDist);
     }
  }
  function addspeed (){
  if (speed < 30){
  speed++;
  }
  }
 

I've never tried making a racing game in Unity, so I'm completely new to this. I do however have a good amount of experience I Unity as a whole. Thanks for helping!

Just a side-note, the Car Demo provided by Unity won't work, and I didn't want to use it anyways, I prefer making games from scratch.